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Class 10 How do Organisms Reproduce? notes: NCERT Science Chapter 7 revision

CMDLearn · 3 November 2026

These are short revision notes for Chapter 7 of the NCERT Class 10 Science textbook (Reprint 2026-27). The chapter runs from page 113 to page 127. These notes:

• follow the book's sections in order;
• list the key words;
• describe the one diagram you should be able to draw;
• end with the mistakes students make most often.

Keep the textbook open next to these notes. The wording here is our own; the textbook is the authority.

How much it counts

CBSE's Class 10 Science curriculum for 2026-27 puts this chapter in Unit II, World of Living, worth 25 of the 80 theory marks. Unit II also includes Life Processes, Control and Coordination, and Heredity.

CBSE gives marks per unit, not per chapter, so no one can honestly give you an exact mark count for this chapter alone. For this chapter the unit lists:

• asexual and sexual reproduction in plants and animals;
• reproductive health, including why family planning is needed and its methods;
• safe sex and HIV/AIDS;
• childbearing and women's health.

More on the units: CBSE Class 10 Science syllabus 2026-27.

1. Why copies are never exact (section 7.1)

• Living things of one kind look alike because their body designs are alike, and a body design is coded in the DNA in the cell nucleus. DNA is the information used to make proteins.
• So the central event of reproduction is copying the DNA. The copy also needs its own set of cell machinery, so in effect one cell divides into two.
• No chemical reaction in a cell is perfectly reliable, so each DNA copy can carry small changes. A change that is too drastic kills the new cell. Smaller ones survive, so the new cells are alike but not identical.
• Why variation matters (7.1.1). A population survives because it fits its place (its niche) in the ecosystem, and accurate copying keeps that fit. But niches can change: temperatures rise or fall, and water levels move.
• If every individual were identical, one big change could wipe out the whole population. A few variants may survive instead.
• The book's example: if warming heats the water, a few heat-tolerant bacteria survive while the rest die.
• Variation helps the species last over time. It does not necessarily help each individual.

2. Asexual reproduction: one parent (section 7.2)

How an organism reproduces depends on its body design. Every method in this section makes new individuals from a single parent, which is what asexual reproduction means.

Why vegetative propagation is used:

• the new plants flower and fruit sooner than plants grown from seed;
• plants that no longer make seeds can still be grown;
• every new plant carries all the parent's characteristics.

Tissue culture (a box in 7.2.5, page 118) grows new plants from cells taken from a growing tip:

1. The cells are grown in an artificial medium until they form a mass called a callus.
2. The callus is moved to a second medium with hormones, where it grows and forms plantlets.
3. The plantlets go into the soil.

It gives many disease-free plants from one parent, and is common for ornamental plants.

Why complex organisms cannot just divide. Their cells form tissues, and their tissues form organs that must sit in fixed places in the body. Dividing cell by cell would not rebuild that order (section 7.2.2).

3. Sexual reproduction: why two parents (section 7.3.1)

• Combining DNA from two individuals makes new mixes of variations much faster than copying errors alone.
• The problem it creates. If two complete sets of DNA simply joined, each generation would have twice as much DNA as the one before.
• The solution. Special cells in the reproductive organs are made by meiosis, a cell division that halves the chromosome number and the DNA. When two such germ-cells fuse, the normal amount is restored.
• Two kinds of germ-cell. In complex organisms the two germ-cells differ: - the female gamete is large and stores food; - the male gamete is small and usually able to move.

4. Sexual reproduction in flowering plants (section 7.3.2)

• Where the reproductive parts are: in the flower. - The stamen (male part) makes the yellowish pollen grains. - The pistil (female part, at the centre) has three parts: the ovary at the swollen base, the style in the middle and the stigma at the top, which may be sticky. - Inside the ovary are ovules, and every ovule contains one egg cell.
• Unisexual and bisexual flowers. - Unisexual flowers have stamens or a pistil, not both: papaya, watermelon. - Bisexual flowers have both: Hibiscus, mustard.
• Pollination is the transfer of pollen from the stamen to the stigma. - Self-pollination: within the same flower. - Cross-pollination: from one flower to another, carried by wind, water or animals.
• Fertilisation. A pollen tube grows from the pollen grain down through the style to the ovary. There the male germ-cell fuses with the female germ-cell, and the fused cell is the zygote (Fig. 7.8, page 121).
• After fertilisation: - the zygote divides to form an embryo inside the ovule; - the ovule grows a tough coat and becomes the seed; - the ovary ripens into the fruit; - the other flower parts (petals, sepals, stamens, style, stigma) often dry up and fall.
• Germination. Under the right conditions the embryo in the seed grows into a seedling (Fig. 7.9, page 121). - The seed's parts: the cotyledon (food store), the plumule (future shoot) and the radicle (future root).

5. Reproduction in human beings (section 7.3.3)

Puberty. In the early teens the body starts to change in new ways as the reproductive tissues mature; this period is called puberty.

• Some changes happen in both girls and boys: - thick hair in new places; - oily skin and pimples.
• Others differ: - girls: the breasts grow and periods begin; - boys: hair grows on the face and the voice cracks.
• The changes are slow, start at different ages in different people, and vary from person to person. They begin as general body growth slows down.

Male reproductive system (7.3.3 (a), Fig. 7.10, page 123):

• Sperm are made in the testes. The testes sit outside the abdomen in the scrotum, because sperm formation needs a temperature lower than normal body temperature.
• Testosterone, a hormone from the testes, controls sperm formation and brings about the changes boys see at puberty.
• The sperm's path. Sperm travel through the vas deferens, which joins a tube from the bladder; so the urethra carries both sperm and urine.
• The fluid. The seminal vesicles and the prostate gland add a fluid that carries the sperm and nourishes them.
• The sperm itself is mostly genetic material, with a long tail for movement.

Female reproductive system (7.3.3 (b), Fig. 7.11, page 123):

• Eggs are made in the ovaries, which also make hormones. At birth the ovaries already hold thousands of immature eggs. From puberty, one egg a month is released by one of the two ovaries.
• The egg's path. The egg travels down the oviduct (fallopian tube). The two oviducts lead into the uterus, which opens into the vagina through the cervix.
• Fertilisation happens in the oviduct. The fertilised egg (zygote) divides into a ball of cells, the embryo.
• Implantation and growth. The embryo is implanted in the uterus lining. Its body parts develop there and it becomes a foetus.
• The placenta is a disc set in the uterine wall: - it has villi on the embryo's side and blood spaces on the mother's side, which together give a large surface for glucose and oxygen to pass to the embryo; - wastes from the embryo pass the other way, into the mother's blood.
• Birth. Development takes about nine months, and the baby is born through rhythmic contractions of the uterus muscles.

If the egg is not fertilised (7.3.3 (c), page 124):

• The egg lives for about one day.
• The uterus lining, which had become thick and spongy to receive an embryo, slowly breaks down. It leaves the body through the vagina as blood and mucus.
• This menstruation happens roughly every month and usually lasts two to eight days.

6. Reproductive health (section 7.3.3 (d))

• Readiness. Reaching some sexual maturity is not the same as being ready, in body and in mind, for sex or for raising a child. Young people can face pressure from friends, family and others, which makes such choices hard.
• Sexually transmitted infections: - bacterial: gonorrhoea and syphilis; - viral: warts and HIV-AIDS. - A condom lowers, though it does not remove, the risk of passing on many of these infections.
• Contraception. The book groups the methods into four kinds:

• Sex ratio. Prenatal sex determination is banned by law. Illegal sex-selective abortion of female foetuses has made the child sex ratio fall sharply in some sections of society, and a healthy society needs the female-male sex ratio to be kept balanced.

Key words at a glance

• Fission: a single cell dividing; binary (into two) or multiple (into many).
• Regeneration: a whole organism growing from a cut piece; not the usual way to reproduce.
• Budding: a new individual growing out of the parent at one spot, then separating.
• Vegetative propagation: a new plant from a root, stem or leaf.
• Sporangium: the structure that holds spores.
• Meiosis: cell division that halves the chromosome number in germ-cells.
• Gamete (germ-cell): a sex cell; male (small, moving) or female (large, stores food).
• Zygote: the cell formed when two gametes fuse.
• Pollination: pollen reaching the stigma; self or cross.
• Placenta: the tissue in the uterine wall through which the embryo gets food and oxygen and gives up wastes.
• Menstruation: the monthly loss of the uterus lining when the egg is not fertilised.
• Contraception: methods to avoid pregnancy (barrier, hormonal, devices in the uterus, surgical).

The diagram to know: the longitudinal section of a flower

Fig. 7.7 on page 120 is the diagram this chapter asks for most. Draw it in pencil and label seven parts:

1. Sepal (the green outer leaves at the base);
2. Petal;
3. Anther and 4. filament, which together make the stamen;
4. Stigma, 6. style and 7. ovary, which together make the pistil.

Two checks:

• Bracket the groups. Put a bracket for the stamen (anther + filament) and one for the pistil (stigma + style + ovary), as the book does.
• Draw the ovary as the swollen base in the centre of the flower, with ovules inside.

If you are asked about fertilisation, the matching diagram is Fig. 7.8 (page 121). It shows a pollen grain on the stigma, with the pollen tube carrying the male germ-cell down to the female germ-cell in the ovary.

Mistakes that cost marks

1. Calling regeneration a normal way to reproduce. The book says most organisms do not depend on being cut up.
2. Mixing up binary and multiple fission. Amoeba and Leishmania split into two; Plasmodium splits into many at once.
3. Calling the hyphae of bread mould reproductive parts. The reproductive parts are the sporangia with spores inside.
4. Saying the seed comes from the ovary. The ovule becomes the seed; the ovary becomes the fruit.
5. Placing fertilisation in the uterus. In humans the sperm meets the egg in the oviduct; the embryo implants in the uterus afterwards.
6. Forgetting why the testes are outside the body. Sperm formation needs a lower temperature than the body's normal temperature.

Revise with questions

Test yourself next: Class 10 How do Organisms Reproduce?, 8 practice questions with answers. The next chapter in the same unit has its own notes: Class 10 Heredity notes. For timed practice, the free Class 10 revision papers include a Science paper laid out in 1, 2, 3 and 5-mark sections.

Where CMDLearn fits

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Sources

All checked on 3 November 2026.

• NCERT, Science, Textbook for Class X, Chapter 7 "How do Organisms Reproduce?" (Reprint 2026-27), printed pages 113-127: - DNA copying and variation, pages 113-114; - fission, page 115 (Fig. 7.1) and page 116 (Plasmodium, Fig. 7.2); - fragmentation, page 116; - regeneration and budding, pages 116-117 (Figs. 7.3, 7.4); - vegetative propagation, page 117, and Bryophyllum, page 118 (Fig. 7.5); - tissue culture and spore formation, page 118 (Fig. 7.6); - asexual reproduction defined, page 119; - why sexual reproduction and meiosis, pages 119-120; - flowering plants, pages 120-121 (Figs. 7.7, 7.8, 7.9); - puberty, pages 121-123; - male and female systems, pages 123-124 (Figs. 7.10, 7.11); - menstruation and reproductive health, pages 124-125. ncert.nic.in/textbook/pdf/jesc107.pdf
• CBSE, Science (086), Class X, 2026-27, curriculum: course structure and Unit II (pages 4-5). cbseacademic.nic.in/web_material/CurriculumMain27/SecPart1/Science_SecP1_2026-27.pdf

The facts, figure numbers and page numbers are from the textbook and the curriculum above. The notes, their wording and the order of the lists are our own.

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