Introduction to Microbiology Science Notes

Important Points :

→ Many microbes are useful to us, such as bacteria which are used for making curds from milk, yeast used to ferment the batter of bread, bacteria used for making other milk products, bacteria and fungi used for making antibiotics. The bacteria are even used for pollution control.

→ Milk products, cheese, cocoa, pickles made from vegetables, wine and other beverages, bread, probiotic substances and cattle feed are produced with the help of microbes.

Applied Microbiology :

→ Study of the enzymes related to some prokaryotes and eukaryotic microbes, proteins, applied genetics, molecular biology, etc. comes under applied microbiology.

→ Applied microbiology is used for manufacturing various food products and medicines, using microorganisms on a large scale and hence it becomes useful for everybody.

Industrial Microbiology :

→ When microbiology is used for commercial, economic, social purpose and environment related processes, then it is called industrial microbiology. By sustained research on various microbes, various products are produced on large scale by the industrial microbiology.

The main features of industrial microbiology :

→ Using fermentation process, different products such as bread, cheese, wine and raw material for chemical reactions is produced.

→ Solid waste management and pollution control can be done with the help of microbes for garbage management and pollution control.

→ When the milk is converted into yoghurt, a small quantity of Lactobacilli culture is introduced into the warm milk. These bacteria bring about change in the constituents of the milk by fermentation and coagulation. This way yoghurt is produced.

Products :

Dairy Products:

• By preparing various milk products, one can preserve milk for a long time.
• Cheese, butter, cream, kefir, yoghurt, etc. are some important milk products.
• While making these products water content and acidity of the milk is changed. Due to this, texture, taste, aroma and flavour are improved.
• For milk products usually Lactobacilli bacteria are used. Sometimes bacteria in the milk are used for further processes.
• Cheese is produced by using fungi.

Basic process for production of milk products:

• Initial pasteurization of milk to eradicate other harmful bacteria.
• Later fermentation using Lactobacilli.
• Lactose sugar present in the milk Converted into Lactic acid.
• Lactic acid coagulates the milk proteins.
• Compounds with taste and flavour are formed, such as Diacetyl having buttery flavour.

Yoghurt production :

Method of industrial production of yoghurt :

→ Condensed milk powder mixed with milk for more proteins Milk is then boiled Cooled a little.
Streptococcus thermophilus and Lactobacillus delbrueckii bacterial strains added to it in 1 : 1 proportion.
Streptococcus Formation of lactic acid.

→ makes the proteins to gel out → Yoghurt becomes dense. Lactobacilli Formation of Acetaldehyde like compounds Give characteristic taste to yoghurt Yoghurt mixed with various fruit juices → Impart different flavours. E.g. Strawberry yoghurt, banana yoghurt Pasteurization Increases shelf life of yoghurt and its probiotic properties.

Butter :

→ Butter is of two types : Sweet cream and cultured. For large scale production of cultured butter, microbes are used.

Cheese production :

Method for cheese production :

• Cheese is produced from cow milk in the entire world. Intially. chemical and microbiological tests of milk done.
• Lactobacillus lactis, Lactobacillus cremoris, and Streptococcus thermophilus + colours added to the milk.
• Milk turns sour → whey (water in yoghurt) is removed to make milk dense.
• Protease enzyme from fungi is used at present to produce vegetarian cheese.
• Previously, rennet enzyme, from alimentary canal of cattle was used.
• Whey is completely separated from yoghurt.
• To summarise, the steps of process of cheese formation: cutting the solid yoghurtinto pieces → washing → rubbing → salting → mixing of essential microbes + pigments + flavours → Cheese is pressed and cut into pieces → stored for ripening.

→ Mozzarella cheese is used for pizza. Cheddar and Swiss, Blue cheese etc. are used for burgers, Sandwich and other western foods use different types of cheese. E.g. Goat, Cheese, Camembert, Cotija, Chèvre, Feta, Emmental, Gouda, Taleggio, Parmigiano, Regginano, Manchego and Monterey, Parmesan are some of the cheese consumed world-wide especially in the Europe and America.

→ A type of cheese depends upon the milk from which it is produced. The acidity of that cheese, the colours and flavours added, the calcium content present in it are all such factors which decide the type of cheese. Some cheeses are very soft like cream cheese, while some are very hard e.g. Parmesan cheese. Thus, according to taste, flavour and the texture, the cheese become different.

→ In Probiotic food, Lactobacilli bacteria are added. This addition increases the nutritional value of the food. The harmful bacteria, Clostridium are destroyed due to probiotics. They also increase the intestinal flora of bacteria that synthesise the vitamins inside the human intestine. The disease resisting power is also increased due to probiotics.

Probiotics :

→ Milk products containing active bacteria such as Lactobacillus acidophilus, Lactobacillus casel, Bifidobacterium bifidum, etc. form probiotics. All the above microbes help in maintaining the intestinal bacteria which help the digestion. They also decrease the harmful bacteria such as Clostridium.

→ Probiotic products : Various products are called probiotic, such as yoghurt, kefir, sauerkraut (pickle of cabbage) and other pickles, dark chocolate, miso soup, oils, corn syrup. artificial sweeteners, sea food microalgae e.g. Spirulina, ‘Chlorella, Blue green algae, etc.

Benefits of probiotics :

• The colonies of useful bacteria are formed in the alimentary canal.
• The harmful microbes can be controlled by reducing their metabolic activities.
• Probiotics improve resistance to fight against diseases.
• Some harmful substances are formed during metabolic activities. Their bad effects are lowered due to probiotics.
• Due to antibiotic treatment, useful bacteria become inactive. Probiotics revitalize them by making them active again.
• Probiotics are used for treatment of diarrhoea.
• In poultry treatment too, probiotics are used.

• The dough is made by mixing together, the baker’s yeast – Saccharomyces cerevisiae, water, salt and other necessary materials.
• The yeast helps in the fermentation and brings about the conversion of sugar into CO2 and ethanol.
• Due to released CO2 the bread becomes spongy.
• Yeast is of two types : Compressed yeast containing carbohydrates, fats, proteins, various vitamins, and minerals. This is used in commercial bakery industry.
• Dry, granular yeast used for domestic use.
• Products produced with yeast become nutritive.
• Vinegar, soya sauce and monosodium glutamate (Ajinomoto) are also produced by microbial fermentation.
• Vinegar Production : Vinegar is 4% acetic acid (CH3COOH).

Uses of vinegar :

• Impart sour taste to food materials.
• Preservation of pickles, sauce, ketchup. chutneys, etc.
• By fermentation of fruit juices, maple syrup. sugar molasses, starch of the roots, etc. with the help of
• yeast Saccharomyces cerevisiae ethanol is obtained.

Preparation of vinegar :

→ Ethanol + Acetobacter and Glucanobacter mixture → microbial degradation → Acetic acid and other by-products → rarefaction of mixture → Separation of Acetic acid → Acetic acid → bleached with potassium ferrocynide → Pasteurization → vey small quantity of SO2 gas is mixed →Vinegar is produced.

Soya sauce :

→ Fungus Aspergillus oryzae is used to ferment the mixture of flour of wheat or rice and soyabean to produce soya sauce. Production of beverages : Coffee, cocoa, wine and cider are the beverages that are produced from Calfea arabica, Theobroma cacao, grapes and apples respectively. For this production various microbes are used.

→ Different enzymes secreted by the glands associated with the digestive system, help in the digestion of the food. The complex food components are broken down to simple absorbable substances due to the enzymatic action.

→ The pepsin and renin secreted by the stomach; amylase, trypsin and lipase secreted by the pancreas and peptidases and other enzymes secreted by the intestinal glands in the small intestine are the enzymes which bring about catalytic activity and help in the digestion.

→ Microbial Enzymes :

• The enzymes obtained by the activity of microbes are used in the industrial processes.
• These microbial enzymes are better than the chemical.catalysts.
• Microbial enzymes work at the low temperature, pH and pressure.
• Energy is saved in the processes using – microbial enzymes.
• There is no need of erosion-proof instruments for the processes.
• Only specific processes are carried out by the enzymes.
• Unnecessary by-products are not formed during the reactions.
• Purification is not needed and hence expenses on purification are reduced.
• Elimination and decomposition of waste material is avoided.
• Enzymes can be reused.
• Microbial enzymes are thus eco-friendly.

→ Some examples of microbial enzymes are:

• oxidoreductases
• transferases
• hydrolases
• lyases
• isomerases
• ligases

→ Industries that use microbial enzymes :

• Detergents: Used in cleaning process to remove dirt at low temperature.
• Obtaining glucose and fructose syrup from corn flour using enzymes of bacilli and Streptomyces.
• Industries for cheese manufacture, plant extracts, textile, leather, paper, etc.

→ Some microbes are used in the production of amino acids. These amino acids are used in making commercial products. L-glutamic acid, citric acid, gluconic acid, lactic acid and itaconic acid are such amino acids which are prepared by action of certain microbes on some plant sources.

→ Xanthan gum :

• Xanthomonas species is used to make Xanthan gum by fermentation of starch and molasses.
• It is useful due to properties like solubility in hot and cold water and its high density.
• It is used in the production of pigments, fertilizers, weedicides, textile pigments, tooth pastes, high quality paper, etc.

→ Substances obtained by microbial processing are as follows:

• Citric, Malic and Lactic acid
• Glutamic acid, Lysine, Tryptophan
• Nycin and natamycin
• Ascorbic acid (Vit. C), B12, B2
• Beta carotene, lycopenes, xanthenes, lutein
• Polysaccharides, glycolipids
• Vanillin, Ethyl butyrate (fruit flavour), · Peppermint flavour, essence of various fruits and flowers
Xylitol, aspartame

→ Their functions are respectively as follows:

• To make the medium acidic
• For binding the proteins
• Microbial restrictor
• Antioxidants, vitamins.
• Edible colours
• Emulsifiers
• Essence
• Artificial sweetener (low calorie)

→ Carbon compounds obtained from some bacteria and fungi which are able to destroy or prevent the growth of harmful microorganisms are called ‘antibiotics’.

→ It is dangerous to take antibiotics at our own will. They should be taken only when a doctor prescribes to take those. One should not purchase any antibiotic from medical stores without a prescription from a docton One should not use antibiotics according to own will to treat common diseases like a throat infection, common cold or influenza.

→ The dosage of the antibiotics as told by doctor, should be completed, and should not be left half way even if one feels well. Even if we find antibiotic very effective, we should not suggest antibiotics to other people. Antibiotics whose expiry date is over, should never be used.

Antibiotics :

→ Antibiotics are medicines obtained from different types of bacteria and fungi by carrying out certain processes. Some human diseases and veterinary diseases have been controlled due to antibiotic treatment.

→ Antibiotics which are used against Gram positive and Gram negative bacteria:

• Penicillin
• Cephalosporins
• Monobactam
• Bacitracin
• Erythromycin
• Gentamycin
• Neomycin
• Streptomycin
• Tetracyclines
• Vancomycin, etc.
• Rifamycin – against tuberculosis.

→ Bio-degradable substances such as animal and plant wastes, dung and urine of the animals, farm wastes, etc. are decomposed in the biogas plant.

→ The best quality manure and fuel is obtained from the biogas plant. The biogas contains methane, carbon dioxide and HS in small proportions.

→ The methanogenic bacteria present in the excreta of the animals bring about the decomposition of the waste matter.

Microbes and Fuels :

→ Methane is obtained from microbes present in the agricultural and industrial waste, by microbial anaerobic decomposition. This reduces the problem of solid waste management.

→ Fermentation of molasses by yeast, Saccharomyces produces ethanol which is a clean, smokeless fuel.

→ The fuel of future is hydrogen gas. It is released when bacteria perform bio-photolysis of water. Bacteria perform the process of photoreduction to release hydrogen.

→ Some industrial chemicals are produced through microbial process. e.g. Some raw materials that are needed for the industrial processes, such as various alcohols, acetone, organic acids, fatty acids, polysaccharides. For plastic and food products some of these materials are used.

→ Bio-fuel : Biofuel is a good and renewable type of energy. They are easily available and in abundance, hence they are called reliable fuels of the future. Biofuel is available in the following three forms :

• Solid : Coal, dung, crop residue
• Liquid : Vegetable oils, alcohol
• Gaseous : Gobar gas and coal gas.

→ Microbial Pollution Control: With the help of suitable microbes, the problem of environmental pollution is tackled. Biogas, plant, compost production, sewage treatment, etc. are the measures in which microbes are used.

→ Land-filling sites:

• The type of degradable waste which is created in the urban areas is dumped in the land fillimg sites which are ‘away from the residential areas.
• The large pits are dug and then lined with plastic sheets. Used for dumping compressed waste.
• It is covered with certain bioreactor substances and specific biochemicals.
• Microbes present therein decompose the biodegradable materials.
• The pit is sealed with soil slurry after it is full
• Compost is formed by decomposition after few days. This is removed and such land filling sites can be reused after removal of compost.

→ Sewage Management:

• In cities, the sewage is sent to processing plant and is treated with microbes.
• Microbes that carry out decomposition, are mixed with sewage. Such microbes are able to destroy pathogens as well as decompose any compounds.
• Upon decomposition of the carbon compounds present in sewage, microbes release methane and Co,
• The phenol oxidizing bacteria decompose Xenobiotic chemicals present in sewage.
• The sludge formed in this process, is used as fertilizer.
• Environmentally safe water is released after microbial treatment done for the sewage water
Some microbes bring about bioremediation of environment, that are used for treating sewage pollution.

→ Clean Technology :

→ Microbes are used to combat increasing soil, land ard water pollution. Pollutior. control can be done by using microbes that digest hydrocarbons.

→ Microbes used in clean technology :

 Microbes performing tasks of cleaning Function Some microbes Remove the sulphur from fuels. Thiobacilli and Sulphobacilli Conversion of heavy metals into compounds before leaching Hydrocarbonoclastic bacteria (HCB): Pseudomonas spp. and Alcanovorax borkumensis To treat oil spills by destroying the pyridines and other chemicals. Conversion of hydrocarbons into CO2 and water. Vibrio, Ideonella sakaiensis Decomposition of PET (Polyethylene Terephthalate Polyester) Actinomycetes, Streptomyces, Nocardia, Actinoplanes (all bacteria) Decomposition of rubber from garbage. Acidophillium spp. and Acidobacillus ferroxidens Control of soil pollution caused by acid rain. Geobacter Conversion of salts of uranium into insoluble salts.

→ There are various causes of oil spills occurring in the marine waters. For example, accidents of oil tankers that transport crude oil, spillage through offshore oil wells, pollutants released through effluents from shore, etc. The oil spills form an oil film on the surface of water. It causes depletion of oxygen in the water. It also contains hazardous hydrocarbons which results in the death of fish.

→ Microbes and Farming :

→ The leguminous plants have root nodules in which the bacteria, Rhizobium resides symbiotically with the plants such as peas, beans, soyabeans, etc. These bacteria supply nitrates and nitrites and amino acids to the plants. They have capacity to convert nitrogen in the soil and air to form such compounds. This is called bacterial nitrogen fixation.

→ In return the plants provide energy in the form of carbohydrates and the place to stay in the root nodules to the bacteria. Some more bacteria and blue green algae such as Anabaena, Nostoc and Azotobacter, are free living in the soil, they too perform similar function of nitrogen fixation Both types of bacteria make the soil fertile and reduce the demand of chemical fertilizers.

→ Microbial Inoculants :

• Microbes-containing inoculants are produced by process of fermentation.
• They are used for spraying on seeds before sowing. Some of them are released into plants.

→ Benefits of microbial inoculants :

• The nutrients are supplied through the microbial inoculants which help in growth of plants.
The nutritional quality of crops is increased.
• Soil pollution caused by chemical fertilizers is prevented by injecting solution containing Azotobacter and artificial nitrogenase. Such methods are adopted in organic farming.
• Chemicals like fluoroacetamide are mixed with soil as chemical pesticides in agriculture. Such harmful substances can be eradicated by using microbes.

→ Bioinsecticides :

• Through biotechnology, bacterial and fungal toxins are directly integrated into plants to protect them from fungal and pest attacks.
• Insects avoid such plants as they are secondarily toxic.
• Some species of fungi and viruses are also used as pesticides. Spinosad, produced through fermentation is used as a blopesticide.
• Biodegradable plastic, polylactic acid is used for garbage bags. This material is eco-friendly.

Animal Classification Science Notes

Important Points :

• The living organisms are classified according to their basic characteristics, such as presence or absence of nucleus, unicellular body or multicellular body, presence or absence of cell wall and the mode of nutrition in them.

→ The plants are classified according to the following basis :

• Presence or absence of the organs.
• Presence or absence of separate conducting tissues for the conduction of food and water.
• Presence or absence of seeds in plants.
• Whether seeds are enclosed in fruits or not.
• Number of cotyledons in seeds : one or two.

Classification :

• There is great diversity among the animals on the earth. There are about 7 million species of
different animals.
• Depending upon the similarities and differences among these animals, they have been classified. Such systematic classification makes it easy to study the great diverse animal forms.

History of animal classification :

→ To summarize the history of classification :

 Scientist/Taxonomist Basis for classification Method Greek philosopher Aristotle Theophrastus, Pliny, John Ray, Linnaeus Body size, habits and habitats ‘Artificial method’ Dobzhansky and Meyer Body organization, types of cells, chromosomes, bio-chemical properties Natural system of classification Oarl Woese Presence or absence of notochord Method based on evolution Traditional method

→ Benefits of animal classification

• By placing the animals in proper classified groups, their study becomes convenient.
• By studying few animals from each group understanding the entire group becomes easy.
• Animal classification leads to better understanding of animal evolution.
• Identification of animals can be done with great accuracy.
• The relationship of animals with other living organisms is better understood.
• The habitat of each animal and it’s exact role in the nature can be understood by learning animal classification.
• Various adaptations of animals can be studied.

→ Traditional method of animal classification :

Animal classification : Formation of groups and sub-groups of animals by taking into account their similarities and differences is called animal classification.

→ The gross difference between non-chordates and chordates :

 Point of difference Non-chordates Chordates Notochord Absent Present Pharyngeal Gill slits Absent Present Nerve cord Ventral, solid and paired Dorsal, hollow and single Heart Dorsally located Ventrally located

→ Classification of Non-chordates into ten phyla :

• Protozoa (Protista)
• Porifera
• Coelentarata/Cnidaria
• Platyhelminthes
• Aschelminthes
• Annelida
• Arthropoda
• Mollusca
• Echinodermata
• Hemichordata

→ Chordates: All chordate animals belong to the single group which is called Chordata. Chordata has three subphyla, viz.

• Urochordata
• Cephalochordata
• Vertebrata
• Sub-phylum Vertebrata is further divided into following six classes as –
• Cyclostomata
• Pisces
• Amphibia
• Reptilia
• Aves
• Mammalia

→ Robert Whittaker has given five kingdom classification system. All the multicellular, heterotrophic organisms are included under kingdom Animalia or Animal kingdom.

→ According to this system the criteria for classification are as follows:

• Body organization
• Body symmetry
• Body cavity
• Germinal layers
• Segmentation

New (method) system of animal classification :

Criteria for new system of classification:

→ Grades of organization: Unicellular organisms have a single cell. But in multicellular animals ther are many cells.

 Grades of organization Information Examples Protoplasmic grade organization Body made up of only protoplasm. Unicellular animals. Cellular grade organization Many cells are present. But tissues are not formed. Porifera. ‘Cell-tissue grade’ organization Cells performing similar function form the tissues. Tissues perform all body functions. Cnidaria. ‘Tissue-Organ grade’ organization Tissues are organized to form some organs. But complete organ systems are not formed. Flat worms. ‘Organ-system grade’ organization Different organs form organ system to perform specific functions in the body. Human beings and all other higher animals.

Body symmetry:

 Body symmetry Information Examples Asymmetrical No imaginary axis can divide the body into two equal halves. Amoeba, Paramoecium, some sponges. Radial Symmetry An imaginary cut passing through central axis in any plane of body, gives two equal halves. Thus, five different planes passing through central axis of body can divide the body into two equal halves. Star fish and other echinoderms. Bilateral symmetry Only one imaginary axis passing through the body divides it into two equal halves. Insects, fishes, frog, birds, human.

Germinal layers :

 Condition of Germinal layers Information Examples Diploblastic Two germinal layers, ectoderm and endoderm present. Coelenterata/Cnidaria. Triploblastic Three germinal layers, ectoderm, mesoderm and endoderm present. All other animals.

Body cavity:

 Condition of body cavity Information Examples Eucoelomate Body cavity present. During initial embryonic development period body cavity is formed from either mesoderm or gut. All animal phyla from Annelida to higher phyla. Acoelomate Absence of coelom. Porifera, Cnidaria and Platyhelminthes. Pseudocoelomate Body cavity is present but it is not formed by the mesoderm or gut. Hence it is not true coelom. Aschelminthes.

→ Segmentation : Segmentation is the phenomenon in which the body of animals is divided into segments
which are small, similar units. Body with segments is segmented body. E.g. Phylum Annelida shows segmented bodied animals. For non-chordate phyla, refer to the chart.

Kingdom Animalia :

• Non-chordate animals :
• Classification of Subphylum : Vertebrata

→ Chordates :

Phylum – Chordata Animals having a supporting notochord in their body are called Chordates.

→ Characters of phylum Chordata :

• Presence of notochord in the body either throughout the life or at least in the developmental stage.
• Presence of pharyngeal gill slits. (at least during developmental stage).
• Presence of single, tubular and dorsal spinal cord.
• Presence of ventrally situated heart.
• Depending on the notochord, the Phylum chordata is classified into three subphyla.
• Urochordata, Cephalochordata and Vertebrata/Craniata

→ Subphylum – Urochordata

• Urochordates are animals having notochord only in tail region of larvae.
• Larvae are free swimming, they metamorphose into sedentary adults.
• Body is covered by test or tunic. This is a covering like a skin.
• Hermaphrodite animals.
• Examples: Herdmania, Doliolum, Oikopleura, etc.

→ Subphylum – Cephalochordata

• Notochord is present in entire body length
• Small, fish-like, marine animals.
• Large pharynx having gill-slits.
• Unisexual animals.
• Example : Amphioxus.

→ Subphylum – Vertebrata/Craniata

For classification of Vertebrata refer to the chart.

• Vertebrata has been divided into six classes.
• This information has been given in the chart.

Towards Green Energy Science Notes

Important Points :

• The capacity to do work is called energy.
• Potential energy and kinetic energy are the two types of energy.
• Heat, light, electric energy, solar energy, chemical energy, nuclear energy, mechanical energy, etc. are different forms of energy.

Energy and use of energy :

→ Energy is a very basic and primary need. For various types of work, energy is needed in different forms. E.g. Mechanical energy, chemical energy, sound energy, light energy or heat energy.

→ Energy can be converted from one form to another by transformations. This fact is used by man to satisfy his energy needs.

→ We use electric energy in various appliances such as bulbs and tubelights. Fans, iron, refrigerator, water pumps, cellphone chargers, television sets, tape recorders and computers.

→ Electric energy is produced in the generators. By using the principle of electromagnetic induction, the magnetic field around conducting wires is changed and this creates the potential difference. This results in the formation of electric energy.

Generation of electrical energy :

Production of electricity :

• Michael Faraday invented the principle of electromagnetic induction. This principle is largely used in generation of electricity.
• This principle is as follows: A potential difference is generated across the conductor whenever magnetic field around a conductor changes.
• In two ways the field around a conductor is changed.
• Keeping the conductor stationary and rotating the magnet.
• Keeping the magnet stationary and changing the field around the conductor.
• In both cases there is creation of potential difference across the conductor.
• The electric generators are based on this principle. They generate the electrical power.
• In commercial power generation plants → Large generators Turbine having blades rotates the magnet Flow of liquid or gas is directed on the turbine blades → The kinetic energy in the flow Rotates the magnets in the electric generator Electric energy is produced.
• There are different types of power generating stations depending upon the type of energy source that is used to rotate the turbine.

Thermal energy based electric power station :

→ In thermal energy power plants the steam is used to rotate turbines. Coal is burnt Heat energy given to water Water heated in a boiler → Water converted into steam of very high temperature and pressure → Steam in energy used to rotate turbines Generator connected to turbines Electric energy produced. The steam is reused by converting it into water Water recirculated to the boiler.

→ Such power plants are called thermal power plants because thermal energy is used here to generate electrical energy. The chemical energy in the coal is converted into electrical energy gradually through several steps

→ The atoms and molecules present in the coal are formed due to chemical bonds. The energy is stored in chemical bonds. When the coal is burnt, this energy is released.

→ The chemical energy in coal is transformed into thermal energy When water is heated, it converts into steam. This steam in under high pressure and temperature. This force of steam rotates the turbines. The same steam is again condensed and converted back into water. The excess heat in turbine again makes this water turn into steam. In this way turbine rotates very effectively due to steam.

Schematics of thermal power plant :

• Thermal power plant has two types of towers.
• In the power station, boiler, turbine, generator and the condenser are arranged.
• In the boiler, combustion of coal takes place. Gases produced are released in the atmosphere through very high chimney.
• Turbine is rotated by steam at high temperature and high pressure.
• The temperature and pressure of steam later decreases. This steam is then condensed to water by cooling it, in condensers.
• Condensation of the steam takes place due to transfer of heat energy in the steam to the water.
• The heat absorbed by the water is then released to atmosphere through vapour and heated air through cooling tower.
• Most of the electricity generation is done through thermal power plants in India. But there are certain problems in such electricity production.

Problems caused due to thermal power plants :

• Gases like carbon dioxide, sulphur dioxide and nitrogen oxide, etc. soot particles are released due to such burning of coal causing air pollution. This causes serious health problems.
• Especially the respiratory system is affected.
• The coal reserves are limited and exhaustible, Hence there would be problems about its availability.

Power plant based on Nuclear Energy :

→ The energy released by fission of nuclei of Uranium or Plutonium atoms is used to generate the steam of high temperature and high pressure, which is used to rotate the generator for production of electricity.

→ Energy in the atoms + nuclear energy + converted into thermal energy converted into kinetic energy of steam → converted into kinetic energy of turbine converted into electrical energy.

There are proton and neutron in the nucleus of an atom. During nuclear fission, the nucleus undergoes fission either due to natural radiations or due to bombardment of other neutrons on it. The fission liberates the energy which is known as nuclear energy or atomic energy.

Formation of nuclear energy :

• Upon bombardment by neutrons on atom of Uranium-235, absorption of neutron takes place. It converts Uranium-235 into its isotope Uranium-236.
• Being extremely unstable, Uranium-236 transforms into Barium and Krypton atoms through a process of fission. This releases three neutrons and 200 MeV energy.
• Three more Uranium-235 atoms undergo fission due to three neutrons generated in this process. Thus, more fission releases more energy.
• Thus a chain reaction takes place in which the process of fission of Uranium-235 atoms continues.
• In this way a controlled chain reaction is carried out to release thermal energy, which in turn is used for generating electric energy.
 Advantages of nuclear energy Problems of nuclear energy Fossil fuel like coal is not used in a nuclear power plant. Hence air pollution does not occur. Radioactive and harmful radiations are emitted after fission of nuclei occurs. If sufficient nuclear fuel is available, it becomes a good source of electrical energy. The nuclear waste requires very safe disposal. – Very fatal accidents can happen in power plant which emits very harmful radiations.

Power generation plant based on energy of natural gas :

Very high temperature and pressure generated by combustion of natural gas. This gas is used to run the turbine.

In power generation plant based on energy of natural gas three main sections are present.

• Compressor
• Combustion chamber
• Turbine

→ Into the combustion chamber pressurised air is introduced by a compressor → the natural gas burns due to air → high temperature and pressure → runs the turbine → Turbine drives generator → Electricity is produced.

Advantages of power generation plant, using natural gas :

• More efficiency than coal power plants
• Less polluting as there is no sulphur in natural gas. Less pollution by burning of natural gas.
• Use of energy is unavoidable in our daily life but controlled and careful use is essential.

Electric energy generation and environment :

→ Fossil fuels like coal, natural gas and nuclear fuels like uranium and plutonium are hazardous and are polluting. Thus, electrical energy obtained by burning these is not environment-friendly. Excessive use of these fuels cause environmental degradation.

→ Pollution :

• Incomplete combustion of fuels → Carbon monoxide → Adverse effects on health
• Burning of fossil fuels like coal, and natural gas → Emission of toxic gases and soot particles → Air pollution → Problems in respiratory system, like asthma
• Burning of fuels → Increase in percentage of carbon dioxide in the air → Global warming and climate change
• Burning of fuels like coal, diesel, petrol, etc. → Nitrogen dioxide → acid-rain

Non-renewable nature :

• The formation of fossils fuels such as coal, hydrocarbons, crude oil and natural gases (LPG and CNG) took millions of years.
• But their excessive use is depleting these fuels very rapidly. The coal reserves in the world are thought to last for next 200 years and the natural gas reserves for about 200 – 300 years.
• Problems about nuclear energy are tremendous. It emits toxic materials. Disposal of nuclear waste is a difficult problem. Accident in nuclear power plant can be highly disastrous.

Towards the eco-friendly green energy :

Green energy is that energy in which there is no pollution during the generation.

• Energy from water reservoir.
• Energy from wind.
• Energy from sunlight.
• Energy from biofuels, etc. are eco-friendly alternatives of energy production.

→ The sources of such energy are perpetual and sustainable. These types of energy production are pollution-free and eco-friendly. The entire globe is inclining towards green energy

Hydroelectric Energy:

• Hydroelectric energy is a conventional type of energy
• Flowing water → Kinetic energy + Water reservoir → Potential energy.
• Hydroelectric power plant → Stored water’s potential energy → Fast flowing water → Converted into kinetic energy of water → Such speedy water from dam is brought → to the turbine at the bottom level Kinetic energy of the flowing water → drives the turbine → turbine then drives generator electricity is generated.

 Advantages of hydroelectric power generation Problems with hydroelectric power generation Since there is no combustion, there is no pollution. Some villages or settlements are submerged. Possible to generate electricity as and when required. People are displaced and their rehabilitation is the major problem. Water supply can also be achieved due to dam. Fertile land, agricultural plots forests and biodiversity is lost forever. Rains replenish the stored reservoir of the water. Obstruction of the flowing water lead& to adverse effect on the resident aquatic organisms.

Electricity generation using wind-energy:

• The kinetic energy of wind can be converted to electrical energy with the help of wind turbine.
• Such kinetic energy of wind was used for lifting of water, for driving floor mill, etc. in olden times.
• When the wind strikes the blades of the turbine, the blades rotate.
• The axle of the turbine and electric generator are connected through a gear-box which increases the rotations per unit time.
• The rotating blades drive the turbine which in turn drives the generator and produces electricity

→ Wind turbines can produce electricity from less than 1 kW to about 7 MW (7000 kW). The installation of windmills to produce electricity from wind energy depends upon following factors:

• The wind velocity available at the site of installation,
• Geographical factors.

→ Appropriate for installation of wind turbines are done at a particular place. Seashore is most suitable place for installations as here the wind velocity is more. Wind-energy is a clean energy source but due to wind velocity problems its use is limited.

Electric Energy generation using solar energy :

→ Solar energy can be used to make electric energy in following two ways:

• Solar radiations are trapped directly into solar photovoltaic cells without using any transformer. Electrical energy is produced from solar energy due to direct conversion occurring in photovoltaic cells.
• Initially solar energy is converted into thermal energy and later electricity is generated from thermal energy by driving turbine generator system.

Solar photovoltaic cell:

• Solar photovoltaic effect is the conversion of solar energy directly into electrical energy.
• Such generated energy is DC in nature.
• A special type of material called semiconductor (e.g. silicon) is used in making solar cells.
• If a silicon solar cell’s dimension = 1 cm2
Then current = 30 mA and potential difference = 0.5 V.
• Therefore, a silicon solar cell of dimension = 100 cm will generate about 30 mA/cm2 × 100 cm2 = 3000 mA = 3 A current and 0.5 V.
• The potential difference available from a solar cell is independent of its area.

Connections of solar cells :

→ Solar cells connected in series :

→ Solar cells connected in parallel :

 Solar cells in series Solar cells in parallel When two solar cells are connected in series, the potential difference obtained from both the cells is sum of the potential differences of individual solar cells. When two solar cells are connected in parallel, the. potential difference obtained from this combination is the same as the potential difference obtained from individual cell. The current generated from combination in series is equal to the current from an individual cell. The potential differences cannot be added when the combination is in parallel. When solar cells are connected in series, currents from the individual cells cannot be added. The current generated from two cells in parallel is the summation of the currents from an individual cell.

Solar panel :

• Solar panels are formed by connecting many solar cells in series and in parallel.
• Desired potential difference and the current can be obtained by making solar panels by connecting solar cells in series and in parallel.
• The basic unit in solar electrie plant → Solar cell → Solar panel → By joining in a series → String → Many strings joined in parallels → Solar array
• Calculators running on solar energy need marginal power, whereas power stations need power in MW capacity.
• The DC power is available from the solar cells. Therefore, it can be used in applications like electric LED (Light Emitting Diodes) and other appliances that work on DC power.
• Most of the domestic appliances as well as industrial equipment run on AC power.
• Therefore, DC solar power is converted to AC power with the help of an inverter.
Solar energy is available only in presence of sunlight, therefore it is stored in batteries for later use.

• Many solar panels together generate energy that is needed.
• The DC power generated → converted to AC power with help of a transformer voltage and current levels → energy obtained fed into the electricity distribution network.
• Advantages of solar energy: Generation of energy without any fuel combustion and without any pollution.
• Problem of solar energy : Available only on sunny days and during day-time only.

Solar Thermal power plant :

• Solar radiation can be used to produce thermal energy.
• This solar thermal energy is used for electricity production.

• Solar radiation is absorbed by many reflectors that reflect and concentrate it.
• This solar energy is converted into heat energy which is then used to make steam which drives turbines and generate electricity through generators.

Life Processes in Living Organisms Science Notes

Important Points :

• In any environment, there are biotic and abiotic components.
• There are interactions among these components. All such interactions make an ecosystem.

The different components in the ecosystem are as follows :

• Abiotic components: Air, water, soil, sunlight, temperature, humidity, etc.
• Biotic components : All the types of living organisms, like bacteria, fungi, plants and animals.

→ Primary consumers, secondary consumers, tertiary consumers or apex consumers are the different types of consumers. These types are according to the trophic level to which they belong

→ The birds on the tree depend on the aquatic organisms in the lake for their feeding. Birds stay on the trees which are in the vicinity of the lake, so that it is easier for them to capture fishes, frogs, etc. They must also be using the same lake water for drinking.

→ In every ecosystem, there are always interactions between producers, consumers and decomposers. This sequence of feeding interactions is called food chain. In every food chain there are links between four to five trophic levels constituting the producers, primary consumers, secondary consumers. tertiary consumers, etc. The links of food chain are in linear sequence.

→ But food web is a complex network of many small food chains. In fact, food web is the collection of many small food chains. Thus, when many food chains are interwoven, they form food web.

→ By utilizing the solar energy, the green plants perform photosynthesis. Thus, they are producers of the food chain. This food is consumed by the grasshopper. Thus, it is primary consumer. Frog is secondary consumer as its diet consists of insects like grasshopper.

→ Snake is tertiary consumer as it feeds on frogs, while the hawk is apex consumer as it can kill the snake and feed on it. Last picture in the food chain is of fungi which are acting as decomposers. Few bacteria are shown in the picture, act on all the levels and bring about decomposition.

→ If this food chain has to be converted into a food web, there should be interactions between the different components. Any living organism can be prey to different predators. Moreover, a predator can also be a prey for other. Frog eats different insects. The same frog can be either eaten by snake or by hawk.

Ecosystem – A review :

• Biotic and abiotic factors and their interactions with each other form an ecosystem. Every factor has important role to play for functioning of the ecosystem.
• Plants are producers of the ecosystem.
• Various herbivores like deer, goats, sheep, cattle, horses, camels, etc. feed upon producers.
• Carnivorous predators e.g. lion and tiger control the population of the herbivores.
• The decomposers and scavengers like caterpillars, termites, insects present in the dung carry out decomposition and thus clean the environment.
• Existence of human beings is dependent on the balanced ecosystem.

→ Only by decomposition the elements and molecules trapped in the bodies of organisms can be sent back to nature. These various components help in formation of the bodies of plants and animals. If they are not sent back to nature, the cyclic flow of these elements will halt.

→ Only by the decomposition process, foliage in forest, dead trees, and carcasses are sent back to nature. If such decomposition halts for years, the entire earth will be covered by heaps of unwanted garbage. The entire balance of nature would be lost.

→ ‘Jivo Jivasya Jivanam’ is a Sanskrit saying which means that one living organism makes the living on the other. All the food chains occurring in the nature, function on this principle. Prey and predator interactions are based on the above concept. While discussing, students should give various examples that occur in their surrounding environment.

→ The different trophic levels in food chain are producers (First trophic level), primary consumers (Second trophic level), secondary consumers (Third trophic level), tertiary consumers (Fourth trophic level), etc.

→ Energy pyramid is the diagrammatic representation, that depicts the energy levels at the various trophic levels. There are interactions in the form of energy transfer in all the food chains and food web. The energy pyramid shows how energy travels up a food chain.

→ The bird is a part of both the ecosystems. For shelter, the bird builds nest on the tree. That means it takes advantage of tree ecosystem (terrestrial ecosystem). Moreover, it feeds on the fish from the pond. Being a predator, the bird maintains the fish population of the pond and thus it also becomes the part of the pond ecosystem too.

→ Complete the chart: Fill up the blank boxes and display the completed chart in classroom. (Answers are directly given in bold print.)

→ In South India in various places there is paddy cultivation on a large scale → Frequent attack of the grasshoppers on fields → Predator frogs in large numbers → Snakes to feed on the frogs

→ If the population of frog declines, then there will be rise in the population of grasshoppers. The paddy fields will hence be infested with insect pests.

→ The food chain if altered, results in imbalance in the ecosystem. “Paddy → Grasshoppers → Frog Snake’, this food chain is natural. When by any reason there is decline in the number of frogs, thus secondary consumer will also decline. Due to this decline, snake which is at tertiary consumer level will also decline. The primary consumers i.e.grasshoppers will increase as there is now no check on their population.

→ Due to increase in their population the paddy production will be reduced. Due to reduced number of snakes, rats and other rodents from neighbouring areas would also rise, which are also secondary consumers.

→ If frogs’ population declines, there would be imbalance of entire ecosystem. The number of prey and predator populations will change and thus the food chain will come to an end. Everything that is around a living organism is called environment. Environment includes physical, chemical and other natural factors which surround the living organism.

Relationship between Environment and Ecosystem :

• Environment is the collective term for physical, chemical and biological factors that surround the living organisms.
• Many biotic, abiotic, natural and artificial factors together constitute conditions of the environment.

→ Two main types of environment:

• Natural environment: Air, atmosphere, water, land, living organisms, etc.

→ Two main factors in environment :

• Biotic factors
• Abiotic factors.

→ Continuous interactions occur between all the factors in the environment.

• Artificial environment, directly or indirectly affects the natural environment.
• Ecology : Ecology is the science that deals with the study of interactions between biotic and abiotic factors of the environment
• Ecosystem : Ecosystem is the basic functional unit used to study the ecology.
• Many ecosystems together form an environment.

→ Ecosystems constitute biotic and abiotic factors occupying a definite geographical area and their interactions. In environment there are bio-geochemical cycles. These are of two types, viz. Gaseous cycles e.g. nitrogen cycle, oxygen cycle, etc. and sedimentary cycles e.g. phosphorus cycle.

→ Importance of bio-geochemical cycle :

• Plants require water, CO2, phosphorus, potassium, nitrogen, etc. as nutrients while animals require, carbohydrates, proteins, fats, etc. as nutrients.
• Producers and consumers after their death undergo decomposition and release elements which mix with the soil.
• The cyclic movement of nutrients is possible through bio-geochemical cycle.
• The cyclic movement of elements like carbon, nitrogen, phosphorus, etc. continuously occur on the earth.
• By the bio-geochemical cycles, the environmental balance is always maintained.
• If the environment is in proper condition, then human existence is possible. Therefore, it is our responsibility to preserve nature and maintain environmental balance.
• The planet Earth was given to us on lease from our future generations and not as an ancestral property from our ancestors. Therefore, we must conserve it for ourselves and for future generations.

Environmental Conservation :

→ The natural as well as artificial or manmade factors affect the environment. Among natural factors, the sudden changes in the weather, the different types of natural disasters, etc. affect the normal environment. Due to such changes there are problems in the interrelationships that exist between food chain and food web.

→ Due to various man-made causes, there are extreme destruction of environment. Industrialization, the pollution due to such industries, Urbanization, hunting and poaching of wild animals, construction of dams, roads, bridges, etc. are all man-made changes that cause lot of damage to environment.

→ If number of consumers increase gradually, it will create the scarcity of prey organisms. Then due to lack of prey, the number of consumers will also decline.

→ If there are industries established on the river bank, then there is threat to the aquatic ecosystem. It is most likely that the hazardous effluents can be released into the river water. This can cause water pollution resulting into mortality of aquatic organisms.

→ Moreover, this water will no longer remain potable. Hence the health of resident population may also be affected. The food chains and the food web in the river may be terminated due to such pollution

→ The environment is affected due to some natural factors of environment and some man-made factors such as pollution. Such factors create imbalance in the environment which in turn affect the existence of biota. Earth is suffering from many environmental problems caused due to effect of various natural and artificial factors.

→ Environmental pollution : Pollution brings about environmental degradation. It is largely due to natural or man-made causes. Pollution contaminates and makes the unnecessary and unacceptable changes in the surrounding environment. This causes direct or indirect changes in physical, chemical and biological properties of air, water and soil. These changes are usually harmful for all living beings, including human.

→ Reasons for pollution : Population explosion, fast industrialization, and indiscriminate use of natural resources, deforestation, and unplanned urbanization are factors that pollute environment.

→ Our responsibility : Pollution of air, water, noise, soil, thermal, light pollution, etc. are different types of pollution that cause adverse effects. It ultimately affects existence of all the living organisms on the earth. Thus it is our responsibility to curtail polluting substances and aim at environmental conservation.

→ Air pollution, water pollution and soil or land pollution are main types of pollution. In addition to these, light pollution, plastic pollution, noise pollution and radioactive pollution are also other hazardous types of pollution.

→ The pollution which is caused by natural sources and due to natural processes is called natural pollution. E.g. Earthquake and eruption of lava. The pollution that is caused due to human activities is called artificial or man-made pollution.

→ Radioactive pollution : Radioactive pollution is caused by following two causes:

• Natural radiations : Natural processes such as UV and IR radiations.

→ Major mishaps on the international level: Chernobyl, Windscale, and Three Miles Island mishaps. Due to these accidents thousands of people have been affected for long term.

• Cancerous ulcerations due to X-rays.
• Destruction of body tissues.
• Change in the genes.

→ Need of environmental conservation:

• Discussion of the environmental problems – In 1972 at UNO, Stockholm, (Conference arranged on human and environment.)
• Later establishment of United Nations Environment Program (UNEP).
• In India, discussion of environmental issues took place in IV th planning commission.
• A separate environmental department was established later.
• Ministry of environment and forests started various programmes since 1985 in planning, inducting and increasing awareness about environment and forest.

→ People’s participation :

• Awareness about environment conservation rules and laws should be developed for common people.
• Large scale participation of the people in environment conservation can bring about environmental protection and effective conservation.
• Values like positive attitude towards environment and knowledge and quest for the conservation should be imbibed right from school days. Increasing environmental awareness through schools and colleges is essential.
• Every nation has their own future plans about environmental protection and for this purpose they have formulated the laws.

→ Environmental Conservation. Our social responsibility

• Human – environment interrelationship existed since origin of man.
• Human being has become supreme on the earth due to his intelligence, memory, imaginations, creative ability etc.
• Human has used up natural resources without any thought. The development processes have caused extreme damage to the environment.
• Maintaining the environmental balance is the duty of humans.
• Since we have disturbed the environmental balance, only we should think of protection and conservation of nature.

→ Butterflies carry out pollination. This results into reproduction of the plants. The flora is increased due to such increased pollination. Many weeds in the nature are consumed by the butterflies as their food. Some butterflies also consume harmful insects as their prey.

→ Due to beautiful coloured butterflies the environment becomes pleasant and joyful. Butterflies avoid polluted and barren areas. Thus, they indicate the health of the environments. Thus, the ecosystem is said to be in balance if there is presence of butterflies in its surroundings.

→ Laws enacted about environmental conservation :

 Law Year Inclusion in the law Punishment if the law is not followed Forest Conservation Act 1980 Prohibition on the use of the land which is reserved for forest conservation. Imprisonment for 15 days. Environmental Conservation Act 1986 Control of pollution and action on the persons or institutes that harm environment. Five years imprisonment or fine up to Rs. 1 lakh. National Green Tribunal 2010 Effective implementation of environment related laws. Court case. Wildlife Protection Act 1972 Protection of the wild life. Various punishments. Clause 49 A Complete ban on trading of rare animals. Clause 49 B Complete ban on use of articles prepared from skin or organs of wild animals. Clause 49 C Compulsory disclosure of the stock of artifacts made from rare wild animals.

→ Jadav Molai Payeng from Assam has made barren land into a forest which now stands on 1360 acres of land. Now, this forest is known as ‘Molai Jungle’. It is rightly said that “Many people come together to destroy the forest, but a single person, if determined, can establish a new forest”! We must also have such a vision.

Environmental management : Environmental Conservation and Biodiversity :

→ Environmental pollution affects the living organisms and reduces biodiversity.
Living world had a rich biodiversity. This richness of biodiversity is getting depleted at a very high rate only due to various activities of human beings.

→ Biodiversity: The richness of living organisms in nature due to presence of varieties of organisms, ecosystems and genetic variations is called biodiversity. Biodiversity occurs at following three different levels.

→ Levels of biodiversity :

 Genetic Diversity Species Diversity Ecosystem Diversity Diversity among the organisms of same species. The genetic constitution of each organism may be different. Diversity in the species of organisms that occur in the nature. E.g. Various types of plants, animals and microbes. Many ecosystems are present in a particular region. Diversity of the different ecosystems E.g. Natural and artificial ecosystems.

→ Every ecosystem is different from others. It has its own characteristic animals, plants, microbes and abiotic factors.

→ Sacred Groves :

• Some green forest patches were conserved in the name of god by the locals and tribal people. These are considered sacred and hence the name sacred grove.
• These groves are ‘sanctuaries’ conserved by the society.
• Sacred groves have special protection because they are conserved as god’s abode.
• Such patches of thick forests are mostly present in Western Ghats.
• In India, more than 13000 sacred groves have been reported.

→ How can biodiversity be conserved :

• Protection of the rare species.
• Creating National Parks and Sanctuaries.
• Declaration of ‘Bioreserves’, thus offering protection to resident species.
• Conservation of special species by carrying out projects.
• Conservation activities for all living organisms.
• Strictly following the environmental protection rules.
• Recording and maintaining traditional knowledge.
• There are many state-level, national and international level institutes that work for conservation of the environment.

Hotspots of Biodiversity :

• Highly sensitive biodiversity spots in world : 34
• Areas of the Earth were occupied by these hotspots : 15.7%
• Currently, sensitive areas that are destroyed : 86%
• Presently left over sensitive spots on the earth: 2.3%
• Hotspots have 1,50,000 plant species which are 50% of the world count.
• In Eastern India jungles, 85 species are found out of 135 species of animals.
• In Western Ghats about 1,500 endemic plant species.
• Out of the total plant species in the entire world, 50,000 are endemic.

→ Three Endangered Heritage Places of the Country:

 Which one? Where? Problem? . Impact The Western Ghats Gujarat, Maharashtra, Goa, Tamil Nadu and Kerala Endangered animals due to mining industry and search for natural gas. Habitats of Asiatic lion and wild bison under threat. Manas sanctuary Assam Dams and indiscriminate use of water. Tiger and rhino under threat. Sunderbans sanctuary West Bengal Dams, deforestation, excessive fishing, trenches dug. The tiger population and overall local environment is seriously challenged.
• Animals : Asiatic cheetah (Acinonyx jubatus venaticus)
• Namdapha flying squirrel (Biswamoyopterus biswasi)
• Himalayan wolf (Canis himalayensis)
• Elvira rat (Cremnomys elvira)
• Andaman shrew (Crocidura andamanensis)
• Jenkins’ shrew (Crocidura jenkinsi)
• Nicobar shrew (Crocidura nicobarica)
• 22nd May is observed as a World Biodiversity Day.
• International Union for Conservation of Nature (IUCN) prepares the ‘Red List’.
• Red list contains the names of endangered species from different countries.
• The names of endangered species are on pink pages.
• The names of previously endangered but presently safe species are on green pages.

→ Classification of Threatened Species :

 Type of Species Endangered Species Rare Species Vulnerable Species Indeterminate Species Information Number of organisms is declined. Shrunken habitat which can lead to extinction. Considerably declined number of these organisms. Endemic organisms may become extinct very fast. Extremely less number of organisms which further declines. Continuous declining number of organisms is a threat. Organisms appear to be endangered. The data is not enough as they have typical behavioural habits (like shyness) Examples Lion tailed monkey, Lesser florican. Red panda, Musk deer Tiger, Lion. Giant squirrel, Our state animal: ‘Shekhru’

→ If as per report of WWF, 30% of the animal species faced extinction during last 30 years, then it is very alarming. Once lost the flora and fauna will never get replenished. If in future, this rate of extinction continues, there will not be a single animal left on the earth. Only human species will outnumber all others due to no concern for the nature.

→ Some important slogans to spread environmental wisdom:

• Destroying a plant is to destroy everything.
• Practise afforestation to conserve environment.
• Forest is Wealth.
• Environmental protection is value education.
• Provident use of paper is prevention of deforestation.
• To practise the environmental protection is to develop human society.
• Pure air, pure water is key to healthy life.

Life Processes in Living Organisms Science Notes

Important Points (part – I) :

• The food stuffs are digested and converted into soluble nutrients. These nutrients are carried by blood to every cell of the body.
• The oxygen inhaled at the time of respiration is also carried to every cell. In the body cells, this oxygen carries out oxidation of nutrients and thus energy is produced.
• The energy helps the body to carry out all its functions. The nutrients help in the growth and development of the body.

→ Balanced diet has carbohydrates, proteins, fats, vitamins and minerals in the right proportion. Each nutrient carries a specific important function. In balanced diet all these nutrients are in right proportion. Since balanced diet is required for energy and nutrition, it is very important to maintain our health.

→ There are three types of muscles in our body. The voluntary muscles bring about all the movements according to our will. Involuntary. muscles bring about all vital activities of the body. The visceral organs are under the control of involuntary muscles. The cardiac muscles control the movements of heart. Carbohydrates and proteins are stored in muscles.

→ Digestive juice contains different enzymes. Enzymes act as catalysts and bring about the chemical reactions at faster pace. The digestive juices of stomach make pH of digestive tract acidic while that of intestinal juice make it alkaline.

→ Excretory system helps in the removal of nitrogenous waste materials produced in the human body.

→ Due to circulatory system, glucose from digestive system and oxygen from respiratory system is transported to every cell. Red blood cells carry the oxygen as the blood is pumped by the heart. In every cell with the help of oxygen, glucose molecules yield the energy by the process of oxidation.

→ The nervous system and the endocrine system brings about control by nervous and chemical coordination in the body. Due to such coordination different functions of the body are carried out in sequential and controlled manner.

Living organisms and Life processes :

→ There are different systems in the human body. They function in coordination with each other. For this action, they need constant supply of energy.

→ Carbohydrates, fats and lipids in the diet provide energy to the body. The mitochondria present in cytoplasm of the cell synthesise the energy by utilizing these nutrients. For this reaction oxygen is necessary. It is provided by the circulating blood. Each cell is thus supplied with oxygen and nutrients to produce the energy.

→ Plants are autotrophic. They synthesise their own food by photosynthesis. After utilizing some for their own needs, the remaining food is stored in fruits, roots, stem-tubers, leaves, etc. Plant matter is consumed by animals, thus taking the nutrients from them.

→ Carbohydrates :

• Source : Milk, fruits, jaggary, cane sugar, cereals, vegetables, potatoes, sweet potatoes, sweet meats.
• Functions: Carbohydrates provide 4 kcal energy per gram.
• Release of energy from the assimilated food is called respiration.
• Inhalation and exhalation is called breathing.
• When inhalation is done, air enters the lungs.
• The oxygen from this air enters the blood while carbon dioxide from the blood exits from the blood.
• Through exhalation, CO2 is given out. This gaseous exchange occurs through alveolar membrane. This is called external respiration.

→ The RBCs carry oxygen to every cell. Here inside the mitochondria tissue respiration or internal respiration takes place. The oxygen is used for production of energy. By oxidation of food nutrients energy is released in the form of ATP.

Living organism and Energy production :

• Respiration in living organisms takes place at body and cellular level.
• Body level respiration : Exchange of oxygen and carbon dioxide between body and environment.
• Cellular level respiration : Oxidation of foodstuffs inside the cells.
• In one molecule of glucose, there are 6 atoms of Ci.e. Carbon, 12 atoms of Hi.e. hydrogen and 6 atoms of O i.e. Oxygen. Hence glucose is C6H12O6
• These atoms have covalent bonds between them.
• When a molecule is oxidized, it gains oxygen atoms, or it loses electrons.
• Dietary carbohydrates are utilized for production of energy in the form of ATP. Oxidation of glucose is carried out step by step in the cells during a process of cellular respiration.
• Cellular respiration is done by following two methods, viz. aerobic respiration (in presence of oxygen) and anaerobic respiration (In absence of oxygen).
• Aerobic respiration : Oxidation of glucose occurs in three steps during the aerobic respiration. These are glycolysis, tricarboxylic acid cycle and electron transfer chain reaction.

Glycolysis :

→ In glycolysis glucose molecule is oxidized step wise into two molecules of each of pyruvic acid, ATP, NADH2 and water.

→ This process takes place in cytoplasm. Pyruvic acid formed during glycolysis is converted into a molecule of AcetylCoenzyme-A and two molecules each of NADH2 and CO2

→ Tricarboxylic acid cycle : When Acetyl-Co-A molecules enter the mitochondria, the tricarboxylic acid cyclic chain reactions take place in mitochondria. Acetyl part of AcetylCo-A is completely oxidized releasing molecules of CO,2 H2O, NADH2 FADH2

→ Electron transfer chain reaction: The electron transfer chain reaction takes place only in mitochondria. Molecules of NADH2 and FADH2 formed during all above processes participate in electron transfer chain reaction. From NaDH2 molecule, 3 molecules of ATP and from FADH2 molecule 2 molecules of ATP are produced during these cyclic reactions.

→ Along with ATP, water molecules are also formed during chain reactions. Thus one molecule of glucose gives CO2 and H2O along with energy after complete oxidation in the presence of oxygen.

→ The two coenzymes that help in cellular respiration :

• FADH2 – Flavin Adenine Dinucleotide. These co-enzymes are formed in the cell and they take part in cellular respiration.

→ ATP the energy currency of the cell’:

• ATP or Adenosine triphosphate is energy rich molecule.
• There are three components in ATP : Adenine a nitrogenous compound, Pentose sugar, Ribose (C5H10O5) and three phosphate groups.
• Thus it is a triphosphate molecule formed from adenosine ribonucleoside.
• There is energy stored in the bonds by which phosphate groups are attached to each other.
• As per the need of the cell, energy is obtained from ATP by breaking the phosphate bond.
• ATP molecules are stored in the cells as per need.
• In case of less stores of carbohydrates in body, then lipids and proteins are utilized for producing energy.
• Lipids are converted into fatty acids and proteins are broken down to amino acids in such condition. Both, fatty acids and amino acids are converted into Acetyl-Co-A for obtaining energy.
• Molecule of Acetyl-Co-A undergoes complete oxidation by the process of Krebs cycle in mitochondria for releasing the energy.

→ The cellular process and their researchers :

 Process Synonym Researcher Glycolysis Embden- Meyerhof- Parnas pathway (EMP pathway). Gustav Embden, Otto Meyerhof, and Jacob Parnas Tricarboxylic acid cycle Krebs cycle/TCA cycle Sir Hans Kreb

→ Process of energy production through aerobic respiration of carbohydrates, proteins and fats :

→ Anaerobic respiration in living organisms/cells.

→ Energy Production in Microorganisms through Anaerobic Respiration :

• Some bacteria and lower organisms do not live in presence of oxygen. They perform anaerobic respiration for energy production.
• Anaerobic respiration has two steps : Glycolysis and fermentation. During this glucose is incompletely oxidized releasing less amount of energy.
• Pyruvic acid produced through glycolysis is converted into other organic acids or alcohol (C2H5OH) in process of fermentation which is aided by some enzymes.
• If there is deficiency of oxygen level in the surrounding, some higher plants, animals and aerobic microorganisms also perform anaerobic respiration E.g.
• If the soil is submerged under water during germination, seeds perform anaerobic, respiration.
• Similarly, human muscle cells while performing the exercise may also switch to anaerobic respiration.
• This makes the person feel tired due to less amount of release of energy and due to lactic acid accumulation.
• The aerobic respiration or cellular respiration in presence of oxygen performs complete oxidation of glucose.
• Mitochondria is necessary for complete oxidation of glucose.

Energy from different food components :

• Carbohydrates which are not utilized are stored in liver and muscles in the form of glycogen.
• Proteins are formed by amino acids which are held by peptide bonds. Therefore, it is called a macromolecule.
• When proteins are digested, they are converted back into amino acids Amino acids are absorbed in blood circulation and transported to every cell.
• As per the type of cell, the amino acids are again used for making proteins that are required by the body.
 Which protein? Where is it located? Melanin, keratin Skin Ossein Bones Proteins of cell membrane, different enzymes Cells Insulin, Trypsin Pancreas Different hormones Pituitary Gland Flexible proteins : Actin and Myosin Muscles Haemoglobin, Antibodies Blood                  ‘
• Proteins of animal origin are considered to be ‘first class’ proteins. Each gram of protein provides 1 Kcal of energy.
• If protein intake is more than required, it does not result into storage of amino acids in the body. Instead they are broken down forming ammonia which is then eliminated from the body.
• Sometimes, excess of proteins is converted into glucose by process of gluconeogenesis.
• Plants by themselves can produce the necessary amino acids from minerals and then also different proteins.
• The most abundant protein found in nature is an enzyme RUBISCO which is found in the plant chloroplasts.
• Lipids are obtained from oil, butter, ghee, margarine, tallow and oil seeds.
• Lipids are formed of fatty acids and alcohol (glycerol) which have specific bond between them.
• When lipids are digested they are converted into fatty acids and alcohol. Absorbed fatty acids are transported to all the cells through blood.
• Fatty acids produce different substances in different cells.

Examples :

• Phospholipids – produce plasma membrane
• Progesterone, estrogen, testosterone, aldosterone, etc. are hormones produced from fatty acids.
Covering around the axons of nerve cells.
• Adipose connective tissue in the body stores excess of lipids. Each gram of lipids provides 9 Kcal of energy

→ The inflammation or ulceration in the mouth occurs due to lack of enough vitamins in the diet. Therefore, hot and spicy food causes uncomfortable feeling. Particularly vitamin B complex deficiency is said to be responsible for such ulceration.

→ For a better vision, vitamin A is essential. If there is deficiency of Vitamin A in the diet, then there is difficulty in night vision even in childhood or adolescence.

Vitamins :

• Vitamins are required for proper functioning and maintenance of the body.
• The main types of vitamins are as follows:
• Fat soluble vitamins : A, D, E and K
• Water soluble vitamins: B and C.
• Riboflavin (Vitamin B2) and Nicotinamide (Vitamin B3) are necessary for their production of FADH2 and NADH2 respectively.

Water :

• Water is essential nutrient.
• Human body contains about 65 – 70% water. 70% water is present by weight in every cell. Blood-plasma has 90% of water.
• Loss of water or dehydration can cause problems with the functioning of cells and later that of the body.

→ Fibres : Fibres cannot be digested and hence they become helpful in digestion of other substances and egestion of excreta. In leafy vegetables, fruits and cereals there is good amount of fibre.

Cell division : An essential life process :

→ After injury, the cells and the tissues are not able to perform the regular functions immediately. At the site of injury, the blood capillaries rupture and the area gets inflammed. Many cells are damaged. The pain receptor nerves induce pain.

→ As the wound heals there is scab developed. The cells surrounding the wound start dividing rapidly and the cells lost in the injury are restored back. In this way new cells are formed by cell division to heal the wound.

→ It was thought that plants do not have nervous system, so they do not have sensations either. But recent discoveries have proved that plants also have sensations. The tissues that are lost get restored by cell division.

→ Any living organism grows due to the increase in the number of cells in their body. The cells divide regularly and add new cells which are essential for growth. The cell division is thus necessary for the growth of the body and also for the regeneration and repair of tissues.

→ Due to reproduction, the new individual is formed from the existing one. Reproduction can be asexual or sexual. In asexual reproduction, there is mitosis. This cell division helps in forming new individuals. In sexual reproduction, gametes are formed by reduction division called meiosis.

→ Due to chromosomes, gene and DNA the new individual of a species becomes similar to the existing species. Important property of all living cells is cell division.

→ Significance of cell division :

• A new organism is created from existing one.
• Growth of a multicellular organism.
• Restoration of injured and emaciated body.

→ Types of cell division:

• Mitosis and
• Meiosis

→ Important features of mitosis and meiosis :

 Mitosis Meiosis            .. Occurs in somatic cells and in stem cells. Occurs in germ cells Takes place in two stages : Karyokinesis – division of nucleus Cytokinesis – cytoplasm Takes place in two parts. Meiosis – I and Meiosis – II In Meiosis – I there is crossing over and genetic recombination. Homologous chromosomes are divided into two groups forming two haploid cells. Karyokinesis takes place in four stages. It is followed by cytokinesis. Meiosis – I and Meiosis – II take place in four stages each, i.e. Prophase – I Metaphase – I Anaphase – I, and Telophase – I followed by Prophase – II Metaphase – II Anaphase – II, and Telophase – II. Chromosome number does not change. Chromosome number is reduced to half. Mother cell gives rise to 2 daughter cells. Mother cell gives rise to 4 daughter cells.

→ The diploid cells are 2n and the haploid are n. All the normal body cells are always 2n while only gametes formed by reduction division are n.

→ In 2n’ condition, each type chromosome is in pairs while in ‘n condition, there is a single chromosome of each type.

→ Chromosomes are seen only at the time of cell division. Chromosomes are rod shaped and has a primary constriction or centromere. The arms of the chromosome seem to be attached at the centromere. Depending upon the position of centromere and the length of the arms of the chromosome, there are four types of chromosomes.

• Metacentric : It is V shaped chromosome with central centromere and equal chromatid arms.
• Submetacentric : It is L Shaped with centromere somewhere near the mid-point in chromosome. It’s one arm is slightly shorter than the other.
• Acrocentric : Thej shaped chromosome with entromere near one end of chromosome.
• Telocentric : The centromere is right at the end of chromosome resulting into only one arm and thus it looks like ‘1’ shaped.

Stages of Mitosis :

→ Karyokinesis : (Nuclear division)

 Prophase Metaphase Anaphase Telophase Condensation of thin thread-like chromosomes. Completion of condensation of chromosomes. Formation of daughter chromosomes which appear like bunch of bananas. They are then pulled away from each other. Chromosomes reach at opposite poles of the cell and their decondensation begins. Chromosomes become short and thick. Formation of sister chromatids begin. Clearly visible along with their sister chromatids. Splitting of Centromeres with separation of sister chromatids of each chromosome. Their separation begins. Movement in opposite direction due to help of spindle fibres. Chromosomes become thread-like thin and start disappearing. Duplication of centrioles and movement of each centriole to opposite poles of the cells. Chromosomes arranged parallel to equatorial plane of the cell. Formation of spindle fibres between centromere of each chromosome and both centrioles. Each set of chromosomes reach at two opposite poles of the cell. Spindle fibres completely disappear. Nuclear membrane and nucleolus start to disappear. Nuclear membrane completely disappears. Separated daughter chromosomes. Two daughter-nuclei formed in a cell. Reappearance of nuclear membrane and nucleolus.

Asexual reproduction in multicellular organisms :

 Name of the method Process In which organism? Fragmentation The body of parent organism breaks up into many fragments. ’Each fragment lives independently. Spirogyra undergoes fragmentation in favourable conditions. If Sycon breaks up accidentally, each fragment of its body develops into new Sycon. Algae – Spirogyra, Sponge – Sycon Regeneration The body is broken into two parts. Each part regenerates remaining part of the body forming two new organisms. Planaria Budding Repeated divisions of regenerative cells of body wall form a bud.= Progressive growth of bud occurs and a small Hydra is formed. Parent hydra supplies nutrition to the budding hydra. After sufficient growth, new hydra separates and then leads an independent life. Hydra Vegetative propagation Reproduction with the help of vegetative parts of the plants such as roots, stems and leaves. Potato – Eyes on tuber Bryophyllum – Buds on leaf margins Sugar cane, grass – Buds on leaf nodes Carrot, Radish – by roots. Spore formation Sporangia over the filamentous body burst to release spores. Germination takes place in moist and warm place forming new colony. Fungi like Mucor

→ Note: Chromosome number does not change from 2n to an as given in the textbook page no. 18. Under normal conditions such change never happens. The chromosome number never doubles. During cell division initially the centromere of the chromosomes does not divide only chromatid arms divide. The division of chromatid arms take place in anaphase. Thus chromosome number an remains 2n. It never becomes 4n during mitosis.

→ Cytokinesis: Cytokinesis is the division of cytoplasm. In animal cells a notch is formed at the equatorial plane of the cell which deepens gradually and thereby two new cells are formed. In plant cells, a cell plate is formed exactly along midline of the cell.

→ Significance of mitosis :

• Essential for the growth of the body
• Necessary for restoration of emaciated body
• For wound healing
• For the formation of blood cells, etc.

→ Meiosis :

• There are two stages of meiosis : Meiosis-I and Meiosis-II.
• By meiosis from one diploid cell, four haploid cells are formed.
• In meiosis crossing over between non-sister chromatids of homologous chromosomes occur. This results in genetic recombination.
• The four daughter cells formed after completion of meiosis are genetically recombined and not exactly alike and also not exactly similar to their parent cells.
• Spores and gametes are formed by meiosis.
• Meiosis helps to restore and maintain the chromosome number.

→ Meiosis – I :

• Homologous chromosomes undergo crossing over and hence there is genetic recombination.
• The homologous chromosomes are divided into two groups and from these two haploid cells are formed
• Prophase-I of meiosis is lengthy phase which is subdivided into five phases, viz. leptotene, zygotene, pachytene, diplotene and diakinesis. During pachytene, crossing over takes place.

→ Meiosis – II :

• Meiosis – II is similar to mitotic division.
• The two haploid cells that are produced in meiosis – II now undergoes further division forming four haploid cells.

Important Points  (part – II) :

→ The important life processes in living organisms are respiration, circulation, nutrition, excretion, sensation and response through nervous system.

→ The oxidation of nutrients that are absorbed in body is done because of oxygen supplied to cells by respiratory and circulatory system. This helps in liberation of energy. Thus respiration, circulation and nutrition are the life processes that are essential for production of energy required by body.

→ The main types of cell division are mitosis and meiosis. In mitosis, the chromosome number remains the same. 2 daughter cells are obtained from one cell. In meiosis, the chromosome number is reduced to half. From one cell, four daughter cells are obtained.

→ Due to chromosomes, the DNA from parental cells enter into daughter cells. The hereditary characters are transmitted to next generation by cell division.

Reproduction : Asexual and Sexual :

→ Life processes such as nutrition, respiration, excretion, control & co-ordination, etc. keep the organisms alive. The reproductive processes are not essential for survival of the individual but they are important in continuation of species to which that organism belongs In picture ‘a’ vegetative propagation is shown. The twig is planted and it is showing rootlets. This indicates that new plant is being produced.

• In picture ‘b’ hen is laying eggs.
• In picture ‘c’ the seed is germinating and has produced radicle and plumule.
• In picture ‘d’ cell division or binary fission similar to mitosis is shown.
• All the pictures, show different types of reproduction.

→ Maintenance of species means a species undertakes successful reproduction and produces individuals of its own kind. This keeps the species existing on the earth.

→ No. The new organism produced from the old one is not genetically exactly similar to the parents. In meiotic cell division there is crossing over in the homologous chromosomes. This produces genetic recombination. Thus the new organism is different from the earlier one. However, if the reproduction is of asexual type, then the young one is exactly similar to the parents.

→ The type of reproduction, whether it is asexual or sexual, the type of crossing over, the extent of genetic recombination, etc. determine the similarity among the parent organisms and their offspring. Based on this genetic recombination the two organisms of a species do not show exact similarity. However, in case of monozygotic twins there is exact similarity. In asexual reproduction too there is similarity.

→ In the process of reproduction, there is division of chromosomes. Due to cell division, the gametes are formed. The union of gametes produce new offspring. In sexual reproduction, all these processes take place due to cell division In asexual reproduction too there is cell division. Growth of new organism also occurs due to cell division 2.

→ Reproduction is formation of new offspring of same species by earlier existing parent organism. Reproduction is important character of living organisms. Evolution of every species occurs due to reproduction.

→ Two main types of reproduction: Asexual reproduction and sexual reproduction.

→ Asexual reproduction : Asexual reproduction is uniparental reproduction in which there is no formation of gametes. New organism is formed without the fusion of the gametes. The offspring produced is exactly similar to the parent organisms. It takes place by mitotic cell division.

• Demerit of asexual reproduction : Absence of genetic recombination
• Merit of asexual reproduction : Rapid process of reproduction

→ Different methods of asexual reproduction :

Asexual reproduction in unicellular organisms:

 Name of the method Process In which organism? Binary fission The parent cell divides into two similar daughter cells. Occurs either by mitosis or amitosis. Performed usually during favourable conditions Axis can be 1. Simple 2. Transverse 3. Longitudinal Simple : Bacteria and Amoeba Transverse : Paramoecia Longitudinal: Euglena and eukaryotic cell-organelle like mitochondria ‘and chloroplasts Multiple fission Formation of pseudopodia stops, movements stop. Becomes round and covered over by protective cyst. In the cyst repeated nuclear divisions take place forming many nuclei. Cytoplasm divides forming many amoebulae. Cyst persists in adverse conditions. It breaks open after favourable conditions return by releasing many amoebulae. Amoeba in unfavourable conditions. Budding Two daughter nuclei by mitotic division formed by parent cell. Appearance of a small bulge on the surface of parent cell. Bulge is bud. One daughter nucleus enters the bud. Bud separates from the parent cell after sufficient growth. Starts living independently. Yeast cells (Unicellular fungus)

Sexual Reproduction :

→ Reproduction with the help of male and female gametes is called sexual reproduction It has two main processes, viz. gamete formation and fertilization.

→ Gamete formation : By meiosis the gametes are formed. The diploid germ cells give rise to haploid gametes.
Fertilization : From union of haploid male and a female gamete a diploid zygote is formed during fertilization.

→ Subsequent mitotic divisions of zygote form embryo which then develops into new individual.

→ Male parent produces male gamete or sperm and the female parent produces female gamete or ovum. The fusion of these forms zygote. Zygote has recombined genes of both the parents. Hence, the offspring shows some similarities and some differences in the parental characters.

→ Genetic variation gives rise to diversity in living organisms. Those genetic variations that are helpful for adapting to the environment are retained. Such individuals continue to exist and do not become extinct.

→ Diploid (2n) gametes if united, they will form 4n, i.e. tetraploid variety. Such zygote will show severe abnormality. The chromosome number will not be maintained.

→ If meiosis does not happen the gametes produced will be diploid. This will create abnormality. 7. Sexual reproduction in plants :

• Structural unit of sexual reproduction in plants is flower
• Calyx, corolla, androecium and gynoecium are the four floral whorls.

Different types of flowers :

• Bisexual : Flowers with both androecium and gynoecium.
• Unisexual : Flowers with either androecium or gynoecium
• Male flower : Flowers with only androecium
• Female flower : Flowers with only gynoecium
• Pedicellate : Flowers with stalk or pedicel.
• Sessile : Flowers without stalk.

→ Parts of the flower :

Accessory whorls :

 Part of the flower Unit Structure Function Calyx Sepals Green coloured Protective. Keeping all the parts safely covered during bud condition. Corolla Petals Variously coloured To attract insects for pollination.

Essential whorls

 Part of the flower Unit Structure Function Androecium Stamens = 1.  Filament → 2.  Anther 3.  Four Locules -a Pollen grains Stamen is the male whorl. Inside the locules pollen grains are formed by meiosis. Anthers disperse the pollen grains out at proper time. To produce pollen grains. These form  male gametes. Gynoecium Carpels = 1. Ovary : containing one or many ovules. 2. Style : Hollow tube joining the ovary and stigma. 3. Stigma : Tip of style. By meiosis, embryo sac is formed in each ovule. It has a haploid egg cell and two haploid polar nuclei. To produce ovules which forms female gametes.

Pollination : Transfer of pollen grains from anther to stigma is called pollination.

Agents of pollination :

• Abiotic agents : Wind, water
• Biotic agents : Insects, birds or other animals.

Types of pollination :

• Self-pollination : Pollination involves only one flower or two flowers borne on same plant.
Cross-pollination : Involves two flowers borne on two plants of same species.
• In artificial pollination for forming new high yielding and resistant varieties of plants, the pollination with the help of brush, is done by scientists.

Fertilization :

• Pollens fall upon sticky stigma and germinate.
• A long pollen tube and two male gametes are formed upon germination.
• The pollen tube carrying male gametes travels through style and reaches the embryo sac.
• In embryo sac, tip of the pollen tube bursts releasing two male gametes.
• Here fertilization occurs by union of one male gamete and egg cell, Second male gamete unites with two polar nuclei.
• This union forms endosperm. Since two nuclei take part in the process, it is called double fertilization.

Germination :

• The development of new plantlet from zygote after fertilization is called germination.
• After fertilization ovule develops into seed and ovary into fruit.
• Seeds from broken fruits fallen upon the ground start germinating if they get favourable conditions.
• Development takes place due to food stored in endosperm of seed.

Sexual reproduction in human being :

→ Pituitary gland secretes FSH and LH, LH is known as ICSH in males, as its function in the male body is different. From the gonads of male and female, hormones are secreted which are essential for male and female reproductive functions respectively.

→ These hormones are testosterone secreted from testis in males and estrogen and progesterone secreted from the ovaries in females. Testosterone is essential for masculinity as well as for sperm production

→ Human male reproductive system : while female hormones are essential for changes in the female body leading to motherhood. Testosterone in male body and estrogen in female body are responsible for maturity onset changes in human body.

→ The full growth of female body is not completed till the age of 18. Till 18 years of age the physical and emotional maturity is not attained. Therefore, she is not suitable for marriage, sexual relationship and pregnancy. Similarly, boy attains complete growth only by the age of 21.

→ Therefore, to keep individuals and their progeny safe and healthy the Government of India enacted the law to fix the minimum age of marriage as 18 in girls and 21 in boys.

→ Sex determination : Sex is determined according to the sex chromosomes, Human males have 44 somatic chromosomes and XY sex chromosomes whereas human females have 44 somatic chromosomes and XX sex chromosomes.

→ Due to particular sex chromosomal complement, the masculine reproductive system or feminine reproductive system is developed.

Human male reproductive system :

 Organ Structure Function Testes (Pair) Located outside the abdominal cavity in the scrotum, Numerous seminiferous tubules. Each has germinal epithelium → the cells divide meiotically or by meiosis to produce sperms. Testes also produce testosterone. Different tubular structures Rete testes → vas eferens → epididymis → vas deferens → ejaculatory duct → urethra Sperms travel from one tubule to next. In this interval they are nourished and made mature for fertilization. Glands Seminal vesicles Prostate gland Cowper’s glands Secretions released in urethra. All secretions + sperms = Semen Urethra Penis Passage of urine as well as sperms Penis transfers the semen during intercourse. Urethra is a common passage for sperms and urine.

Human female reproductive system :

 Organ Structure Function Ovaries (Pair) In lower abdominal cavity. Produce ova, secrete female hormones. Fallopian duct (pair) Three parts; Free end-funnel like with an opening at centre. Middle part for fertilization. The third part opens in uterus. Entire duct have ciliated epithelium. Transport of ovum to uterus. Uterus In the middle of lower abdomen. Development of foetus, Helping in birth process. Vagina The passage of uterus to outside. Passage for intercourse and also for birth. Bartholin’s glands In the vaginal wall. For lubrication and protection of vagina.

Formation of gametes :

• Sperm from father and ovum from mother are haploid gametes formed by meiosis.
• Man can produce sperms from puberty till death.
• But in a woman the function of reproductive system stops at menopause.
• In mature woman a single matured oocyte is released from ovary every month.
• In woman’s body from birth, there are 2 – 4 million immature oocytes in the ovary of female foetus. Till the age of 45 years woman can produce ova.
• Later she attains menopause due to lessened secretion of female hormones. The reproductive functions then completely stop.

Fertilization :

→ Union of sperm and ovum to form a zygote is called fertilization. There is internal fertilization in humans in which semen is deposited in vagina during intercourse. In the semen there are few millions of sperms. They swim from vagina through uterus and reach fallopian ducts. Only one sperm is required for fertilizing a single ovum that female produces.

→ Women with advanced age have strong chance of conceiving abnormal child. The ova that develop around menopausal age are 45-50 years old and hence they can be abnormal due to faulty meiosis. If such ovum is fertilized there are increased chances of getting genetically abnormal child. e.g. Down’s syndrome or Turner’s syndrome.

Development and Birth :

• The fertilization takes place in fallopian duct. The zygote thus formed undergoes rapid and repeated mitotic divisions to develop embryo.
• It travels from fallopian tubes to uterus. In uterus it gets implanted and grows for next 40 weeks or 9 months.
• The nutrition during this period is provided by placenta which is an organ developed in pregnant mother.
• After completion of embryonic development for 9 months the pregnant mother gives birth to a baby.

Sex determination in human beings :

• The gametes develop from germ cells which are diploid (2n).
• Each diploid cell has 22 pairs of autosomes and 1 pair of sex-chromosomes i.e. (44 + XX or 44 + XY).
• Germ cells undergo meiosis forming haploid (n) gametes having chromosomal combination of 22 + X or 22 + Y.
• Sperms produced are of two types viz. (22 + X) or (22 + Y) but ova/oocytes are all (22 + x) types.
• Sperms complete process of meiosis before they leave male reproductive tract. But the oocytes complete meiosis after ovulation, i.e. only if they are fertilized.

→ Type of sperm of father decides the sex of the child. If X bearing sperm fertilises the oocyte, the girl is born and if Y bearing sperm fertilises oocyte, it’s a boy. Mother has all X bearing oocytes, hence she is neutral in sex determination of the child. Thus mother is not responsible for the sex of child.

→ Girls are equal to boys in every aspect, therefore, female foeticide should be stopped. It is a crime to kill the unborn girls.

→ The hormone oxytocin is released from the posterior pituitary of mother once the foetal development is completed. Due to oxytocin, uterus contracts involuntarily and the baby is expelled out. Thus initiation of birth process is possible due to contractions of uterus.

Menstrual Cycle :

• Menstrual cycle is the naturally occurring repetitive changes in mature human female.
• These cyclic events are controlled by four hormones.
• Follicle stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Estrogen
• Progesterone.
• FSH and LH are secreted from pituitary and estrogen and progesterone are secreted from ovary.
One ovarian follicle develops along with the oocyte present in it due to effect of FSH.
• This developing follicle secretes estrogen.
• This follicle produces estrogen under the influence of FSH.
• Under the effect of estrogen, uterine endometrium develops or regenerates.
• The oocyte also undergoes development.
• Then under the influence of LH, ovulation takes place. Ovulation is bursting of uvarian follicle to release an oocyte.
• The remaining tissue of empty ovarian follicle forms a body called the corpus luteum. It is a secondary endocrine source and it starts producing progesterone.
• Under the influence of progesterone, the uterine endometrial glands secrete and make this endometrium ready for implantation of embryo.
• I’ oocyte is fertilized the endometrium forms placenta along with developing foetus.
• But if it is not fertilized, corpus luteum loses its function and becomes a degenerate body called corpus albicans.
• Corpus albicans does not secrete estrogen and progesterone.
• Due to this, endometrium degenerates and starts sloughing off.
• Degenerating endometrium, unfertilized ovum and blood is discarded out through vagina This results into continuous bleeding for five days which is called menstruation.
• This process is repeated every month. It is interrupted only by pregnancy.
• In breast feeding after parturition, menstrual cycle is suspended.
• The menstruating woman is in pains, she is bleeding, weak and susceptible to infections. Therefore, she needs rest and facilities for personal hygiene.

Reproduction and Modern Technology :

Causes of sterility :

 Causes of sterility in females Causes of sterility in males Irregularity in menstrual cycle. Absence of sperms in the semen. Difficulties in oocyte production. Slow movement of sperms. Obstacles in the oviduct. Anomalies in the sperms. Difficulties in uterine implantation.

Advanced medical techniques like IVF, Surrogacy, Sperm bank, etc. help the childless couple to have a baby.

Modern reproductive technologies :

 Method In Vitro Fertilization (IVF) Surrogacy Sperm Bank/ Semen Bank Process done. Fertilization is done in a test-tube -a embryo implanted in uterus of woman. Oocyte collected from the ovary → fertilized in test- tube by husband’s sperms → Fertilized egg implanted in uterus of other surrogate woman who lends her normal uterus. Ejaculated semen is stored in sperm bank. This semen is used to fertilize egg by IVF technique. Reasons behind the method. Less sperm counts in man. Obstacles in oviduct of woman. Problems in implantation of embryo in uterus of a woman. Various problems in sperm production.

Twins :

• Twins are two embryos that develop simultaneously in the same uterus producing two offspring.
• Two main types of twins are:
• Monozygotic twins
• Dizygotic twins.

→ Monozygotic twins : Formed from single embryo these twins are exactly alike and are of same gender. If within 8 days of zygote formation during the embryonic development cells of that embryo are divided into two groups, then monozygotic twins are formed.

→ Siamese twins : Twins with some parts of body joined to each other are called Siamese or conjoined twins. The Siamese twins are formed if the embryonic cells are divided into two groups, 8 days after the zygote formation. Such twins may also have some organs in common.

→ Dizygotic twins : When two oocytes are released from the ovary of woman and both are fertilized by two separate sperms then there is formation of dizygotic twins. These twins are formed due to two embryos that are separately implanted in the uterus. Such twins are genetically different and may be same or different by gender.

Reproductive health :

• Health: The physical, mental and social well being is called health,
• In India, there is lack of awareness about reproductive health. Social customs, traditions, illiteracy, shyness, etc. keep the society under pressure. There is always indifference towards the reproductive health of women.
• Reproductive health can be achieved by keeping genitals clean.
• Syphilis and gonorrhoea are sexually transmitted or bacterial venereal diseases which affect people on a large scale.
• Symptoms of syphilis : Occurrence of chancre (patches) on various parts of body including genitals, rash, fever, inflammation of joints, alopecia, etc.
• Symptoms of gonorrhoea : Painful and burning sensation during urination, oozing of pus through penis and vagina, inflammation of urinary tract. anus, throat, eyes, etc.

Population Explosion :

• Population explosion : Within a short duration if there had been excessive growth of population, then it is called population explosion.
• Population is growing by leaps and bounds in India. The problems due to population explosion are unemployment, decreasing per capita income and increasing loan, stress on natural resources, etc.
• For population control, therefore in India, family planning is a must.

Heredity and Evolution Science Notes

Important Points :

• The chromosomes made up of nucleic acids and proteins, present in the nucleus of the cell are the components that carry hereditary characters in living organisms.
• The process of transfer of physical and mental characters from parents to the progeny is called inheritance or heredity.
• DNA molecule is made up of two helical strands consisting of deoxyribose sugar, phosphoric acid and
• pairs of nitrogenous bases.
• These three together is called a nucleotide.

Heredity and hereditary changes :

→ Heredity : The transfer of biological characters from one generation to the next one with the help of genes is called heredity.

→ History of genetics:

 Year Scientist Study topic Discovery / Contribution 1886 Johann   Gregor Mendel Pioneer of the modern genetics Series of experiments on pea plant to explain inheritance of characters. 1901 Hugo de Vries Mutational theory Reasons behind the sudden changes. 1902 Walter, Sutton Study of chromosomes Paired chromosomes in grasshopper cells. 1944 Oswald Avery, Mclyn McCarthy and Colin MacLeod DNA All living organisms have genetic material in the form of DNA (except viruses). 1961 Francois Jacob and Jack Monod Protein synthesis A model for process of protein synthesis with the help of DNA in bacterial cells.

→ After the process of protein synthesis was discovered …

• Genetic codes hidden in DNA were understood.
• Field of genetic engineering was developed.
• Emergence of the technique of recombinant DNA technology.

→ The benefits of science of heredity :

• Diagnosis of hereditary disorders.
• Treatment of incurable hereditary disorders.
• Prevention of hereditary disorders.
• Production of hybrid varieties of animals and plants.
• Use of microbes in industrial processes.

→ The purines are of two types, viz. adenine and guanine and pyrimidines are of two types viz, cytosine and thymine. The adenine always pairs with thymine with double hydrogen bonds while cytosine always pairs with guanine with triple hydrogen bond. The helices remain bound due to these hydrogen bonds.

→ DNA: DNA molecule is a double helix consisting of two strands. Each strand of this helix is made up of nucleotides. Each nucleotide is made up of a phosphoric acid, a deoxyribose sugar and a nitrogenous base. Nitrogenous bases are of two types, viz. purines and pyrimidines.

→ RNA : RNA is nucleic acid taving single strand of ribonucleotides. Each ribonucleotide is made up of ribose sugar, phosphate molecules and a nitrogenous base. There are four types of nitrogenous bases, viz. adenine, guanine, cytosine and uracil. RNA is found both in nucleus as well as in cytoplasm.

→ According to the functions RNA is of the following three main types: mRNA, RNA and tRNA

→ mRNA carries the information for protein synthesis from genes on DNA chain in nucleus to the ribosomes in the cytoplasm. Therefore, it is called messenger RNA.

→ rRNA is the component of the ribosome. It helps in protein synthesis.

→ tRNA is present in the cytoplasm. According to the message of the mRNA, it carries the specific amino acid up to the ribosomes as per the message coded on mRNA

→ Genetic disorders are caused due to abnormalities in chromosomes and mutations in genes. Some important causes of genetic disorders are as follows:

• Increase or decrease in number of chromosomes causing numerical change.
• Deletion of any part of the chromosome
• Translocation of chromosomes.
• Sudden change or mutation occurring in a normal gene, turning it into a defective gene.
• Mutations in more than one gene at the same time causing polygenic disorder.

→ Examples: Disorders due to numerical changes in the chromosomes :

• Down’s syndrome.
• Turner’s syndrome
• Klinefelter’s syndrome.

→ Monogenic disorders caused due to mutations: Hutchinson’s disease. Tay-Sachs disease, galactosaemia, phenylketonuria, sickle cell anaemia, cystic fibrosis, albinism, haemophilia, night blindness, etc.

→ Polygenic disorders: Cleft lip, cleft palate, constricted stomach, spina bifida (a defect of the spinal cord), etc. are polygenic disorders. Diabetes, blood pressure, heart disorders, asthma, obesity are also polygenic disorders.

Transcription, Translation and Translocation :

Transcription :

• Synthesis of mRNA as per the nucleotide sequence present on the DNA molecule, is called the process of transcription.
• The nucleotide sequence present in the DNA molecule is called gene. Genes control the structure and functioning of cells of the body.
• Information required for the synthesis of proteins is stored in the genes i.e. in the nucleotide sequences of DNA. The proteins are synthesised according to the need of the body.
• ‘Central Dogma’ : Synthesis of proteins by DNA through the RNA is called central dogma.
• DNA Transcription RNA Translation Protein

• Genetic information is thus used from DNA to RNA, then through RNA for protein synthesis.
• mRNA is produced according to the sequence of nucleotides on DNA.
• During transcription only one of the two strands of DNA is used.
• The sequence of nucleotides present on DNA strand gets copied in mRNA. Hence there is always complementary sequence produced on the new mRNA molecule.
• RNA molecules have uracil instead of thymine present in DNA.
• Thus by transcription mRNA molecule which is complementary to DNA is produced.

→ Role of different RNA in protein synthesis :

Triplet codon :

The code for each amino acid consisting of three nucleotides, is called ‘triplet codon’.
mRNA formed in nucleus brings the coded message from DNA when it comes in cytoplasm. This message contains the codes for amino acids.

Dr. Har Govind Khorana, made an important contribution in discovery of triplet codons for 20 amino acids. He was awarded the Nobel Prize in 1968 for this work, along with two other scientists.

Thousands of triplet codons are present in each mRNA molecule. As per the message on mRNA amino acids are supplied by the tRNA.

Translation: As per the codon on mRNA, the tRNA molecule with complementary ‘anticodon’ is brought near mRNA, this process is called translation’.

Formation of peptide bonds: Every tRNA brings specific amino acid. These individual amino acids are joined together by peptide bonds with the help of rRNA.

Translocation: The ribosome keeps on moving from one end of mRNA to other end by the distance of one triplet codon. This process is ‘translocation’.

Many such polypeptide chains come together to form different and complex proteins. The proteins are essential for controlling various functions of body of living organisms.

Mutation :

Sudden change occurring in the genetic material is known as mutation.

Due to transmission of parental genes to offspring, there is remarkable similarity between parents and their offspring. But if there is mutation in any nucleotide then there are changes in the characters of the offspring. Mutations are of two types, viz. minor and major. Minor mutations can also bring about considerable changes. E.g.

Genetic disorders like sickle cell anaemia is caused due to mutation. Mutation is an everlasting process which leads to the process of evolution. It also offers proof for Darwin’s theory of natural selection. Appendix of human digestive system is a functionless or vestigial organ, Wisdom teeth are not useful for chewing the food.

Dinosaur could not adapt to the environment in which they were trying to survive. There was beginning of ice age which resulted in scarcity of food. The starvation was one of the reasons for extinction. According to one theory, a meteor collided with the earth and this resulted in catastrophic death of the dinosaurs.

There is continuous and rapid change in the environment which is causing threat to the natural habitats of the animals and birds. Pollution, climate change, increasing urbanization etc. are the factors causing depletion of food and shelter of animals and birds. Moreover, hunting and poaching has also resulted in extinction of many species.

Evolution :

• Evolution : The gradual change occurring in living organisms over a long duration is called evolution. Evolution results in the development of organisms.
• Transformations ranging from changes in the stars and planets, to the changes in biosphere on the earth are studied in field of evolution.
• Due to evolution, there is formation of new species. Due to natural selection, there are continuous changes in specific characters of several generations of living organisms.
• Approximately 3.5 billion years ago, life was not present on the Earth.

→ The living organisms have been developed according to the following phases:

• Simple elements
• Organic and inorganic compounds
• Complex Organic compounds such as proteins and nucleic acids
• Mixture of different types of organic and inorganic compounds.
• First primitive type of cells
• Processes to take up surrounding chemicals developed leading to growth of cells in numbers →
• First living organism those organisms that could adjust and adapt to the surrounding conditions, survived and grew.
• This is according to the principle of natural selection.
• Some of them that could not adjust, perished.
• Ranging diversity in animals : From unicellular amoeba and paramoecium to giant whale and man.
• Ranging diversity in plants : From unicellular Chlorella to the huge banyan tree.
• Existence of life on Earth: From equator t both the poles on the entire earth, living organisms are seen in air, water, land, rock, etc.
• Theory of “Gradual development of living organisms’ is accepted worldwide.

→ Theory of Evolution :

• First living material is the protoplasm which was formed in the ocean.
• This gave rise to unicellular organisms in gradual time.
• Over the span of approximately 300 crore years, very gradual changes occurred in the unicellular organisms which slowly evolved into larger and more complex life forms.
•  All round and multi-dimensional changes occurred which resulted in evolution of different types of organisms.
• Organizational evolution : The progressive development of plants and animals over a very large period of time is called organizational evolution.
• Evolution : Development of living organisms from the ancestors having different structural and functional organization is called evolution,

Evidences of evolution :

→ Evolution is an everlasting process of changes. The proofs to support this process are called evidences of evolution which are of following types:

→ Morphological Evidences :

• Similarities in the external and visible features are called morphological evidences.
• In animals, similarities in the structures such as mouth, nostrils and ear pinnae, position of eyes, thickly distributed body fur or hair.
• In plants, similar characters such as leaf shape, leaf venation, leaf petiole, etc.
• These similar features indicate that origin of different animal or plant groups must be the same having a common ancestor.

→ Anatomical Evidences :

• Human hand, forelegs of bull, flipper of whale and patagium of bat show difference in their features.
These organs also have different uses.
• However, the structure of bones and joints in organs of each of those animals show similarity.
• This is an indication that all these animals originated from a common ancestor Higher organisms show different body organs and systems that carry out specific functions.
• Each system consists of definite organs.
• In the thoracic cavity, there are lungs and heart. In skull, brain is located. In abdominal cavity there is stomach, intestine, liver, kidney, etc.

Each important vital organ performs specific function which is necessary for survival. Brain controls and coordinates all the vital activities. Heart is responsible for the circulation of blood throughout the body. Lungs perform respiration.

Kidneys filter out nitrogenous waste products from the blood. In this way, each organ performs its own function. Only few organs such as appendix do not perform any function.

→ Vestigial Organs :

• Vestigial organs : The degenerated or underdeveloped organs which cannot perform any function are known as vestigial organs.
• Existing organs undergo gradual changes during evolutionary process. Thus, they form new tissues, organs, etc.
• Under certain environmental conditions such changes are necessary. However, some structures become useless in newly changed conditions.
• Due to natural selection, such structures undergo degeneration and after a very long time span they vanish.
• Appendix may be useful for grazing, ruminating herbivores but it is vestigial for man.
• Other vestigial organs in human body are tail bone (coccyx), muscles of ear pinna, wisdom teeth, and body hairs.

Paleontological Evidences :

→ Fossil: Fossils are remnants of living organisms or their impressions which are preserved deep down in the earth’s surface. Various natural calamities buried organisms in this way. Fossils throw light on the evolutionary process as they offer direct evidence of evolution.

→ Carbon dating : Carbon dating is a technique to understand the age of a fossil. When alive, animals and plants consume carbon continuously but this process ends after their death. Later their body carbon in the form of C-14 undergoes continuous decaying process. C-12 is not radioactive. Therefore, the ratio between C-14 and C-12 changes continuously.

→ By calculating the following three aspects, the age of the fossil can be determined by knowing I. The time passed since the death of a plant or animal II. Measurement of the radioactivity of C-14. III. The ratio of C-14 to C-12 present in the body.

→ Uses of carbon dating :

• Study of palaeontology
• Understanding anthropology
• Determining the age of human fossils and manuscripts.
• Calculating the age of fossils and placing them in geological time scale
• Deducing the information about other former organisms. E.g. Invertebrates gave rise to vertebrates gradually during evolution.

→ Willard Libby : Willard Libby developed the technique of carbon dating method which is based upon the radioactive decay of naturally occurring C-14. For this contribution he was awarded the Nobel Prize in 1960. In the journal ‘Radio Carbon’ the data about the ages of the materials determined is compiled and published.

• Connecting Links : Some organisms share morphological characters of two groups and hence they are called ‘connecting links’.
• Peripatus : It shows characters of Annelida and Arthropoda and thus it is the connecting link between these two phyla.
• Annelid characters : Segmented body, thin cuticle, and parapodia-like organs.
• Arthropod characters : Tracheal respiration and open circulatory system.
• Duck billed platypus : Duck billed platypus is the connecting link between Reptiles and Mammals.
• Reptilian characters : Egg laying habit, scales on body.
• Mammalian characters : Presence of mammary glands and hair.
• Lung fish : Lung fish is the connecting link between fishes and amphibians.
• Fish characters : Fish like body.
• Amphibian characters : Respiration with lungs. The above connecting links prove that arthropods evolved from annelids, amphibians evolved from fish and mammals evolved from reptiles.
• Embryological Evidences : All vertebrate embryos show extreme similarities during initial stages of development. These similarities disappear gradually in later development.
• This initial similarity indicates that there may be a common origin of all these animals.

Darwin’s theory of natural selection :

• Charles Darwin : (1809-1882) proposed the theory of natural selection. This theory is an important milestone in the study of evolution.
• Theory of natural selection : “The survival of fittest’, i.e. organisms which are fit for survival, evolve while those that are not perish. The natural selection thus acts to produce new species.
• Theory of natural selection is given in the book, Origin of Species’ which is written by Darwin,
• For this study of evolution, Darwin had collected and observed innumerable specimens of plants and animals.

→ Important explanation of Theory of natural selection :

• All living organisms reproduce prolifically,
• There is competition with each other or struggle for survival.
• Organisms that show essential modifications for survival, sustain while remaining perish.
• Survival of the fittest and elimination of misfit is the natural selection’.
• Well adapted, sustaining organisms reproduce more such offspring and in turn produce new species having specific characters.

→ Objections to Darwin’s theory :

• Some more factors are responsible for evolution and not just the natural selection.
• Any explanation about useful and useless modifications was not provided by Darwin.
• Causes of slow and abrupt changes was not explained by Darwin.

Lamarckism :

• Jean-Baptiste Lamarck (1744-1829): Lamarck proposed principle of ‘use or disuse of organs and ‘theory of inheritance/ancestry of acquired characters’.
• His concepts are known as Lamarckism.
• Every living organism tries to evolve. During its lifetime, it acquires certain characters through adaptations and modification.
• These characters are passed to the next generation.
• Depending upon the activities or inactivity of that organism these changes occur.

→ Examples of acquired characters :

• For several generations, giraffe extended the neck for browsing on leaves from heights. Due to such extension of neck , giraffe became long-necked.
• Due to frequent hammering movements, shoulders of the ironsmith became very strong.
• Flightless birds like emu and ostrich have weak wings as they do not fly.
• Due to wading and swimming in water the hind limbs of aquatic birds such as swan and duck became fitter for such mode.
• Due to burrowing habit, snakes lost the limbs. According to Lamarck such acquired characters are inherited by the next generation.

→ Objections to Lamarckism :

• The view that unused organs degenerate and used ones evolve was accepted but inheritance of such characters was not agreed by the scientists.
• Modifications formed are not transferred to the next generation.
• Ancestry/Inheritance of acquired characters : This concept states that the living organism is able to transfer the characters which it has acquired, to the next generation.

Speciation :

• Due to evolution, new species of plants and animals are formed.
• Species : The group of organisms that can produce fertile individuals through natural reproduction is called species.
• Speciation: The process of formation of new species from earlier ones is called speciation.
• Each species possesses specific characters. Each species differs in its geographical conditions, food preference, habitat, reproductive ability and period, etc. Therefore, the specific characters are retained

→ Speciation depends upon following factors :

• Genetic variation
• Geographical changes
• Reproductive changes
• Geographical or reproductive isolation for a long period.

Human Evolution :

→ Stages of human evolution :

→ Around 2 Crore years agd some species of apes started evolving in different direction.

• Changing climate, dry environment, loss of forest cover,
• Apes descended from trees and started living on land. (Arboreal → terrestrial transition)
• Increasing use of hands for feeding and working.
 Approximately Africa and some Walking on two legs, instead of four. First human-like animal: 2 crores years ago. parts of India Development of lumbar bones. Walking semierect Ramapithecus

 When? Where ? What happened? Who were extinct? Who evolved? Approximately 40 lakh years ago. South Africa Ape became larger and more intelligent. Approximately 15 lakh years ago. China and Indonesia in Asia Skillful man. Man who could walk upright. Human like animals evolved. Rise of genus ‘Homo’. Approximately 1 lakh years ago. Africa, Asia and Europe Upright walking human. Enlargement of brain First member of Wise man (Homo sapiens neanderthalensis) Neanderthal man was very intelligent Well-developed brain. Use of fire. Approximately 50,000 years ago. Africa, Asia and Europe Evolution at very fast rate. Cro-Magnon man 10,000 years ago On entire earth Invention of agriculture.Rearing of cattle. Establishing cities and civilizations. Development of culture. Homo sapiens sapiens (Wise man)                   ’ 5000 years ago On entire earth Invention of art of writing and beginning of historical periods. Modern man 400 years ago On entire earth Emergence of Modern sciences Cultural evolution of man 200 years ago On entire earth Rise of industrial society
• Important: First record of human-like animal: ‘Ramapithecus
• First example of wise-man: Neanderthal man

→ Stages of human evolution and its time :

 Stage of human evolution Time period 1. Ancient animals like Lemur 7,00,00000 years ago 2. Egyptopithecus 4,00,00000 years ago 3. Dryopithecus 2,50,00000 years ago 4. Ramapithecus 1,00,00000 years ago 5. Australopithecus 40,00000 years ago 6. Skilled Human 20,00000 years ago 7. Man with erect posture 15,00000 years ago 8. Neanderthal 1,50000 years ago 9. Cro-Magnon man 50000 years ago

Space Missions Science Notes

• The visible portion of the atmosphere and outer space seen by simple eyes, without any equipment from the earth, is known as the sky.
• The infinite three-dimensional expanse in which the Solar system, stars, celestial bodies, galaxies and the endless Universe exist is known as space.
• Both sky and space lack a definite boundary However, the sky is a very tiny part of space.
• Our Solar system is a very tiny part of a huge Galaxy-Milky Way.
• The Sun is at the centre of the Solar system. Sun is a star.
• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune are planets in our Solar system.
• These planets revolve around the Sun. Some of these planets have their own natural satellites.
• Besides, there are asteroids, meteoroids, comets and meteors in the Solar system.
• An astronomical object orbiting any planet of our Solar system is called a satellite.
• Mercury and Venus have no satellites.
• Some planets have more than one satellite. E.g. Jupiter has 69 satellites.
• The earth has one natural satellite called the moon.

→ The following three types telescopes are orbiting around the earth :

• Optical Refracting Telescope.
• Optical Reflecting Telescope.

→ Visible light and radio waves emitted by celestial bodies in space pass through the atmosphere before reaching the earth’s surface. During this journey, some light is absorbed by the atmosphere. Hence, the intensity of the light reaching the earth’s surface decreases. Besides, temperature and air pressure cause the atmospheric turbulence.

→ Hence, light rays change their path, resulting in a change in the position of the image of a celestial body. City lights during night, and bright sunlight during day also put limitations on usage of optical telescopes on the earth. To minimize these problems, optical telescopes are situated on mountain top, away from inhabited places. However, limitations caused by the atmosphere still persist.

→ To get rid of these problems scientists have successfully launched telescopes in space. Images obtained by these telescopes are brighter and clearer than those obtained by the telescopes located on the earth’s surface.

→ The first person to go into space in a spacecraft was Yuri Gagarin of the then USSR. He orbited the earth in 1961. The first person to step on the Moon (1969) was Neil Armstrong of USA. Rakesh Sharma of India orbited the earth in 1984 in a Russian spacecraft.

→ Kalpana Chawla and Sunita Williams of Indian origin also participated in space explorations through missions organized by NASA (National Aeronautics and Space Administration) of USA.

→ In nearby area of our residence, many mobile towers are installed at various places. Cellphones receive signals from one of these mobile towers.

→ All mobile towers are connected to satellites. Cellphone signal reaching the nearest mobile tower in our vicinity is first transmitted to the satellite. The satellite transmits the signal to the mobile tower near the destination.

→ Television Centre or Studio transmits the TV programme which first reaches the satellite. The dish antenna of the cable operator in our area receives these signals. The TV programmes reach our TV set through a cable connected between the cable operator’s receiving station and our TV set.

→ Alternatively, a small portable dish antenna fixed on the rooftop is also used to receive the TV signals directly from the satellites. Finally, a cable connected to the dish antenna and TV set brings the programme to our TV set.

→ Weather satellites take photographs of the sky above the earth’s surface at regular intervals. Some satellites, capable of receiving radio signals, also collect the information of weather conditions and finally images of the sky are built with computers. Territorial boundaries of the states and the country are drawn later on these images. Such satellite images with imposed boundaries are printed in media or shown on the television.

→ Students can prepare this presentation on the basis of the following outline:

• Formation and objectives of ISRO
• Indian space scientists
• Space missions of India
• Current functional satellites of India
• Research and other centres of ISRO in India
• India’s moon mission and mars mission
• Information regarding the launching of satellites of other countries by India.
• Indian astronauts and astronauts of Indian origin
• Future plans of India’s space mission.

→ Keep it in mind/Do Remember :

• INSAT : Indian National Satellite
• GSAT : Geosynchronous Satellite
• IRNSS : Indian Regional Navigation Satellite
• System IRS : Indian Remote Sensing Satellite
• GSLV : Geosynchronous Satellite Launch
• Vehicle PSLV : Polar Satellite Launch Vehicle

Carbon Compounds Science Notes

Importent points :

• Organic and inorganic compounds are the two important types of compounds
• The constituent elements common in these compounds are carbon (C), hydrogen (H) and oxygen (O).
• The element carbon belongs to group 14 and its electronic configuration is 24. The valency of carbon is 4.

Bonds in carbon compounds :

→ Properties of carbon compounds :

• Carbon compounds have low melting and boiling points.
• These compounds are bad conductors of heat and electricity.
• The chemical bonds in carbon compounds do not produce ions.
• The force of attraction which holds the atoms together in a molecule is called a chemical bond.
• The number of chemical bonds that an atom of an element forms is called catenation power
• Ionic bonds and covalent bonds are the two important types of chemical bonds.

→ Bonds in carbon compounds :

 Carbon atom Electronic configuration Number of electrons in the Valence shell Nearby noble gas and the electronic configuration He Ne 6C 2, 4 4 2 2, 8

→ Carbon has 4 valence electrons and to attain the configuration of neon by sharing four valence electrons of other atoms. The shared electrons are accommodated in the overlapping region of valence shells of both the atoms.

→ As a result, both the atoms attain a noble gas configuration without generating any net charge on them, which means that atoms remain electrically neutral. Atoms attain stability due to these factors. Therefore this route is adopted by carbon atom to attain a noble gas configuration.

→ The chemical bond formed by sharing of two valence electrons between the two atoms is called covalent bond.

→ A covalent bond is clearly represented by drawing an electron-dot structure. In this method a circle is drawn around the atomic symbol and each of the valence electrons is indicated by a dot or a cross. The covalent bond formed between the atoms is indicated by showing the circles around the atomic symbols crossing each other.

→ The shared electrons are shown in the overlapping regions of the two circles by dot or cross. The electron-dot structure is also drawn without showing the circle. One covalent bond constitutes one pair of shared electrons. A covalent bond is also represented by a small line joining the symbols of the two atoms. The line structure is also called structural formula.

Carbon : A versatile element :

→ Carbon: A versatile element : In short, the entire living kingdom is made from carbon. Carbon is the basic ingredient of our body. Millions of molecules ranging from the small and simple methane molecule to the extremely big D.N.A. molecule are made from carbon. The molecular masses of carbon compounds range up to 1012.

 Carbon Compound Molecular mass Methane CH4 (The smallest carbon compound) 16 Cooking gas (C3H8 + C4H10) 44/58 Benzene (C6H6) 78 Camphor (C10H16O) 152 Penicillin (C16H18N204S) 334 Sugar (C12H22On) 342 Sodium dodecyl benzene sulphate (a detergent) 347 Fat ~ 700 Starch ~103 Cellulose ~105 Protein ~105 Polyethylene ~ 106 D.N.A. ~ 1012

Carbon compounds and molecular masses

Characteristics of carbon :

→ Carbon has a unique ability to form strong covalent bonds with other carbon atoms; this results in formation of big molecules. This property of carbon is called catenation power.

→ One, two or three covalent bonds can bond together two carbon atoms. These bonds are called single covalent bond, double covalent bond and triple covalent bond respectively. Example : ethane (CH3 – CH3). ethene (CH2 = CH2) and ethyne (CH = CH) which contain two carbon atoms.

→ Carbon being tetravalent, one carbon atom can form bonds with four other atoms (carbon or any other). This results in formation of many compounds. These compound possess different properties as per the atoms to which carbon is bonded.

→ For example, five different compounds are formed using one carbon atom and two monovalent elements hydrogen and chlorine : CH4, CH3Cl, CH2Cl2, CHCl3, CCl4 Similarly carbon atoms form covalent bonds with atoms of elements like O, N, Shalogen and P to form different types of carbon compounds in large number

→ Isomerism is one more characteristic of carbon compound which is responsible for large number of carbon compounds.

Hydrocarbons, functional groups and homologous series :

→ Saturated hydrocarbon : In hydrocarbon, the four valencies of carbon atom are satisfied only by the single bonds, such compounds are called saturated hydrocarbons. e.g. Ethane (C2H6), Propane (C3H8).

→ Unsaturated hydrocarbon : The carbon compounds having a double bond or triple bond between two carbon atoms are called unsaturated hydrocarbons.

→ The unsaturated hydrocarbons containing a carbon-carbon double bond are called alkenes. e.g. Ethene (CH2 = CH2), Propene (CH3 – CH = CH2)
The unsaturated hydrocarbons containing a carbon-carbon triple bond are called alkynes. e.g. Ethyne (CH = CH)

→ In the course of millions of years the reserves of crude oil were formed from the dead organisms buried under the sea floor. This crude oil and natural gas are now recovered from the oil wells. The natural gas is mainly methane.

→ The crude oil is a complex mixture of thousands of different compounds. It mainly contains various hydrocarbons. Various useful components such as CNG, LPG, petrol (gasoline), rockel, diesel, engine oil, lubricant, etc. are obtained by separating crude oil using fractional distillation.

→ Structural Isomerism : Butane is represented by two different compounds, as their structural formulae are different. These two different structural formulae have the same molecular formula, i.e. C4 H10

→ The closed chain of carbon atoms are present in some carbon compounds, wherein, rings of carbon atoms form. For example, the molecular formula of cyclohexane is CH and its structural formula contains a ring of six carbon atoms.

→ Benzene is a cyclic unsaturated hydrocarbon. There are three alternate double bonds in the six membered ring structure of benzene. The compounds having this characteristic unit in their structure are called aromatic compounds.

→ Functional group : The compound acquire specific chemical properties due to these hetero atoms or the groups of atoms that contain hetero atoms, irrespective of the length and nature of the carbon chain in that compound. Therefore, these hetero atoms or the groups of atoms containing hetero atoms are called functional groups.

→ Homologous series : The length of the carbon chains in carbon compounds is different, their chemical properties are very much similar due to the presence of the same functional group in them. The series of compounds formed by joining the same functional group in place of a particular hydrogen atom on the chains having sequentially increasing length is called homologous series. Two adjacent members of the series differ by only one – CH2 – (methylene) unit and their mass differ by 14 units.

Characteristics of Homologous series :

→ In homologous series while going in an increasing order of the length of carbon chain

• one methylene unit ( – CH2 – ) gets added
• molecular mass increases by 14 u
• number of carbon atoms increases by one.

→ Chemical properties of members of a homologous series show similarity due to the presence of the same functional group in them.

→ Each member of the homologous series can be represented by the same general molecular formula

→ While going in an increasing order of the length there is gradation in the physical properties, i.e. the boiling and melting points.

Nomenclature of carbon compounds :

→ IUPAC nomeclature system : International Union for Pure and Applied Chemistry (IUPAC) put forth a nomenclature system based on the structure of the compounds, and it was accepted all over the world. There are three units in the IUPAC name of any carbon compound : parent, suffix and prefix.

→ IUPAC name :
CH3 – CH2 – OH
Parent name: Ethane
Suffix: -OH (ol)
(functional group)
Parent suffix: Ethanol
IUPAC name: Ethanol.

Parent name: Pentane
Suffix: – OH (ol)
(functional group)
Assign numbering : 2

Parent suffix: Pentan – 2 – ol
IUPAC name: Pentan – 2 – ol.

• Methane is the component of biogas that makes it useful as fuel.
• Carbon dioxide is formed by the combustion of elemental carbon.
• The biogas combustion is exothermic reaction.

Chemical properties of carbon compounds :

Properties of carbon compounds:

→ Combustion : Methane undergoes combustion in the presence of oxygen to emit heat and light to form carbon dioxide and water.

→ Oxidation : Ethanol gets oxidised in the presence of alkaline potassium permanganate to form ethanoic acid.

→ Addition reaction : Vegetable oil (unsaturated compound) undergoes addition reaction with hydrogen in the presence of nickel catalyst to form vanaspati ghee (saturated compound).

→ Substitution reaction : The reaction in which the place of one type of atom/group in a reactant is taken by another atom/group of atoms, is called substitution reaction. Chlorination of methane, is a substitution reaction which gives four products.

→ Ethanol : Ethanol is a colourless liquid at room temperature and its boiling point is 78 “C. Generally ethanol is called alcohol or spirit. Ethanol is soluble in water in all proportions. When aqueous solution of ethanol is tested with litmus paper it is found to be neutral.

→ Ethanol being good solvent, it is used in medicines such as tincture iodine (solution of iodine and ethanol), cough mixture and also in many tonics.

→ Methanol (CH,OH), the lower homologue of ethanol, is poisonous, and intake of its small quantity can affect vision and at times can be lethal. To prevent the misuse of the important commercial solvent ethanol, it is mixed with the poisonous methanol. Such ethanol is called denatured spirit. A blue dye is also added to it, so that it is easily recognised.

→ Chemical properties of ethanol : Reaction with sodium

→ All the alcohols react with sodium metal to liberate hydrogen gas and form sodium alkoxide salts. When ethanol reacts with sodium metal, hydrogen gas and sodium ethaoxide are formed.

→ Dehydration reaction: When ethanol is heated at the temperature 170 C with excess amount of concentrated sulphuric acid, to form ethene, with elimination of water molecule.

Here, concentrated sulphuric acid acts as a dehydrating agent.

→ Ethanoic acid : Ethanoic acid is a colourless liquid with boiling point 118 °C. Ethanoic acid is commonly known as acetic acid. Its aqueous solution is acidic and turns blue limus red. Vinegar, which is used as preservative in pickles, is a 5-8% aqueous solution of acetic acid. The melting point of pure ethanoic acid is 17 °C. Therefore during winter in cold countries ethanoic acid freezes at room temperature itself and looks like ice. Therefore it is named ‘glacial acetic acid’.

Chemical Properties of ethanoic Acid :

Reaction with base :

→ A reaction with strong base Ethanoic acid gives neutralization reaction with a strong base sodium hydroxide to form a. salt and water.

→ Ethanoic acid reacts with sodium carbonate to form sodium ethanoate, water and carbon dioxide.

→ Esterification reaction : Ethanoic acid reacts with ethanol in presence of an acid catalyst, ethyl ethanoate (ester) is formed. This reaction is known as esterification.

→ Esters have sweet odour. Esters are used for making fragrances and flavouring agents. Saponifaction: When an ester is reacted with the alkali sodium hydroxide, the corresponding alcohol and sodium salt of carboxyclic acid are obtained.

→ This reaction is called saponification reaction, as it is used for preparation of soap from fats. Ester + Sodium hydroxide → Sodium Carboxylate + Alcohol

→ When fat is heated with NaOH solution, soap and glycerin are obtained.

Macromolecules and polymers :

Macromolecules and polymers:

• Macromolecules : The giant carbon molecules formed from hundreds of thousands of atoms are called macromolecules.
• Natural macromolecules : Polysaccharides, proteins and nucleic acid and rubber, etc.
• Manmade macromolecules: Elastomers, plastic, nylon, etc.
• Polymers: A macromolecule formed by regular repetition of a small unit is called polymer. The small unit that repeats regularly to form a polymer is called monomer. The reaction by which monomer molecules are converted into a polymer is called polymerization.

→ Various polymers and their uses:

→ The polymer’s in the above examples are formed by repetition of single monomer. These are called homopolymers. The other type of polymers are formed from two or more monomers. They are called copolymers.

→ For example, PET is poly ethylene terephthalate. The structures of polymers are linear as in the above examples or they are branched and cross linked as well. Polymers aquire various properties as per the nature of the monomers and the type of structure.

→ Some natural polymers and their occurrence :

Metallurgy Science Notes

Physical properties of metals :

Physical properties of nonmetals :

Properties of metals :

• Solid state (Exception : Mercury and gallium)
• Typical lustre
• Malleability and ductility
• Hardness (Exception : Lithium, sodium and potassium)
• Good conductors of heat and electricity
• High melting and boiling points (On the other hand, the melting and boiling points of the metals sodium, potassium, mercury and galium are very low.)
• Sonorous and produce sound on striking a hard surface.

Properties of nonmetals:

• Gaseous or solid state (Exception : Bromine in liquid state)
• Lack of any typical lustre (Exception : lodine and Diamond)
• Brittleness in the solid state (Exception : Diamond is the hardest natural substance)
• Bad conductors of heat and electricity (Exception: Graphite) (Diamond is good conductor of heat)
• Low melting and boiling points.

Chemical properties of metals :

→ Reaction of metals with oxygen : Metals combine with oxygen on heating in air and metal oxides are formed. Sodium and potassium are highly reactive metals. Sodium metal combines with oxygen in the air at room temperature to form sodium oxide.
4Na(s) + O2(g) → 2Na2O(s)

→ Sodium readily catches fire on keeping exposed to air producing a lot of heat. Therefore, to prevent accident in the laboratory or elsewhere it is kept in kerosene.

→ Sodium oxide reacts with water to form sodium hydroxide (alkali)
Na2 O(s) + H2O(l) → 2NaOH(aq)

→ Magnesium ribbon burns in air form magnesium oxide.

→ Reaction of metals with water : Sodium and potassium react vigorously with water to evolve hydrogen. Calcium reacts with water less vigorously to evolve hydrogen. Magnesium reacts with hot water to evolve hydrogen. Aluminium, iron and zinc do not react with cold or hot water but they react with steam to evolve their oxides and hydrogen.

→ Reaction of metals with acids : Metals react with dilute hydrochloric acid or dilute sulphuric acid to form metal chloride or metal sulphate and hydrogen gas. The rate of evolution of Hy is maximum in case of magnesium. The reactivity decreases in the order Mg > Al > Zn > Fe.

→ Reaction of metals with nitric acid : Metals react with nitric acid to form nitrate salts. Depending on the concentration of nitric acid, various oxides of nitrogen (NO, NO2,) are formed.

→ Aqua Regia: Aqua Regia is freshly prepared by mixing concentrated hydrochloric acid and concentrated nitric acid in the ratio 3 : 1. Aqua Regia is a highly corrosive and fuming liquid. It is one of the few reagents which can dissolve the noble metals like gold and platinum.

→ Reactions of metals with salts of other metals : The reactivity of all metals is not the same. All metals do not react with oxygen, water and acids. As a result, the relative reactivity of metals cannot be determined using these reagents. If a metal A displaces another metal B from the solution of its salt, it means that the metal A is more reactive than the metal B. Metal A+ Salt solution of metal B → Salt solution of metal A + Metal B.

Reactivity series of metals :

→ Reactivity series of metals : The arrangement of metals in the increasing or decreasing order of reactivity is called the reactivity series of metals. Metals are divided into the following groups according to their reactivity.

• Highly reactive metal.
• Moderately reactive metals.
• Less reactive metals.

Chemical properties of nonmetals :

→ Reaction of metals with nonmetals : The ionic compound is formed when metal reacts with nonmetal.

→ Ionic compound is formed as sodium loses one electron while chlorine accepts one electron. Reaction of nonmetals with oxygen: Nonmetals combine with oxygen to form acidic oxides. In some cases, neutral oxides are formed.

→ Reaction of nonmetals with water : Non metals do not react with water, (Exception-Halogen). Chlorine dissolves in water giving the following reaction.

→ Reaction of dilute acid with nonmetals: Nonmetals do not react with dilute acids, (Exception-Halogen). Chlorine reacts with dilute hydrobromic acid to form bromine and HCI.

Cl2(g) + 2HBr(aq) → 2HCl(aq) + Br2(aq)

→ Reaction of nonmetals with hydrogen : Nonmetals react with hydrogen under certain conditions such as proper temperature, pressure and use of catalyst.

S + H2 → H2S(g)
N2 + 3H2 → 2NH3(g)

Ionic compounds :

→ Ionic compounds : The compounds formed from two units, i.e. cation and anion are called ionic compounds. An electrostatic force of attraction between oppositely charged ions (cations and anions) is called an ionic bond.

General properties of ionic compounds:

• Ionic compounds are crystalline solids have a definite shape and hard due to strong electrostatic force of attraction between oppositely charged ions.
• They are generally brittle. When pressure is applied they break into pieces.
• They have high melting and boiling points.
• They are soluble in water and insoluble in solvents such as kerosene and petrol.
• They conduct electricity in the molten state and also in an aqueous solution.

Metallurgy : Various concepts :

→ Minerals and ores : The compounds of metals that occur in nature along with the impurities are called minerals. The minerals from which metals are extracted economically are called ores.

→ Metallurgy: The process of extraction of metal in pure form from the ores. The metals are further purified by different methods of purification. All this process is called metallurgy.

→ Concentration of ores : The process of separating gangue from the ores is called concentration of ores. Some general methods of concentration of ores as follows:

→ Separation based on gravitation : The gravitational method is used to separate the heavy particles of ores from the light particles of gangue. The processes to do this separation are as follows:

• Wilfey table method (Separation based on gravitation)
• Hydraulic separation method.
• Magnetic separation method
• Froth floatation method
• Leaching

→ When a metal loses electrons the process is called an oxidation while when a nonmetal gains electrons, it is called a reduction,
Na → Na+ + e (oxidation)
Cl + e → Cl (reduction)

→ Extraction of reactive metals : The extraction of highly reactive metals has to be done by electrolytic reduction.

→ Extraction of aluminium : Atomic number: 13, Electronic configuration : 2, 8, 3, Valency: 3. Aluminium is extracted from its main ore bauxite (Al2O3nH2O).
Extraction of aluminium involves the following steps:

• Concentration of bauxite ore (Hayer’s process)
• Electrolytic reduction of pure alumina
• Refining.

→ Concentration of bauxite ore : Powdered bauxite is heated with NaOH under high pressure and at 140 °C to 150 °C for 2 to 8 hours in a digester Al2O3 being amphoteric in nature forms sodium aluminate (NaAlO2) which is water soluble. The iron oxide impurities does not dissolve in aqueous NaOH and are separated by filtration.

→ However, silica reacts with sodium hydroxide to form soluble sodium silicate. NaAlO2 is hydrolysed to form insoluble Al(OH) by diluting it with water and cooling to 50 °C. Aluminium hydroxide precipitate is then filtered, dried and calcinated by heating at 1000 °C to obtain pure alumina.

→ Electrolytic reduction of alumina : Cell – A steel tank with graphite lining: Electrolyte – Alumina dissolved in fused cryolite; Cathode – The graphite (carbon) in the form of lining of the steel tank; Anode – Graphite (carbon) rods dipped in the electrolyte; cryolite (Na3AlF6) and fluorspar (CaF2) are added in the mixture to lower its melting point up to 1000°C.

→ Electrolysis products: Cathode – Aluminium metal, Anode – Oxygen gas.

At the anode : 2O2- → O2 + 4e
At the cathode : Al3+ + 3e → Al

→ Extraction of moderately reactive metals : In metals, in the middles of the reactivity series such as iron, zinc, lead, copper are moderately reactive. These metals occur in the form of their sulphide salts or carbonate salts.

→ The sulphides ores are strongly heated in air to convert them into oxides. This process is called roasting. Carbonate ores are strongly heated in a limited supply of air to convert them into oxides. This process is called calcination.

→ The following reaction occur during roasting and cacination of zinc ore.
Roasting : 2ZnS +3O2 → 2ZnO + 2SO2
Calcination: ZnSCO3 → ZnO + CO2
The zinc oxide is reduced to zinc by using suitable reductant such as carbon.
ZnO + C → Zn + CO↑

→ Extraction of less reactive metals : The less reactive metals are at the bottom of reactivity series of metal. These metals are found in free state in nature. For example, gold, silver, platinum. The reserves of copper in free state are exhausted long ago. Copper is found mainly in the form of Cu,s. Copper is obtained from Cu S ore just by heating in air.
2Cu2S +3O2 → 2Cu2O + 2SO2
2Cu2O + Cu2S → 6Cu + SO2

→ Refining of metals : Metals obtained by various reduction processes contain impurities Electrolysis method is used to remove impurities to obtain pure metals.

→ Corrosion is degradation of a material due to reaction with its environment.
When old iron bars in the buildings are exposed to moist air for a long time, they acquire a coating of brown flaky substance called rust. (Fe2O3.H2O)

→ If copper vessels are not cleaned for a long time, they react with moist carbon dioxide in the air, lose their shine and gain a green coat of copper carbonate. (CuCO3)

→ When silver ornaments or idols are kept exposed to air for a long time, silver reacts with sulphur in the air to form a coating of black silver sulphide. (Ag2S)

→ The metallic parts of the body of old cars are corroded, eaten up and sometimes become perforated. The old cars also lose the original colour due to formation of flakes of rust.

Prevention of corrosion :

→ By coating with some substance on the metal surface so that the contact of the metal with moisture and oxygen in the air is prevented and no reaction would occur between them.

→ By applying a layer of paint, oil, grease or varnish on the surface of a metal to prevent corrosion. For example, corrosion of iron can be prevented by this method.

→ Corrosion is prevented by coating a corrosive metals with a noncorrosive metal. This can be done in many ways:

• Galvanizing
• Tinning
• Anodization
• Electroplating
• Alloying.

Lenses Science Notes

Important Points :

→ Indicate the following terms related to spherical mirrors in figure 7.1 : pole, centre of curvature, radius of curvature, principal focus.

→ The given part of a hollow spherical glass can be converted into a concave mirror by

• polishing (silvering) its inner side (inner surface or concave surface) to make it reflecting or
• coating its outer side with a thin layer of silver and painting it with red colour to protect the silver coating.

[Note: Case (i) corresponds to the front surface silvered concave mirror.

→ The given part of a hollow spherical glass can be converted into a convex mirror by

• polishing (silvering) its outer side (outer surface or convex surface) to make it reflecting or
• coating its inner side with a thin layer of silver and painting it with red colour to protect the silver coating.

Note : Case (1) corresponds to the front surface silvered convex mirror

Lenses :

Lens : A lens is a transparent material bound by two surfaces, out of which at least one surface is spherical

→ Convex lens: A lens having both spherical surfaces puffed up outwards is called a convex lens or double convex lens or biconvex lens. A lens having one surface plane and the other (spherical surface) bulging outward is called a planoconvex lens.

→ A convex lens is thicker in the middle than at the edges. It is a converging lens. The concavo-convex lens has one spherical surface concave and the other convex such that it behaves as a convex lens.

→ Concave lens: A lens having both spherical surfaces curved inwards is called a concave lens or double concave lens or biconcave lens. A lens having one surface plane and the other (spherical surface) curved inwards is called a plano-concave lens.

→ A concave lens is thicker at the edges than in the middle. It is a diverging lens. The convexo-concave lens has one spherical surface convex and the other concave such that it behaves as a concave lens.

→ Centre of curvature (C) of a lens : The centres of the spheres whose parts form the surfaces of a lens are called the centres of curvature of the lens. A lens has two centres of curvature C, and C for its two spherical surfaces.

→ Radii of curvature (R, R) of a lens : The radii of the spheres whose parts form surfaces of a lens are called the radii of curvature of the
lens.

→ Principal axis of a lens : The imaginary straight line passing through the two centres of curvature of a lens is called the principal axis of the lens.

→ Optical centre (O) of a lens : The point inside a lens on the principal axis, through which light rays pass without changing their path is called the optical centre (O) of the lens.

→ Principal focus (F) of a lens : When light rays parallel to the principal axis are incident on a convex lens, they converge at a point on the principal axis. This point is called the principal focus (F) of the convex lens.

→ Light rays travelling parallel to the principal axis of a concave lens diverge after refraction in such a way that they appear to be coming out of a point on the principal axis. This point is called the principal focus of the concave lens. A lens has two principal foci F, and F.

→ Focal length of a lens : The distance between the optical centre and the principal focus of a lens is called the focal length of the lens.

Ray diagram for refracted light :

→ Rules for obtaining an image formed by a convex lens:

• When the incident ray is parallel to the principal axis, the refracted ray passes through the principal focus.
• When the incident ray passes through the principal focus, the refracted ray is parallel to the principal axis.
• When the incident ray passes through the optical centre of the lens, it passes without changing its direction.

[Note: Here, a ray means a ray of light.]

→ Image formation by a convex lens:

 Position of the object Position of the image Size of the image (relative to the size of the object) Nature of the image At infinity At focus F2 Point image Real and inverted Beyond 2FX Between F2 and 2F2 Smaller Real and inverted At 2FX                   ‘ At 2F2 Same size Real and inverted Between Fx and 2FX Beyond 2F2 Larger    _ Real and inverted At focus Fx At infinity Very large Real and inverted Between Fx and O On the same side of the lens as the object Very large Virtual and erect

[Note: In this chapter, no distinction is made between the terms focus and principal focus. Focus is also called focal point.]

→ An image formed by convergence of reflected or refracted rays of light at a point is called a real image.
An image formed at a point from which the reflected or refracted rays of light appear to diverge is called a virtual image.

→ A real image can be obtained on a screen. A virtual image cannot be obtained on a screen. Thus, if an image can be obtained on a screen, it must be real; if it cannot be obtained on a screen, it must be virtual. This is how we can find out whether an image is real or virtual.

→ Rules for obtaining an image formed by a concave lens:

• When the incident ray is parallel to the principal axis, the refracted ray, when extended backwards, passes through the principal focus.
• When the incident ray is directed towards the principal focus Fy, the refracted ray is parallel to the principal axis.
• When the incident ray passes through the optical centre of the lens, it passes without changing its direction.

→ The image formed by a concave lens is always virtual, erect and smaller than the object. It is on the same
side of the lens as the object. Generally, it is formed between the optical centre of the lens and the principal focus F1. If the object is at infinity, the image is a point image formed at F1.

 Position of the object Position of the image Size of the image (relative to the size of the object) Nature of the image At infinity On the first focus Fx Point image Virtual and erect Anywhere between optical centre O and infinity Between optical centre and focus Fx Small Virtual and erect

→ According to the Cartesian sign convention, the pole (P) of a spherical mirror is taken as the origin and the principal axis is taken as X-axis of the coordinate system.

• The object is always placed on the left of the mirror.
• All distances parallel to the principal axis are measured from the pole of the mirror.
• All distances measured to the right of the origin (pole) are taken as positive while distances measured to the left of the origin (pole) are taken as negative.
• Distances measured perpendicular to and above the principal axis are taken as positive.
• Distances measured perpendicular to and below the principal axis are taken as negative.
• The focal length of a convex mirror is positive while that of a concave mirror is negative.

Sign convention :

→ Sign convention for a lens : In this case, the optical centre (O) of the lens is taken as the origin and the principal axis of the lens is taken as X-axis of the coordinate system. The sign conventions regarding the measurement of distances parallel to the principal axis and those perpendicular to the principal axis are the same as for a spherical mirror. Hence, the focal length of a convex lens is positive and that of a concave lens is negative.

→ Lens formula: The relationship between the object distance (u), image distance (v) and focal length of a lens is called the lens formula and is given as $$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$$

→ Magnification by a lens : The magnification (M) produced by a lens
= $$\frac{\text { height of the image }\left(h_{2}\right)}{\text { height of the object }\left(h_{1}\right)}=\frac{v}{u}$$

Magnification is positive for a virtual image and negative for a real image.

→ Power of a lens : The power (P) of a lens
= $$\frac{1}{\text { focal length }(f) \text { of the lens }}$$
Its SI unit is the dioptre (D).
If f = 1 metre, P = 1 dioptre.

→ Combination of lenses : If two lenses with focal lengths f1 and f2 fare kept in contact with each other, the effective focal length of the combination, f, is given by $$\frac{1}{f}=\frac{1}{f_{1}}+\frac{1}{f_{2}}$$

→ The effective power of the combination of the lenses, P, is given by P = P1 + P2, where
p = $$\frac{1}{f}$$, P1 = $$\frac{1}{f_{1}}$$ and P2 = $$\frac{1}{f_{2}}$$

Working of the human eye and lens :

→ Power of accommodation of the eye : The ability of the eye lens to adjust its focal length is called the power of accommodation of the eye.

→ The minimum distance of distinct vision and the near point: The minimum distance from the normal eye at which an object is clearly visible without stress on the eye is called the minimum distance of distinct vision. It is 25 cm for the normal human eye.

→ The position of the object at the minimum distance of distinct vision is called the near point of the eye. For a normal human eye, the near point is at 25 cm from the eye.

→ The minimum distance of an object from a normal eye, at which it is clearly visible without stress on the eye, is called as minimum distance of distinct vision. The position of the object at this distance is called the near point of the eye, for a normal human eye, the near point is at 25 cm.

→ The farthest distance of an object from a human eye, at which it is clearly visible without stress on the eye is called farthest distance of distinct vision. The position of the object at this distance is called the far point of the eye For a normal human eye, the far point is at infinity.

→ The eye ball is approximately spherical and has a diameter of about 2.4 cm. The working of the lens in human eye is extremely important. The lens can change its focal length to adjust and see objects at different distances. In a relaxed state, the focal length of healthy eyes is 2 cm. The other focus of the eye is on the retina

Defects of vision and their correction :

→ Myopia or Nearsightedness : Myopia or near sightedness is the defect of vision in which a human eye can see nearby objects distinctly but is unable to see distant objects clearly. In this case, the image of a distant object is formed in front of the retina. This defect can be corrected using a concave lens of suitable focal length.

→ Hypermetropia or Farsightedness: Hypermetropia or farsightedness is the defect of vision in which a human eye can see distant objects distinctly but is unable to see nearby objects clearly. In this case, the image of a nearby object would fall behind the retina. This defect can be corrected using a convex lens of
suitable focal length.

→ Presbyopia (also called old age hyper metropia): Presbyopia is the defect of vision in which aged people find it difficult to see the nearby objects comfortably and clearly without spectacles. This defect can be corrected using a convex lens of suitable focal length.

Uses of lenses :

→ Uses of a convex lens : Simple microscope, compound microscope, telescope, camera, projector, spectrometer, spectacles, etc., make use of one or more convex lenses. A simple microscope is used by watch repairers, Jewellers, etc. A compound microscope is used to observe bacteria, cells, microorganisms, etc. A telescope is used to observe distant terrestrial objects or astronomical objects like planets, stars and comets.

→ Uses of a concave lens: A concave lens is used in spectacles to correct myopia. It is also used in optical instruments.

→ Persistence of vision: The image of an object remains imprinted on our retina for $$\frac{1}{16}$$th of a second after the object is removed from the sight. The sensation on the retina persists for a while. This is called persistence of vision. The retina in our eyes is made of many light sensitive cells. Due to these cells, we get information about the brightness or dimness of the object as well as the colour of the object