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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

→ 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 :

  • NADH2 – Nicotinamide Adenine Dinucleotide
  • 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.

Life Processes in Living Organisms Science Notes

→ 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 :

Life Processes in Living Organisms Science Notes 1

→ Anaerobic respiration in living organisms/cells.

Life Processes in Living Organisms Science Notes 2

→ 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.

Life Processes in Living Organisms Science Notes

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.

Life Processes in Living Organisms Science Notes

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

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes 3

→ 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.

Life Processes in Living Organisms Science Notes

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.


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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes 4

  • 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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes 5

→ 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

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

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.

Life Processes in Living Organisms Science Notes

→ 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.



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.

Life Processes in Living Organisms Science Notes

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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

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.

Life Processes in Living Organisms Science Notes

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.

Life Processes in Living Organisms Science Notes

→ 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.

Life Processes in Living Organisms Science Notes

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.

Science Notes