How do Organisms Reproduce

This is the seventh chapter of NCERT's Class 10 Science textbook (pages 113–127 of the 2026-27 reprint; the contents page and the PDF agree). It has three parts — do organisms create exact copies of themselves? (7.1, with the importance of variation), modes of reproduction used by single organisms (7.2: fission, fragmentation, regeneration, budding, vegetative propagation, spore formation) and sexual reproduction (7.3: why it exists, flowering plants, and human beings including reproductive health) — with 7 activities, Figures 7.1–7.11, a ‘More to Know?’ box on tissue culture, three in-text ‘Questions’ boxes (12 questions), a summary and 11 exercise questions. The human sections are written clinically; this page keeps them that way.

• Neighbouring chapters: Control and Coordination (Chapter 6) introduced testosterone, oestrogen and the pollen tube's chemotropism, used again here. Heredity (Chapter 8, next) explains how the variations made here are passed on. In Class 12, Sexual Reproduction in Flowering Plants, Human Reproduction and Reproductive Health are live and go much deeper (double fertilisation, gametogenesis, the menstrual cycle's hormones, contraceptive methods and the laws); Principles of Inheritance and Variation and Human Health and Disease (HIV, sexually transmitted infections) are live too. This page links to them rather than re-teaching them.
• Prelims — science: UPSC has asked about grafting (1979, 2009), tissue culture (1985), what fruit and seed develop from (1998), fission in Amoeba (2005), where fertilisation happens in humans (2007), pollinating animals (2012) and vegetative propagation and clones (2014).
• GS3 — science, technology and agriculture: vegetative propagation and tissue culture in horticulture, pollinators and food security. GS1/GS2 — society and health: reproductive health, contraception, sexually transmitted diseases, the child sex ratio and population — summarised here and treated in depth on lebo102 and lebo103.

• Why reproduce? Not needed for an individual's life, but it keeps a species going. Basic event: DNA copying plus new cell apparatus. Copying is never exact → variation, which helps the species (not necessarily the individual) survive a changed niche — e.g. heat-resistant bacteria when water warms.
• Asexual, single parent: fission — binary in Amoeba (any plane) and Leishmania (set orientation; causes kala-azar), multiple in Plasmodium; budding — yeast, Hydra; fragmentation — Spirogyra; regeneration — Planaria, Hydra (not true reproduction); spores — Rhizopus sporangia.
• Vegetative propagation: roots, stems, leaves → new plants (Bryophyllum leaf buds, potato eyes, money-plant cuttings); layering, grafting for sugarcane, roses, grapes; earlier flowers and fruit; seedless banana, orange, rose, jasmine; offspring like the parent. Tissue culture: growing tip → callus → hormones → plantlets → soil.
• Sexual: two parents combine DNA → more variation. Meiosis halves chromosomes in germ cells, fertilisation restores them. Female gamete large with food store; male gamete small, motile.
• Flower: sepals, petals, stamens (anther + filament, pollen) and pistil (stigma, style, ovary with ovules). Unisexual: papaya, watermelon; bisexual: Hibiscus, mustard. Pollination (self/cross; wind, water, animals) → pollen tube → fertilisation → zygote → embryo; ovule → seed, ovary → fruit; seed germinates (plumule, radicle, cotyledons).
• Humans: puberty; testes in the scrotum (cooler) make sperms and testosterone → vas deferens → urethra, with seminal-vesicle and prostate fluid. Ovaries release one egg a month → oviduct (fertilisation) → uterus (implantation; placenta villi; about 9 months). No fertilisation → lining shed: menstruation, 2–8 days. Contraception: barrier, pills, copper-T/loop, surgery; STDs; sex-ratio concern.

Organisms of one kind look alike because their body designs are alike, and those designs come from similar blueprints. Class IX showed that the chromosomes in the nucleus carry the information for inheritance as DNA (deoxyribonucleic acid), and DNA is the information source for making proteins; changed information means different proteins and, eventually, altered body designs. So a basic event in reproduction is creating a DNA copy, by chemical reactions in the cell. Pushing the copy out of the cell would not work — it would have no organised structure to keep life going — so DNA copying goes with the creation of additional cellular apparatus, and then the copies separate, each with its own apparatus: one cell becomes two.

No biochemical reaction is absolutely reliable, so each copy may differ slightly from the original. A drastic change can leave the new DNA unable to work with the apparatus it inherits, and the new cell dies; many other changes are not drastic, so the surviving cells are similar but subtly different. This in-built tendency for variation is the basis for evolution. Why it matters (7.1.1): populations fill well-defined places, or niches, in an ecosystem, and consistent copying keeps the body design that suits the niche — so reproduction is linked to the stability of populations. But niches change beyond the organisms' control — temperatures rise or fall, water levels vary, meteorites hit. A population perfectly suited to one niche could be wiped out; if a few individuals vary, some may survive. NCERT's example: bacteria in temperate water — if global warming heats the water, most die, but the few heat-resistant variants survive and grow. Variation is useful for the survival of species over time.

The modes organisms use depend on their body design. For unicellular organisms, cell division — fission — creates new individuals, in several patterns. Many bacteria and protozoa simply split into two equal halves; in Amoeba the split can take place in any plane. Some single cells are more organised: Leishmania, which causes kala-azar, has a whip-like structure at one end, and its binary fission occurs in a definite orientation in relation to these structures. The malarial parasite Plasmodium divides into many daughter cells simultaneously — multiple fission. Yeast, by contrast, puts out small buds that separate and grow (Activity 7.1).

Fragmentation (7.2.2): in many-celled organisms with a simple body, simple methods still work. Spirogyra breaks up into smaller pieces when mature, and each fragment grows into a new individual — its filament is made of similar cells, without different tissues (Activity 7.4). Most many-celled organisms cannot divide cell by cell, because specialised cells are organised into tissues, tissues into organs, and organs must sit at definite places. Since different cell types do different jobs, reproduction too becomes the job of a specific cell type — one able to grow, multiply and make other cell types.

Regeneration (7.2.3): many fully differentiated organisms can give rise to new individuals from body parts. Simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism. It is carried out by specialised cells that multiply into a mass, from which cells change into various cell types and tissues in an organised sequence called development. But NCERT is explicit: regeneration is not the same as reproduction, since most organisms do not depend on being cut up to reproduce. Budding (7.2.4): Hydra uses its regenerative cells for reproduction — a bud develops as an outgrowth from repeated cell division at one specific site, grows into a tiny individual and, when mature, detaches as a new independent individual.

In many plants, parts like the root, stem and leaves develop into new plants under suitable conditions — vegetative propagation. Unlike most animals, plants can use this for reproduction. Farmers use it in methods such as layering or grafting to grow plants like sugarcane, roses or grapes. NCERT gives three advantages: such plants bear flowers and fruits earlier than those raised from seed; the methods allow propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds; and all the plants produced are genetically similar enough to the parent to have all its characteristics. In Bryophyllum, buds produced in the notches along the leaf margin fall on the soil and grow into new plants (Fig. 7.5); a potato's notches (‘eyes’) hold buds (Activity 7.5); a money-plant piece with a leaf grows roots (Activity 7.6).

Tissue culture (‘More to Know?’, page 118): tissue is removed, or cells separated, from the growing tip of a plant and placed in an artificial medium, where they divide rapidly into a small group of cells, the callus. The callus is moved to another medium containing hormones for growth and differentiation; the resulting plantlets are placed in soil to grow into mature plants. Many plants can be grown from one parent, in disease-free conditions; the technique is commonly used for ornamental plants.

Even in many simple many-celled organisms, specific reproductive parts can be seen. The threads that spread on bread in Activity 7.2 are the hyphae of the bread mould Rhizopus; they are not reproductive parts. The tiny blob-on-a-stick structures are: the blobs are sporangia, which contain cells, or spores, that can develop into new Rhizopus. Spores have thick walls that protect them until they meet another moist surface and can begin to grow. All the modes described so far create a new generation from a single individual — asexual reproduction.

Bulls alone cannot produce calves, nor hens chicks: both sexes are needed. Why? DNA copying makes variations, which protect the species, so modes that generate more variation make sense. Copying is precise enough that variation arises slowly; making it less accurate would kill many copies. But each individual already carries variations accumulated over generations, and since they are in living individuals they are not badly harmful. Combining DNA from two individuals creates new combinations — sexual reproduction does exactly this.

The difficulty: combining two parents' DNA would give each new generation twice the DNA of the last, upsetting the cell's control. The solution in many many-celled organisms is special lineages of cells in specialised organs that carry only half the number of chromosomes and half the DNA of body cells, made by a cell division called meiosis. When these germ cells from two individuals combine, the chromosome number and DNA content are re-established. A zygote that is to grow into a complex organism needs stored energy: in very simple organisms the two germ cells may look alike, but in complex ones one is large with food stores — the female gamete — and the other smaller and likely to be motile — the male gamete. This difference drives the differences between male and female reproductive organs and, sometimes, bodies.

The reproductive parts of angiosperms are in the flower: sepals, petals, stamens and pistil. Stamens and pistil contain the germ cells. A flower is unisexual if it has either stamens or pistil (papaya, watermelon) and bisexual if it has both (Hibiscus, mustard). The stamen is the male part and produces yellowish pollen grains. The pistil, in the centre, is the female part, with three parts: the swollen bottom ovary, the middle elongated style and the terminal, possibly sticky stigma. The ovary contains ovules, each with an egg cell. The male germ cell from the pollen grain fuses with the female gamete in the ovule — fertilisation — giving the zygote, which can grow into a new plant.

So pollen must reach the stigma. Transfer within the same flower is self-pollination; from one flower to another it is cross-pollination, achieved by agents such as wind, water or animals. On a suitable stigma, a tube grows out of the pollen grain and travels through the style to the ovary. After fertilisation the zygote divides several times to form an embryo within the ovule; the ovule develops a tough coat and becomes a seed; the ovary grows and ripens into a fruit; petals, sepals, stamens, style and stigma may shrivel and fall off. The seed holds the future plant, the embryo, which grows into a seedling under suitable conditions — germination.

Humans use sexual reproduction. Growth makes the body larger; but in the early teenage years changes begin that are not simple enlargement — sexual maturation. Common to boys and girls: thick hair in the armpits and genital area, thinner hair on legs, arms and face, oily skin and pimples, and new awareness of one's own and others' bodies. In girls, breasts grow, the skin of the nipples darkens, and menstruation begins. In boys, thick facial hair appears, the voice begins to crack, and the penis occasionally becomes enlarged and erect. The changes take months and years, do not happen at one exact age, and differ between people. Why at this age? While the body grows to adult size, maturing reproductive tissue is not a priority; as general growth slows, reproductive tissues mature — puberty. Many changes signal sexual maturity to others; the transfer of germ cells needs special organs, and in mammals the baby is carried for a long time and breast-fed, so the female organs and breasts must mature too.

Male system (7.3.3 a): parts that make germ cells and parts that deliver them. Sperms form in the testes, which lie outside the abdominal cavity in the scrotum because sperm formation needs a lower temperature than normal body temperature. The testes also secrete testosterone (Chapter 6), which regulates sperm formation and brings about the changes of puberty in boys. Sperms travel through the vas deferens, which unites with a tube from the urinary bladder, so the urethra is a common passage for sperms and urine. Along the way the prostate and seminal vesicles add secretions: the fluid eases transport and gives nutrition. Sperms are tiny, mostly genetic material, with a long tail to move towards the female germ cell. Female system (7.3.3 b): eggs are made in the ovaries, which also make some hormones. At birth a girl's ovaries already hold thousands of immature eggs; from puberty some mature, and one egg is produced every month by one of the ovaries. It is carried to the womb through a thin oviduct (fallopian tube); the two oviducts join an elastic, bag-like uterus, which opens into the vagina through the cervix.

During intercourse sperms enter through the vagina, travel upwards and reach the oviduct, where they may meet the egg. The fertilised egg (zygote) starts dividing into a ball of cells, the embryo, which is implanted in the lining of the uterus and grows organs to become a foetus. Since the uterus must be ready, it prepares every month: its lining thickens and is richly supplied with blood. The embryo gets nutrition from the mother's blood through the placenta, a disc embedded in the uterine wall. It has villi on the embryo's side and blood spaces on the mother's side surrounding them, giving a large surface area for glucose and oxygen to pass from mother to embryo; the embryo's wastes pass into the mother's blood. Development takes about nine months; the child is born by rhythmic contractions of the uterine muscles.

If the egg is not fertilised (7.3.3 c), it lives for about one day. Because the ovary releases one egg every month, the uterus prepares every month, its lining becoming thick and spongy. Not needed now, the lining slowly breaks and comes out through the vagina as blood and mucous. This happens roughly every month — menstruation — and usually lasts about two to eight days (NCERT).

Because sexual maturation is gradual and happens while the body is still growing, some maturation does not mean the body or mind is ready for sexual acts or for having and raising children. NCERT notes many pressures — from friends, from families to marry and have children, and from government agencies to avoid having children — that make choices difficult. Since the sexual act is an intimate connection of bodies, many diseases are sexually transmitted: bacterial (gonorrhoea, syphilis) and viral (warts, HIV-AIDS). A condom on the penis helps prevent many of these, to some extent.

Pregnancy makes major demands on a woman's body and mind; if she is not ready, her health suffers — so ways to avoid pregnancy, contraception, have been devised in several categories: mechanical barriers (condoms, or similar coverings in the vagina); hormonal methods, usually oral pills, that stop eggs being released (with possible side-effects); devices placed in the uterus — the loop or copper-T (side-effects from irritation of the uterus); and surgery to block the vas deferens in the male or the fallopian tube in the female (safe in the long run, but surgery done improperly can cause infections and other problems). Surgery can also remove unwanted pregnancies; this can be misused, as in illegal sex-selective abortion of female foetuses. NCERT says the female–male sex ratio must be maintained for a healthy society, notes that child sex ratio is declining at an alarming rate in some sections because of female foeticide, and that prenatal sex determination is prohibited by law. Finally, birth and death rates set population size; the book sets out two views on what matters most for living standards (table below) and asks the reader to think.

Short outlines in page order for the three ‘Questions’ boxes (12 questions), six questions asked in the running text, and the seven activities.

Numbers

One-liners

• Reproduction is not needed for the individual's life; it keeps the species going.
• Basic event: DNA copying plus new cell apparatus; copying is never exact → variation.
• Variation helps the species survive a changed niche, not necessarily the individual.
• Amoeba: binary fission in any plane; Leishmania: in a definite orientation; Plasmodium: multiple fission.
• Yeast and Hydra bud; Spirogyra fragments; Planaria regenerates; Rhizopus forms spores.
• Vegetative propagation: earlier fruit, seedless plants (banana, orange, rose, jasmine), offspring like the parent.
• Tissue culture: growing tip → callus → hormone medium → plantlets → soil; disease-free.
• Meiosis halves the chromosomes in germ cells; fertilisation restores them.
• Female gamete large with food; male gamete small and motile.
• Pollination (transfer) comes before fertilisation (fusion).
• Ovule → seed; ovary → fruit; cotyledons store food; plumule → shoot; radicle → root.
• Testes in the scrotum need a lower temperature; urethra carries both sperms and urine.
• Fertilisation in the oviduct; implantation in the uterus; nourishment through the placenta.
• Copper-T does not protect against STDs; condoms help to some extent.

Traps to avoid

• Fission (one cell divides) ≠ fragmentation (simple body breaks up on its own) ≠ regeneration (cut pieces regrow).
• Regeneration is listed in 7.2 but NCERT says it is not the same as reproduction.
• Budding in yeast is the answer to exercise 1, not Amoeba, Plasmodium or Leishmania.
• Ovule → seed, ovary → fruit — not the reverse.
• Vas deferens is male; fertilisation is in the fallopian tube, not the uterus.
• Vegetative propagation passes on plant viruses; tissue culture from growing tips gives disease-free plants.
• Gonorrhoea and syphilis are bacterial; warts and HIV-AIDS viral.
• NCERT slips: menstruation ‘2–8 days’ vs Class 12's 3–5; regeneration listed as a mode yet ‘not reproduction’; QR label 1064CH08 from the old numbering.

Prelims — what UPSC asks

• Asexual reproduction and horticulture: grafting two fruits on one plant (1979), tissue culture (1985), Amoeba's fission as assertion–reason (2005), sweet-orange grafting and jasmine layering (2009) and vegetative propagation's clonal, year-round nature (2014).
• Sexual reproduction: fruit from the ovary and seed from the ovule (1998), the fallopian tube as the site of fertilisation (2007), and bats, bees and birds as pollinators (2012). Sex determination, twins, IVF and the PNDT Bill sit on the Class 12 chapters.
• Likely next: modes matched to organisms (budding, fragmentation, multiple fission), clones and micropropagation, pollinator decline, the site of fertilisation and implantation, which contraceptives also protect against STIs, PCPNDT.
• Answer-key note (1985, ‘What is tissue culture?’): the stored key is (a) ‘preparation of fragments of the cells of organism for biochemical examination’. NCERT's tissue culture is growing new plants from cells in artificial media, which (a) does not describe, so (d) ‘none of the above’ is arguable. Treat the key as disputed (a/d); it is an old, loosely worded item.
• Answer-key note (2014, vegetative propagation): the stored key (c) ‘1 and 3 only’ stands — clonal (1) is right; ‘helps eliminate viruses’ (2) is wrong for ordinary vegetative propagation; ‘practised most of the year’ (3) is accepted.

Mains — where it appears and how to answer

• No GS Mains question in the bank so far is built on this chapter's core content. It supplies the biology for GS3 answers on horticulture (vegetative propagation, tissue culture, disease-free planting material), pollinators and food security, and for GS1/GS2 answers on the child sex ratio, female foeticide, reproductive and adolescent health and population.
• Answer frame: the biological mechanism in one line (meiosis and fertilisation; the copper-T in the uterus; tissue culture's callus) → the social or farm consequence → the law or programme (PCPNDT Act; Beti Bachao Beti Padhao; tissue-culture planting material) → positions on open questions, attributed, no verdict.
• A small sketch — the contraception route map or the pollen tube — fits in a 150-word answer.

Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.

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