Reproduction

A bud on a Hydra, a plantlet on a leaf and a seed inside a fruit can all begin a new individual. Yet they do not all begin in the same way. The useful question is: what is copied, what joins, and where does development happen?

These notes cover NCERT Class 10 Science, Chapter 7, How do Organisms Reproduce?, in the 2026–27 reprint. Reproduction and reproductive health remain in the current CBSE assessed course. Start with the new-plant detective workshop, then follow the same ideas from cells to flowers to human beings.

Why do organisms reproduce?

Nutrition and respiration help an existing organism stay alive. Reproduction produces new organisms. An individual can live without reproducing, but a population cannot continue indefinitely if no new individuals replace those that die. Reproduction connects generations; it is not a duty that every individual must fulfil.

The connection depends on inherited information. DNA, deoxyribonucleic acid, carries information used by cells to make proteins. Proteins help determine how cells develop and function. Chromosomes contain DNA; copying it helps transmit the organisation needed to build a similar organism. A DNA molecule alone is not a tiny ready-made organism: a new cell also needs a membrane, cytoplasm and functioning cellular machinery.

In a reproducing single-celled organism, copying the genetic material and dividing the cell can produce new individuals. In a human, most cell division supports growth or repair instead. A dividing skin cell does not become another person. Whether cell division counts as reproduction depends on what new biological individual is formed.

One cell becomes two. Has reproduction definitely happened?

For an Amoeba dividing into two independently living Amoebae, yes. For cells dividing inside a growing leaf, not necessarily: they usually remain parts of the same plant. Identify the organism before naming the process.

Why is there variation between individuals?

DNA copying is accurate enough to preserve much of a body plan, but occasional changes can occur. A change in DNA is a mutation. Some changes have little noticeable effect, some are harmful, and some can be useful under particular conditions. A copying event does not inevitably change every DNA molecule, and a new variant is not automatically an improvement.

Imagine a population of bacteria in water that becomes warmer. If some already possess inherited features that help them tolerate the new conditions, they may survive and reproduce more successfully. The heat does not instruct the bacteria to make exactly the mutation they need. Variation gives a population different possibilities; it guarantees neither an individual's survival nor the population's escape from extinction.

Sexual reproduction also reshuffles inherited variants into new combinations. This explains why offspring can resemble their parents without being identical to either. Similarity and variation work together: sufficient continuity allows a functioning body to develop, while differences provide material on which selection can act over generations. The detailed inheritance of traits belongs in Heredity.

Types of reproduction

Asexual reproduction forms offspring without the fusion of gametes. Offspring usually develop from one parent's cells and are genetically very similar to that parent. Mutation can still introduce differences. Sexual reproduction involves the fusion of two gametes, or reproductive cells, to form a zygote.

“One parent versus two parents” is a useful first comparison, but gamete fusion is the stronger test. A self-fertilising plant can supply both kinds of gamete itself and still reproduce sexually. Conversely, joining two plant parts in a graft is not the fusion of gametes.

• Asexual routes: can multiply a successful form without finding a mate; many plants and simple animals use them.
• Sexual routes: combine inherited material through gametes and usually generate a wider range of genetic combinations.
• The trade-off: speed, resources, available partners and environmental conditions matter. Neither route is universally better, and “simple” and “advanced” are not rankings of an organism's worth.

Modes of asexual reproduction

Fission: divide a whole cell

In binary fission, one parent cell gives rise to two daughter cells after its genetic material has been copied. Amoeba can divide in different planes. Leishmania has a more definite body organisation, including a flagellum, so its division follows a definite orientation relative to that structure. In multiple fission, as in stages of the Plasmodium life cycle, one cell produces many daughter cells. “Binary” describes the number of daughters, not a fixed direction of division.

Fragmentation and regeneration: similar outcomes, different questions

A mature Spirogyra filament can break into pieces, each capable of growing into a new filament under suitable conditions. This is fragmentation. Its relatively simple organisation makes growth from such pieces possible.

Regeneration is the rebuilding of missing parts through cell division and organised development. Planarians can regenerate complete animals from suitable body fragments. The retained cells must produce and organise different tissues in the right places. This capacity has limits: it does not mean that every piece of every animal, however small, becomes a complete organism.

Regeneration can contribute to reproduction in some organisms, but ordinary repair is not automatically reproduction. A lizard replacing a lost tail has not made a second lizard. Complex organs and their connections cannot generally be recreated merely by separating arbitrary cells.

Budding: grow an offshoot

In yeast, a small outgrowth develops on a parent cell and can separate as a new cell. In Hydra, repeated cell division at a particular site produces a bud. The bud develops a small body with tentacles and eventually detaches. The parent does not first split into two similar-sized halves: watch the outgrowth develop before separation.

Vegetative propagation: a new plant from an existing plant part

Some roots, stems and leaves can produce new plants. Potato “eyes” are buds on a stem tuber; ginger is also a modified stem. Bryophyllum develops plantlets from buds along leaf margins. Stored food can support initial growth, but food alone does not explain the result: the appropriate growing tissue matters.

Gardeners use cuttings, layering and grafting to propagate plants. In a cutting, a suitable detached piece develops roots and shoots. In layering, a stem forms roots while still attached to the parent. In grafting, a shoot called the scion is joined to a compatible rooted stock. Grafting joins living tissues; it does not blend their DNA into a sexually produced hybrid.

Vegetative propagation can preserve a desirable variety and often gives a shorter wait for flowering than starting from seed. It is especially useful for varieties that produce few or no viable seeds. That is a statement about particular varieties, not a claim that every orange or rose is seedless. Genetic similarity can be useful commercially while also leaving a crop vulnerable if many plants share susceptibility to the same disease.

In NCERT's enrichment box on tissue culture, cells or small pieces of tissue are grown on an artificial nutrient medium under controlled conditions. Dividing cells can form a callus; suitable growth regulators encourage shoots, roots and differentiated tissues. Plantlets are then established outside the culture. CBSE excludes information in textbook boxes from year-end assessment; it remains useful for understanding the biology. Clean conditions help prevent contamination; tissue culture is not a promise that any starting material is automatically free of every pathogen.

Design a fair test: is a potato eye important?

Compare several similar-sized pieces with an eye and several without a visible eye. Keep water, temperature, light and observation time comparable. Record new shoots separately from decay. If only eye-bearing pieces sprout, the result supports the importance of the bud under those conditions. A single failed piece could have dried out: repeated observations make the explanation stronger. Use photographs or a teacher's prepared observations if cutting is not appropriate.

Spore formation: protected cells that can travel

Rhizopus, a bread mould, forms thread-like hyphae and sporangia that contain spores. When released, spores can disperse; their protective walls help them survive until conditions permit growth. A spore is a reproductive cell, not a seed containing a plant embryo. The visible mould threads and the spore-producing structures have different roles. Prepared images are sufficient for this comparison; there is no need to grow or handle mouldy food.

Sexual reproduction

Why gametes have a reduced chromosome set

If two full body-cell chromosome sets simply combined in each generation, the chromosome number would keep doubling. Meiosis produces cells with a reduced chromosome set; gametes carry one set rather than the two sets typical of many body cells. When two gametes fuse at fertilisation, the zygote regains the usual paired set. Subsequent cell division and differentiation build the organism.

The sperm is generally small and adapted to delivering genetic material; the egg is larger and supplies substantial cell contents for early development. Size does not measure the importance of either gamete's inherited contribution. In flowering plants, pollen carries the male reproductive cells; a whole pollen grain is not simply another name for a sperm.

Read a flower by its jobs

A typical flower has protective sepals, petals that can help attract pollinators, stamens and a pistil. A stamen consists of a filament and an anther, where pollen develops. The pistil includes the stigma, style and ovary. The stigma receives pollen; the style connects it to the ovary; the ovary contains ovules, each with an egg cell in the chapter's model.

A bisexual flower contains stamens and pistil, as in the familiar Hibiscus and mustard examples. A unisexual flower has stamens or pistil, as in the flowers discussed for papaya and watermelon. This describes a flower's reproductive parts, not a rule that every plant bears both types of flower.

Pollination is arrival; fertilisation is fusion

1. Transfer: pollen moves from anther to stigma. This is pollination. Wind, water or animals can act as carriers, depending on the plant.
2. Delivery: compatible pollen germinates on a receptive stigma. A pollen tube grows through the style towards an ovule, carrying male gametes.
3. Fusion: a male gamete fuses with the egg inside the ovule. This fertilisation forms a zygote.
4. Development: the zygote develops into an embryo. The ovule develops into a seed, while the ovary usually develops into the fruit. Some other flower parts may persist.
5. A new growing plant: with suitable water, oxygen and temperature, a viable seed can germinate into a seedling. Different species have additional requirements.

In self-pollination, pollen reaches the same flower or another flower on the same plant. Cross-pollination brings pollen from a different plant of the same species. NCERT introduces the distinction using “same flower” and “another flower”; the OpenStax account makes the same-plant case explicit. Self-pollination can still lead to gamete fusion, so it is not vegetative propagation.

Pollination does not guarantee fertilisation, and fertilisation does not guarantee a mature seed. Compatibility, successful development and growing conditions matter. The flower workshop asks you to separate what an observation shows from what still needs evidence.

A fruit contains several seeds. Did several ovaries have to join?

No. One ovary can contain several ovules. In the simple flower model, each successfully developing fertilised ovule can become a seed within the fruit. Do not confuse the enclosing ovary with an individual ovule. Real fruits vary, including fruits formed from multiple flowers or flower parts; the model does not cover every fruit type.

Inside a dicot seed

A gram, pea or bean seed contains an embryo protected by a seed coat. Its two cotyledons are seed leaves; in these examples they hold food that supports early growth. The radicle develops into the root, while the plumule develops into the shoot. Germination continues the growth of an embryo already present in the seed; it is not a new fertilisation event. CBSE practical work includes identifying these parts, alongside prepared-slide comparisons of fission in Amoeba and budding in yeast and Hydra.

Reproduction in human beings

Puberty: change is gradual and variable

Puberty is the period when hormonal changes lead towards reproductive maturity. It overlaps with general growth rather than waiting for growth to finish. Common changes include new hair growth in the armpits and pubic region, oilier skin and changes in feelings. Breast development and the beginning of menstruation occur in the typical female pattern; increased facial hair and a deeper voice occur in the typical male pattern. Erections can occur without a deliberate decision.

These changes do not all start at the same age, follow an identical timetable or look the same in every person. Reproductive organs also vary in appearance. Physical maturity is different from emotional readiness, consent or the ability to care for a child. Learning the anatomy does not require anyone to discuss their own body or experiences.

Male reproductive system: make, support and transport sperm

• Testes: produce sperm and secrete testosterone, which contributes to sperm production and pubertal changes.
• Scrotum: holds the testes outside the abdominal cavity, helping maintain the lower temperature needed for sperm formation.
• Epididymis and vas deferens: sperm mature in the epididymis and are transported through the vas deferens.
• Seminal vesicles and prostate: add secretions that support sperm and help form semen, the fluid in which sperm travel.
• Urethra and penis: semen passes through the urethra and can be delivered into the vagina during sexual intercourse. In this anatomy the urethra also carries urine, but sperm are not made in the bladder.

A sperm has a head containing genetic material and a tail that helps movement. Sperm and semen are not synonyms: sperm are cells; semen contains sperm together with glandular fluids. On NCERT's male-system diagram, trace the vas deferens independently of the tube carrying urine from the bladder.

Female reproductive system: release an egg and support development

• Ovaries: contain immature egg cells from before birth. From puberty, some mature; usually one egg is released during an ovulatory cycle. The ovaries also produce hormones including oestrogen and progesterone.
• Oviducts or fallopian tubes: receive the released egg and carry it towards the uterus. Fertilisation usually occurs in an oviduct if a sperm meets and fuses with the egg.
• Uterus: has a lining in which an embryo can implant and develop. It is not the organ that makes eggs.
• Cervix and vagina: the cervix is the narrow lower part of the uterus, with a canal opening into the vagina. The vagina receives semen and provides a passage for menstrual flow and, during vaginal birth, the baby.

After sperm enter the vagina, some may travel through the cervix and uterus towards an oviduct. Fertilisation creates a zygote. As it divides and travels towards the uterus, it develops into an early embryo. Implantation means attachment within the uterine lining; it is a later event than the fusion of gametes. The developing organism forms organs and is later described as a foetus.

The placenta forms an exchange interface at the uterine wall. Villi provide a large surface area: oxygen and nutrients pass towards the developing embryo or foetus, while carbon dioxide and other wastes pass towards the mother's circulation. Maternal and foetal blood normally remain in separate circulations across this interface. The umbilical cord connects the foetus to the placenta; it is not a food pipe from the mother's stomach.

Development takes approximately nine months. Rhythmic contractions of uterine muscles contribute to childbirth. The chapter describes the basic process; it is not a guide to managing pregnancy or birth.

What happens when the egg is not fertilised?

The menstrual cycle coordinates changes in the ovaries and uterine lining through hormones. Ovulation is the release of an egg. If pregnancy does not occur, levels of oestrogen and progesterone fall and much of the thickened uterine lining is shed. Blood and tissue pass through the cervix and vagina: this is menstruation. The period is part of the cycle, not the name for every event in it.

The cycle is counted from the first day of one period to the first day of the next. A 28-day diagram is a teaching example, not a clock every body must obey. Cycle length and bleeding duration vary, especially in the years after periods begin. Menstrual flow is not “dirty blood”, and the visible bleeding is not simply the tiny egg leaving the body. The Office on Women's Health explanation distinguishes the lining, hormones and cycle clearly.

Watch with a question: in TED-Ed's How menstruation works, how do hormones connect changes in the ovaries with changes in the uterine lining? Its 28-day cycle and lifetime totals are illustrative, not personal rules or current population statistics. The short time an egg remains available for fertilisation is also not the same as the time in which intercourse could lead to pregnancy: sperm can survive for several days, and ovulation varies. Compare the animation's final discussion of variation with the NHS explanation; do not treat the animation as a contraceptive calendar.

Repair three mixed-up labels

“An egg is made in the uterus; fertilisation happens in the vagina; implantation happens in the ovary.” Replace them with ovary → oviduct → uterine lining. Each location does a different job. The arrow is a functional sequence, not a diagram of organ size or a claim that pregnancy always follows ovulation.

Reproductive health

Reproductive health involves reliable information, informed choices, respectful relationships and access to appropriate care. Family planning helps people decide whether and when to have children and how to space pregnancies. Pregnancy and child-bearing make physical and emotional demands; preventing an unintended pregnancy can protect health and educational opportunities. Responsibility belongs to partners and society, not solely to women.

Two different goals: prevent pregnancy and reduce infection

Sexually transmitted infections include bacterial infections such as gonorrhoea and syphilis, and viral infections such as HIV and infections with some types of human papillomavirus that cause genital warts. HIV stands for human immunodeficiency virus; AIDS, acquired immunodeficiency syndrome, is the most advanced stage of HIV disease. HIV is not spread by ordinary contact such as hugging or sharing food. People living with HIV deserve care and respect, not exclusion.

WHO's current HIV explanation describes effective treatment and routes of transmission. This distinction matters scientifically: identifying a pathogen and its transmission route is more useful than treating every contact as dangerous.

• Condoms: a barrier helps keep sperm from reaching an egg. Correct, consistent use also reduces the risk of most STIs, including HIV. Protection is not absolute; infections involving uncovered skin can still be transmitted.
• Hormonal contraceptives: pills and other methods alter reproductive processes, for example suppressing ovulation or making cervical mucus harder for sperm to pass. They do not provide STI protection.
• Intrauterine devices: an IUD is placed in the uterus by a trained health worker. A copper IUD releases copper ions that interfere with sperm movement and fertilisation. It is not a condom or a plug across the vagina, and it does not protect against STIs.
• Sterilisation: vasectomy interrupts the vas deferens; tubal surgery blocks or interrupts the fallopian tubes. These methods prevent gametes meeting and are intended as permanent contraception. They do not remove the testes or ovaries and do not provide STI protection.

Methods differ in suitability, side effects and reversibility. The mechanism table explains biology; a qualified health professional helps with personal choices. Contraception prevents pregnancy; abortion ends an existing pregnancy. They should not be combined into one “surgical contraception” category. No procedure instructions are needed to understand the distinction.

Evaluate a health-poster claim

A poster says: “A copper IUD prevents pregnancy, so it also prevents HIV.” The conclusion does not follow. Copper changes conditions affecting sperm and fertilisation; it does not create the barrier needed to reduce exposure to infected fluids. WHO explicitly states that IUDs do not protect against STIs. Name the outcome and mechanism separately before accepting a health claim.

NCERT also raises discrimination linked to sex selection. India's PCPNDT Act prohibits sex selection and regulates prenatal diagnostic techniques to prevent their misuse. Tests for legitimate medical purposes should not be confused with choosing a child according to sex. Equal dignity is the underlying issue; no child's value depends on being male or female.

Why it still matters

A nursery choosing how to propagate a plant and a public-health team explaining contraception face a shared reasoning task: match a method to an intended result. A cutting can preserve a variety without producing a seed. Pollen reaching a stigma does not prove a seed will develop. Preventing pregnancy does not automatically prevent infection. Careful definitions have practical consequences.

Try a small source investigation. Read the diagrams in NCERT, the same-plant pollination paragraph from OpenStax and WHO's current IUD fact sheet. For each, write two lines: “This source shows…” and “It does not establish…”. A diagram explains a route; a comparison clarifies terminology; health evidence distinguishes outcomes. None is a substitute for all the others.

Population size also depends on deaths and migration, as well as births. Access to education, healthcare and resources affects people's lives; the number of people alone does not explain inequality. Discuss policy with evidence and respect for choice rather than assigning blame to families.

To check your understanding, explain asexual reproduction without saying “always identical”; trace a pollen grain and a male gamete separately; distinguish ovary, ovule and uterus; and describe menstruation without a fixed calendar. Continue with Class 10 Science or explore the wider study library.

Sources

Curriculum and source checks: 7 September 2026. The main explanation follows the current NCERT chapter; the further sources clarify particular scientific and health distinctions.

1. NCERT Science, Chapter 7: How do Organisms Reproduce? — 2026–27 reprint, printed pages 113–127; mechanisms, diagrams, activities and reproductive health.
2. CBSE Class 10 Science curriculum, 2026–27 — current reproduction, health and practical scope.
3. OpenStax Biology 2e: Pollination and fertilisation — university-published explanation clarifying self-pollination and pollen-tube delivery.
4. US Office on Women's Health: Your menstrual cycle — hormone changes, uterine lining and variation between cycles.
5. WHO: Family planning and contraception, IUDs and condoms — informed choice and the difference between pregnancy prevention and STI protection.
6. WHO: HIV and AIDS — infection, illness, transmission and effective treatment.
7. NICHD: About vasectomy and NCI: Epididymis — sperm transport and maturation.
8. Vascular Biology of the Placenta: Placental blood circulation — maternal and foetal circulations and exchange.
9. India Code: PCPNDT Act, 1994 — purpose and provisions addressing sex selection and misuse of prenatal diagnosis.

Key takeaways

• Reproduction produces new organisms to sustain populations, though individuals can survive without it.
• DNA carries inherited information that determines cell development and function, but a new organism requires more than just DNA.
• Cell division results in reproduction only if it produces a new independent biological individual, not just growth or repair.
• Variation arises from occasional DNA mutations or sexual reproduction reshuffling, providing raw material for natural selection but not guaranteeing survival.
• Asexual reproduction produces genetically similar offspring from one parent, while sexual reproduction involves gamete fusion and generates greater genetic diversity.

Test yourself

What is the primary purpose of reproduction for a population?

Reproduction produces new individuals to replace those that die, ensuring the population continues indefinitely.

How does DNA contribute to the formation of a new organism during reproduction?

DNA carries inherited information that guides cell development and function, but a new organism also requires a membrane, cytoplasm, and functioning cellular machinery.

When does cell division count as reproduction?

Cell division counts as reproduction only if it produces a new independent biological individual, such as in Amoeba, not when cells divide for growth or repair.

What is the difference between asexual and sexual reproduction?

Asexual reproduction forms offspring from one parent without gamete fusion, producing genetically similar offspring, while sexual reproduction involves gamete fusion and generates greater genetic diversity.

How does variation arise in populations?

Variation arises from occasional DNA mutations or the reshuffling of inherited variants during sexual reproduction, providing raw material for natural selection.