How do Organisms Reproduce? Class 10 Science Notes

What How do Organisms Reproduce? is about

Weightage: This chapter is part of Unit II, World of Living, which carries 25 of the 80 theory marks together with Life Processes, Control and Coordination and Heredity.Source: CBSE Science syllabus 2026-27, Unit II World of Living

In real board papers: asked in 21 of the 21 board papers we hold (2023 to 2026), on average 6.7 marks per paper. See the questions

Key concepts

DNA copying and variation

NCERT section 7.1 Do Organisms Create Exact Copies of Themselves?

Reproduction is not needed to keep one organism alive, unlike nutrition or respiration, and it costs a lot of energy. Yet we notice a species only because it reproduces and makes many similar-looking individuals.

Why do offspring look like their parents? Body design is decided by the DNA in the chromosomes of the nucleus. DNA is the information for making proteins. If those instructions alter, the cell ends up building altered proteins, and over time the body design shifts. So the basic event in reproduction is making a copy of DNA. The cell also builds extra cellular apparatus, because a DNA copy with no cell around it could not run life processes. Then the cell divides into two.

No chemical reaction is perfectly reliable, so the copies carry small variations. Drastic ones kill the new cell; mild ones survive. Accurate copying keeps the body design that fits the population's niche, so populations stay stable. Variation lets a few individuals survive if the niche changes, for example if water warms up. It helps the species, not necessarily every individual.

Worked example

A population of bacteria lives in a pond of cool water. Over some years the water temperature rises sharply.

(a) Predict what happens to the population.
(b) Explain why variation is beneficial to the species but not necessarily to the individual.
(c) Why does consistent DNA copying help a population while its niche stays unchanged? (3 marks)

Try it first, then show the solutionSolution

1. (a) Most bacteria, suited only to cool water, die. A few variants that happen to resist heat survive and multiply, so the population carries on. — 1 mark
2. (b) Variations arise by chance in a few individuals and may be of no use to that individual; but when the niche changes, the few suitable variants survive and keep the species going. — 1 mark
3. (c) Consistent copying keeps the body design that suits the niche, so the offspring can use the same niche and the population remains stable. — 1 mark

Answer: Most of the bacteria die but heat-resistant variants survive and grow, so the species survives. Variation protects the species over time, not each individual. Accurate DNA copying keeps the body design suited to the niche, giving a stable population.

Fission

NCERT section 7.2.1 Fission

In a unicellular organism the whole body is one cell, so cell division itself makes new individuals. This is fission.

• Binary fission: one cell splits into two equal halves. Many bacteria and protozoa do this. In Amoeba the split can happen in any plane, because its body has no fixed orientation.
• Leishmania, which causes kala-azar, has a whip-like structure at one end. Its body is more organised, so binary fission takes place in a definite orientation in relation to that structure.
• Multiple fission: the malarial parasite Plasmodium divides into many daughter cells at the same time.

Yeast is also single-celled but behaves differently: it puts out small buds that separate and grow further. You see this in Activity 7.1, where yeast is added to sugar solution and kept warm for an hour or two.

In every case the DNA is copied first and then the cell is shared out, which is why daughter cells are so similar to the parent. In the practical you study prepared slides of binary fission in Amoeba and budding in yeast.

Worked example

A student is given three prepared slides. Slide P shows a single cell splitting into two equal parts. Slide Q shows one cell giving rise to many daughter cells at once. Slide R shows a small outgrowth attached to a single cell.

(a) Name the process seen in each slide.
(b) Name one organism that shows the process in Q and one that shows the process in R.
(c) How would binary fission in Leishmania differ from that in Amoeba? (3 marks)

Try it first, then show the solutionSolution

1. (a) P: binary fission; Q: multiple fission; R: budding. — 1 mark
2. (b) Q: Plasmodium (malarial parasite); R: yeast. — 1 mark
3. (c) Amoeba can split in any plane; Leishmania has a whip-like structure at one end, so it splits in a definite orientation in relation to that structure. — 1 mark

Answer: P is binary fission, Q is multiple fission (Plasmodium), R is budding (yeast). Amoeba divides in any plane, while Leishmania divides in a fixed orientation related to its whip-like structure.

Fragmentation, regeneration and budding

NCERT section 7.2.3 Regeneration

Multicellular organisms with simple bodies can still use simple methods.

• Fragmentation: Spirogyra, a green filament found in pond water (Activity 7.4), breaks into pieces when mature, and each piece grows into a new individual. This works because its filament does not show different tissues.
• Most multicellular organisms cannot divide cell by cell. Their specialised cells form tissues, tissues form organs, and organs must sit at fixed places in the body. So they need one cell type that can grow, multiply and make the other cell types.
• Regeneration: Hydra and Planaria can be cut into many pieces and each piece grows into a whole organism. Specialised cells multiply into a mass. Cells from this mass then turn into the various cell types and tissues step by step, in a fixed order; this ordered process is called development. Being cut into pieces is an accident, not something organisms rely on to produce offspring, so regeneration is not counted as reproduction.
• Budding: Hydra uses its regenerative cells to reproduce. Repeated cell division at one specific site forms an outgrowth, the bud. It grows into a tiny Hydra and detaches when fully mature.

Worked example

A Planaria is cut across its body into three pieces: X (head end), Y (middle) and Z (tail end).

(a) What will each piece become after some days? Name the process.
(b) Explain how this is brought about inside the pieces.
(c) A classmate says, 'Since Planaria can do this, it is a normal way of reproduction for all animals.' Correct this statement with a reason. (3 marks)

Try it first, then show the solutionSolution

1. (a) Each of X, Y and Z grows into a complete Planaria; the process is regeneration. — 1 mark
2. (b) Specialised cells in each piece multiply to form a mass of cells; cells from this mass then turn into the different cell types and tissues step by step, in a fixed order (development). — 1 mark
3. (c) Regeneration is not the usual way animals make offspring: being cut up is an accident that organisms do not rely on. Complex organisms also have tissues and organs at fixed positions, so most of them cannot rebuild a whole body from a piece. — 1 mark

Answer: X, Y and Z each become a complete Planaria by regeneration, through multiplying specialised cells followed by development. Regeneration is not a normal mode of reproduction, and complex animals with organised organs cannot regenerate whole bodies.

Vegetative propagation and spore formation

NCERT section 7.2.5 Vegetative Propagation

In many plants a root, stem or leaf can grow into a new plant under the right conditions. Most animals cannot do this, but plants can use it as a real way of reproducing.

• In Activity 7.5, potato pieces with a notch (bud) are compared with pieces without one; the buds are what give rise to shoots and roots. Buds in the notches along the leaf edge of Bryophyllum fall on soil and grow into new plants.
• Layering and grafting use this property to grow sugarcane, roses and grapes for farming.
• Advantages: the plants flower and fruit earlier than plants grown from seed; plants that have lost the ability to make seeds, such as banana, orange, rose and jasmine, can still be grown; and every new plant is a close copy of the parent, so it keeps the parent's features.

Spore formation is seen in bread mould, Rhizopus (Activity 7.2). The thread-like hyphae are not reproductive. The tiny blob-on-a-stick structures are sporangia, which hold spores. Each spore has a thick wall that protects it until it reaches a moist surface, where it grows into a new Rhizopus.

Worked example

Give reasons for the following. (3 marks)

(a) Banana and jasmine are grown by vegetative propagation and not from seeds.
(b) A farmer who grows roses by layering gets flowers earlier, and every new plant has the same features as the parent.
(c) Rhizopus spores stay alive on dry bread but start growing when the bread becomes moist.

Try it first, then show the solutionSolution

1. (a) Banana and jasmine have lost the capacity to produce seeds, so vegetative propagation is the way to grow new plants. — 1 mark
2. (b) Vegetatively raised plants flower and fruit sooner than seed-grown ones, and since each new plant is a close genetic copy of the parent, it keeps the parent's features. — 1 mark
3. (c) Each spore is covered by a thick wall that protects it; it begins to grow only when it comes into contact with a moist surface. — 1 mark

Answer: (a) They cannot make seeds. (b) Vegetative propagation gives earlier flowering and plants that keep the parent's characteristics. (c) The thick spore wall protects the spore until it reaches a moist surface.

Why sexual reproduction: gametes and halving of DNA

NCERT section 7.3.1 Why the Sexual Mode of Reproduction?

In asexual reproduction variation comes only from copying errors, and DNA copying is accurate enough that this is slow. Making copying less accurate would not help, because many copies would not work with the cell and would die.

Sexual reproduction speeds up variation in another way. Two individuals already carry different variations built up over generations, and since both are alive, these variations are not seriously harmful. Combining DNA from two individuals makes a new combination every time. That is why bulls alone cannot produce calves; both sexes are needed.

This creates a difficulty: if two full sets of DNA joined, each generation would have twice the DNA of the last, which would upset the control of the cell by DNA. The solution is special cell lineages in reproductive organs that make germ-cells with half the chromosomes and half the DNA, by a division called meiosis. When two germ-cells fuse, the normal number returns in the zygote.

As bodies became complex, germ-cells specialised: the female gamete is large and stores food; the male gamete is small and motile.

Worked example

(a) Suppose the germ-cells of an animal had the same amount of DNA as its body cells. What would happen over generations of sexual reproduction?
(b) How do organisms actually avoid this problem?
(c) Why is one gamete large and the other small and motile in complex organisms? (3 marks)

Try it first, then show the solutionSolution

1. (a) Each zygote would get two full sets of DNA, so the DNA would double in every generation, and this would disturb the control of the cellular apparatus by DNA. — 1 mark
2. (b) Special cells in reproductive organs divide by meiosis to form germ-cells with half the chromosomes and half the DNA; fusion of two such germ-cells restores the normal amount in the zygote. — 1 mark
3. (c) The zygote needs stored energy to grow into a body with specialised tissues, so the female gamete is large with food stores; the male gamete is small and motile so it can reach the female gamete. — 1 mark

Answer: Without halving, DNA would double each generation and upset cell control. Meiosis makes germ-cells with half the DNA, and fertilisation restores it. The female gamete stores food for the zygote; the male gamete is small and motile.

Sexual reproduction in flowering plants

NCERT section 7.3.2 Sexual Reproduction in Flowering Plants

In angiosperms the reproductive parts are in the flower. Stamens (male) and the pistil (female) contain the germ-cells; sepals and petals do not.

• Unisexual flowers have either stamens or pistil (papaya, watermelon). Bisexual flowers have both (Hibiscus, mustard).
• The stamen produces yellowish pollen grains in its anther.
• The pistil, in the centre, has three parts: the stigma at the top, which may be sticky; the long style; and the swollen ovary at the base. The ovary contains ovules, each with an egg cell.

Pollination is the transfer of pollen from anther to stigma: within the same flower it is self-pollination; from one flower to another it is cross-pollination, by wind, water or animals.

Once a pollen grain lands on a suitable stigma, it puts out a thin pollen tube that pushes down inside the style until it reaches the ovary. The male germ-cell fuses with the egg in the ovule: fertilisation, giving a zygote. The zygote divides into an embryo, the ovule gets a tough coat and becomes the seed, and the ovary ripens into the fruit. The embryo in the seed later grows into a seedling: germination.

Worked example

(a) Distinguish between self-pollination and cross-pollination, and name the agents of cross-pollination. (2 marks)
(b) A pollen grain from one mustard flower lands on the stigma of another mustard flower. Describe, in the correct order, the events that lead to the formation of seed and fruit. (3 marks)

Try it first, then show the solutionSolution

1. (a) Self-pollination: pollen is transferred from the anther to the stigma of the same flower. — ½ mark
2. Cross-pollination: pollen is transferred from the anther of one flower to the stigma of another flower. — ½ mark
3. Agents of cross-pollination: wind, water and animals. — 1 mark
4. (b) After landing on the stigma, the pollen grain sends out a thin tube that runs down inside the style until it meets the ovary. — 1 mark
5. The male germ-cell reaches the ovule and fuses with the egg cell (female gamete); this is fertilisation and forms the zygote. — 1 mark
6. The zygote divides to form the embryo; the ovule develops a tough coat and becomes the seed; the ovary grows and ripens into the fruit. — 1 mark

Answer: Self-pollination is within one flower, cross-pollination is between flowers (by wind, water or animals). After pollination: pollen tube grows through the style, the male germ-cell fuses with the egg in the ovule, the zygote forms the embryo, the ovule becomes the seed and the ovary becomes the fruit.

Puberty and the human reproductive systems

NCERT section 7.3.3 Reproduction in Human Beings

While the body is growing to adult size, its resources go mainly to growth. As general growth slows in early teens, reproductive tissues mature. This period is puberty.

• In both sexes: thick hair in armpits and the genital area, thinner hair on arms, legs and face, oily skin and pimples.
• Girls: breasts enlarge, nipple skin darkens, menstruation begins.
• Boys: thick facial hair, voice cracks, the penis sometimes becomes enlarged and erect.

These changes are slow, vary from person to person, and many act as signals of sexual maturity.

Male system: testes make sperms and testosterone, which regulates sperm formation and causes the changes in boys at puberty. Testes lie in the scrotum, outside the abdomen, because sperms form properly only at a temperature a little cooler than the inside of the body. Sperms pass along the vas deferens, which joins a tube from the urinary bladder; the urethra carries both sperms and urine. Seminal vesicles and the prostate add a fluid that eases transport and gives nutrition.

Female system: ovaries (eggs and some hormones), oviducts or fallopian tubes, uterus, cervix and vagina.

Worked example

(a) Why are the testes located outside the abdominal cavity in human males?
(b) Trace the path of sperms from where they are formed to the outside of the body.
(c) State the role of the seminal vesicles and the prostate gland. (3 marks)

Try it first, then show the solutionSolution

1. (a) Testes lie in the scrotum, outside the abdominal cavity, because sperms form properly only at a temperature a little cooler than the inside of the body. — 1 mark
2. (b) Testes → vas deferens → urethra (common passage for sperms and urine) → out through the penis. — 1 mark
3. (c) They add their secretions so that sperms are in a fluid, which makes their transport easier and also provides them nutrition. — 1 mark

Answer: Testes are in the scrotum because sperms need a slightly cooler temperature than the inside of the body. Path: testes, vas deferens, urethra, penis. Seminal vesicles and prostate add fluid for easy transport and nutrition of sperms.

Fertilisation, placenta and menstruation

NCERT section 7.3.3 Reproduction in Human Beings

A girl's ovaries hold thousands of immature eggs at birth. From puberty, one egg is released every month by one of the ovaries and is carried along the thin oviduct towards the uterus. The two oviducts join into the uterus, an elastic bag that opens into the vagina through the cervix.

Sperms enter through the vagina during intercourse and travel up to the oviduct, where fertilisation may happen. The zygote divides into a ball of cells, the embryo, which is implanted in the uterus lining. Every month the lining thickens and gets a rich blood supply, ready to nourish an embryo.

The placenta is a disc embedded in the uterine wall. Villi on the embryo's side are surrounded by blood spaces on the mother's side. This gives a large surface for glucose and oxygen to pass to the embryo and for its wastes to pass into the mother's blood. The embryo develops organs and becomes a foetus; birth comes after about nine months through rhythmic contractions of the uterus muscles.

If the egg is not fertilised, it lives about a day. The thick, spongy lining is not needed, so it breaks down and leaves through the vagina as blood and mucous: menstruation, roughly monthly, lasting about two to eight days.

Worked example

(a) Describe the events from the meeting of sperm and egg in the oviduct up to the formation of a foetus. (2 marks)
(b) Describe the structure of the placenta and explain how it suits its function. (2 marks)
(c) What happens to the uterus lining if the egg is not fertilised, and why? (1 mark)

Try it first, then show the solutionSolution

1. (a) The sperm fuses with the egg in the oviduct, forming the zygote; the zygote divides to form a ball of cells, the embryo. — 1 mark
2. The embryo is implanted in the thick, blood-rich lining of the uterus, where it grows and develops organs to become a foetus. — 1 mark
3. (b) The placenta is a disc embedded in the uterine wall, with villi on the embryo's side and blood spaces on the mother's side surrounding the villi. — 1 mark
4. The villi and blood spaces give a large surface area for glucose and oxygen to pass from mother to embryo and for wastes to pass from embryo to the mother's blood. — 1 mark
5. (c) The thick, spongy lining is no longer needed, so it breaks down and comes out through the vagina as blood and mucous (menstruation). — 1 mark

Answer: Zygote forms in the oviduct, divides into an embryo, is implanted in the uterus lining and grows into a foetus. The placenta's villi and blood spaces give a large surface for exchange of food, oxygen and wastes. Without fertilisation the lining breaks down as menstruation.

Reproductive health and contraception

NCERT section 7.3.3 Reproduction in Human Beings

Some sexual maturity does not mean the body or mind is ready for sex or for having and bringing up children. Pressures can come from friends, families and even government agencies, which makes choices hard.

Sexually transmitted diseases: bacterial ones such as gonorrhoea and syphilis, and viral ones such as warts and HIV-AIDS. A condom lowers, though it does not remove, the risk of passing on many of these.

Why contraception? Sex can always lead to pregnancy, which makes major demands on a woman's body and mind; if she is not ready, her health suffers. Methods:

• Barrier: condom on the penis or a similar covering in the vagina stops sperm reaching the egg.
• Hormonal: oral pills alter the body's hormones so that no egg leaves the ovary; altered hormones can bring side-effects.
• Devices in the uterus: loop or copper-T; may irritate the uterus.
• Surgical: blocking the vas deferens or the fallopian tube; safe in the long run, but poorly done surgery can cause infection.

Misuse of surgery for illegal sex-selective abortion of female foetuses lowers the child sex ratio, although prenatal sex determination is banned by law.

Worked example

Analyse each situation and state its likely outcome with a reason. (3 marks)

(a) A woman uses a copper-T. Is she protected against HIV-AIDS?
(b) A man's vas deferens is blocked by surgery. Can his partner become pregnant?
(c) A woman takes oral contraceptive pills and her doctor warns her about side-effects. Why?

Try it first, then show the solutionSolution

1. (a) No. A copper-T is placed in the uterus only to prevent pregnancy; it does not stop contact during the sexual act, so HIV-AIDS and other infections can still pass. A condom is needed to reduce that risk. — 1 mark
2. (b) No. With the vas deferens blocked, sperms cannot be transferred, so fertilisation cannot take place. — 1 mark
3. (c) The pills alter the body's hormones so that no egg leaves the ovary, so there is nothing for sperm to fertilise; altered hormones can also cause side-effects. — 1 mark

Answer: (a) Not protected; copper-T only prevents pregnancy. (b) No pregnancy, as sperm transfer is blocked. (c) Pills act on her hormones, and that can cause side-effects.

Science in real life: How do Organisms Reproduce?

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Topics in this chapter

• Modes of Asexual Reproduction
• Vegetative Propagation in PlantsComing soon
• Sexual Reproduction in Flowering Plants
• Human Reproductive System
• Reproductive Health and Family PlanningComing soon

How do Organisms Reproduce?: formulas and key facts

Basic event of reproduction

DNA copy + additional cellular apparatus, then the cell divides into two

Use when asked why DNA copying is essential or what reproduction involves at the cell level.

Source of variation

DNA copying is never absolutely accurate, so copies are similar but not identical

Use for assertion-reason questions on variation in asexual and sexual offspring.

Importance of variation

Consistent copying gives population stability; variation gives survival of the species when the niche changes

Use for 'variation helps the species, not the individual' and the bacteria-in-warming-water type of question.

Types of fission

Binary: one cell into two (Amoeba any plane, Leishmania definite orientation); Multiple: one cell into many at once (Plasmodium)

Use for difference questions and slide identification in the practical.

Organism and method pairs

Yeast and Hydra: budding; Spirogyra: fragmentation; Hydra and Planaria: regeneration; Rhizopus: spores; Bryophyllum: leaf buds

Use for MCQs that ask which organism shows which method.

Advantages of vegetative propagation

Earlier flowering and fruiting; grows seedless plants (banana, orange, rose, jasmine); offspring keep parent's characteristics

Use for 'why is vegetative propagation practised' questions; write all three.

Germ-cells

• •Made by meiosis
• •half the chromosomes and half the DNA of body cells
• •fusion restores the full amount in the zygote

Use to answer why the DNA does not double each generation.

Male and female gametes

Male gamete: small and motile; female gamete: large with food stores

Use when asked how gametes became specialised in complex organisms.

Parts of the pistil

1. 1.Stigma (top, may be sticky)
2. 2.style (middle, elongated)
3. 3.ovary (swollen base, contains ovules, each with an egg cell)

Use for flower diagrams and case questions.

Pollination

Transfer of pollen from anther to stigma; self (same flower) or cross (another flower, by wind, water or animals)

Always contrast with fertilisation in difference questions.

Fertilisation in plants

Male germ-cell from pollen fuses with the egg in the ovule → zygote

Happens after the pollen tube grows through the style to the ovary.

After fertilisation in plants

1. 1.Zygote
2. 2.embryo; ovule
3. 3.seed; ovary
4. 4.fruit; petals, sepals, stamens, style and stigma may fall off

Use in 3- and 5-mark process answers.

Path of sperms

1. 1.Testes
2. 2.vas deferens
3. 3.urethra
4. 4.penis; seminal vesicles and prostate add fluid

Use for tracing questions and functions of glands.

Path of the egg and site of fertilisation

1. 1.Ovary
2. 2.oviduct (fallopian tube, site of fertilisation)
3. 3.uterus
4. 4.cervix
5. 5.vagina

Use when asked where fertilisation and implantation occur.

Menstruation key facts

• •Unfertilised egg lives about one day
• •lining breaks down as blood and mucous
• •roughly monthly
• •lasts about 2 to 8 days

Use for 'why does menstruation occur' questions; link it to the monthly preparation of the uterus.

Contraceptive categories

Barrier (condom), hormonal (oral pills), device in uterus (loop, copper-T), surgical (block vas deferens or fallopian tube)

Only the condom also helps reduce spread of sexually transmitted diseases.

How do Organisms Reproduce?: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks How do Organisms Reproduce?

The question patterns to expect, and the method that works for each.

Tricks to remember How do Organisms Reproduce?

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Plenty from Plasmodium

  Binary = 2 (Amoeba any way, Leishmania one fixed way). Multiple = many: think 'Plasmodium makes Plenty'.

  Use it when: Instantly match the type of fission to the organism in MCQs and slide questions.

• Pistil from top to bottom

  'Sticky Straw Over' = Stigma, Style, Ovary, going from top to the swollen base.

  Use it when: Label the pistil correctly in the flower diagram and describe pollen tube growth in order.

• House and room

  The ovary is the house, the ovule is a room inside it. After fertilisation, the room becomes the seed and the house becomes the fruit.

  Use it when: Stops you mixing up ovule to seed and ovary to fruit.

• Sperm route: TVUP

  Testes, Vas deferens, Urethra, Penis. 'The Van Unloads Parcels', and the Prostate and Seminal vesicles pack the lunch (fluid and nutrition).

  Use it when: Trace the path of sperms and name the glands in 3-mark answers.

• Egg route: Only One Uterus Can Vary

  Ovary, Oviduct, Uterus, Cervix, Vagina. Fertilisation happens in the second O, the oviduct.

  Use it when: Place fertilisation and implantation in the right organ.

• Four ways to plan: Boys Help Dad Sweep

  Barrier, Hormonal, Device in uterus, Surgical.

  Use it when: List all four categories of contraception in a 3- or 5-mark answer.

How do Organisms Reproduce?: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In the board paper this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in How do Organisms Reproduce?

The slips examiners see most often, and what to write instead.

• ✗Mistake: Mixing up pollination and fertilisation

  Both happen in the flower one after the other, so students treat them as one event.

  Wrong working

  Pollination is the fusion of pollen with the ovule to form a seed.

  Right working

  Pollination is the transfer of pollen from anther to stigma. Fertilisation is the later fusion of the male germ-cell with the egg in the ovule, forming a zygote.

  ✓Do this: Remember: pollination is a journey (transfer), fertilisation is a fusion. Write both definitions side by side in difference questions.

  Usually costs: 1-2 marks in a difference question, and a step in a 5-mark process answer.

• ✗Mistake: Writing that fertilisation in humans happens in the uterus

  The uterus is where the baby grows, so students assume fertilisation also happens there.

  Wrong working

  Sperms reach the uterus where they fertilise the egg, and the zygote develops there.

  Right working

  Sperms travel up to the oviduct (fallopian tube), where fertilisation occurs; the embryo is later implanted in the uterus lining.

  ✓Do this: Fix the sequence: oviduct for fertilisation, uterus for implantation and growth.

  Usually costs: 1 mark in short answers; the whole sequence step in a 3-mark tracing question.

• ✗Mistake: Swapping ovule and ovary after fertilisation

  The two words look and sound alike.

  Wrong working

  After fertilisation the ovary becomes the seed and the ovule becomes the fruit.

  Right working

  After fertilisation the ovule becomes the seed and the ovary ripens into the fruit; the zygote forms the embryo inside the seed.

  ✓Do this: Use the house-and-room trick: the room (ovule) is the seed, the house (ovary) is the fruit.

  Usually costs: 1 mark each time it appears.

• ✗Mistake: Saying a copper-T protects against sexually transmitted diseases

  Students think any contraceptive gives full protection.

  Wrong working

  The woman uses a copper-T, so she is safe from HIV-AIDS.

  Right working

  A copper-T only prevents pregnancy; it does not protect against sexually transmitted diseases. A condom lowers, though it does not remove, the risk of many such infections.

  ✓Do this: Remember that only the barrier method also lowers the risk of infection.

  Usually costs: 1-2 marks in situation-based questions.

• ✗Mistake: Giving the wrong reason for testes lying in the scrotum

  Students guess 'for protection' or 'for space' instead of the reason in the text.

  Wrong working

  Testes are outside the body so that they are protected and have more space.

  Right working

  Testes are in the scrotum, outside the abdominal cavity, because sperms form properly only at a temperature a little cooler than the inside of the body.

  ✓Do this: Link 'scrotum' to 'cooler than body temperature' every time.

  Usually costs: 1 mark.

• ✗Mistake: Saying gametes have half the cells, or that sexual reproduction doubles DNA

  Students half-remember the idea of halving.

  Wrong working

  Gametes have half as many cells, and when two join the child has double DNA.

  Right working

  Each germ-cell has half the chromosomes and half the DNA of a body cell, made by meiosis; fusion of two restores the normal amount in the zygote.

  ✓Do this: Say 'half the chromosomes and half the DNA', name meiosis, and say the amount is restored, not doubled.

  Usually costs: 1-2 marks in 3-mark reasoning questions and assertion-reason items.

• ✗Mistake: Claiming asexual offspring are exact copies

  Students hear 'one parent' and assume no change at all.

  Wrong working

  In asexual reproduction offspring are identical to the parent because there is only one parent.

  Right working

  Asexual offspring are very similar but not absolutely identical, because DNA copying is not perfectly accurate; variation is just much less than in sexual reproduction.

  ✓Do this: Avoid the words 'exact' and 'identical'; use 'similar, with small variations'.

  Usually costs: 1 mark in assertion-reason questions.

NCERT exercise guide: How do Organisms Reproduce?

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

How do Organisms Reproduce?: previous year questions

• Asked in 21 of the 21 board papers we hold (2023 to 2026), on average 6.7 marks per paper; 73 questions in all, counting OR alternatives. In 4 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from How do Organisms Reproduce?

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every How do Organisms Reproduce? question, by year

Practice questions on How do Organisms Reproduce?

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Both fallopian tubes of a woman are blocked by surgery. Which statement about her is correct?
   (a) Sperms can still meet the egg in the oviduct, so she can become pregnant.
   (b) The egg cannot reach the uterus, so fertilisation cannot take place.
   (c) She is now protected against syphilis.
   (d) Her partner's sperms are no longer formed.

   Hint

   Think about what a blocked tube stops from travelling.

   Answer

   (b) The egg cannot reach the uterus, so fertilisation cannot take place. A blocked tube gives no protection against infections and has no effect on sperm formation in her partner.

2. Q2 · 3 marks · Short answerHarder board level

   (a) State two functions of the testes in human males. (b) Why are the testes placed in the scrotum? (c) Predict what could happen to sperm formation if the testes stayed inside the abdominal cavity, giving a reason.

   Hint

   Link the position of the testes to temperature.

   Answer

   (a) They form the male germ-cells, the sperms, and they secrete testosterone, which regulates sperm formation and causes the body changes boys show at puberty.

   (b) The scrotum lies outside the abdominal cavity, where it is a little cooler than inside the body, and sperms form properly only at this lower temperature.

   (c) Sperm formation would be affected, because the testes would be at normal body temperature, which is too warm for sperms to form properly.

3. Q3 · 1 mark · Assertion-reasonBoard level

   Assertion (A): The daughter cells formed when an Amoeba divides are similar to, but not always identical with, the parent.
   Reason (R): In Amoeba, the splitting of the cell during binary fission can take place in any plane.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

   Hint

   Check each statement first, then ask what actually causes variation.

   Answer

   (b) Both A and R are true but R is not the correct explanation of A. A is true because DNA copying is never absolutely accurate, so small variations appear. R is also true, but the plane of splitting has nothing to do with variation.

4. Q4 · 3 marks · Short answerHarder board level

   List the changes at puberty that are common to boys and girls, and two changes specific to each. Why does the body show sexual maturation at this age and not earlier?

   Hint

   Think about where the body's resources go while it is still growing fast.

   Answer

   Common changes: thick hair in the armpits and genital area, thinner hair on the arms, legs and face, and oily skin with pimples.

   Girls: breasts get larger, the skin of the nipples darkens, and menstruation begins. Boys: thick facial hair grows and the voice begins to crack.

   Reason: while the body is growing to adult size, its resources go mainly into growth. As general growth slows, the reproductive tissues begin to mature.

5. Q5 · 5 marks · Long answerHarder board level

   (a) Describe the different categories of contraceptive methods, giving an example and one limitation of each. (3 marks)
   (b) Give two reasons why a couple might adopt contraception, linking one reason to women's health and one to safe sex. (2 marks)

   Hint

   Group the methods by what they block: sperm, egg release, the uterus, or a tube.

   Answer

   (a) Barrier: a condom, or a similar covering worn in the vagina, stops sperm reaching the egg. It works only if used every time. Hormonal: oral pills stop eggs being released, but they can cause side-effects. Devices in the uterus: a loop or copper-T, which can irritate the uterus. Surgical: blocking the vas deferens or fallopian tubes, which is safe in the long run, but the surgery can cause infection if it is not done properly.

   (b) Pregnancy makes major demands on a woman's body and mind, so if she is not ready her health suffers. A condom also lowers, though it does not remove, the risk of sexually transmitted infections such as HIV-AIDS.

6. Q6 · 3 marks · Short answerBoard level

   In the practical on the embryo of a dicot seed, gram seeds are soaked overnight, kept under a wet cloth for a day and then cut open. (a) Why are the seeds soaked and kept moist? (b) Name the parts you would identify. (c) Which part forms the shoot and which forms the root?

   Hint

   Germination needs appropriate conditions.

   Answer

   (a) Moisture provides the conditions the embryo needs to begin germinating, and it softens the seed so it can be opened easily.

   (b) Seed coat, two cotyledons, plumule and radicle.

   (c) The plumule forms the shoot and the radicle forms the root.

7. Q7 · 3 marks · Short answerHarder board level

   Explain why sexual reproduction produces more variation than asexual reproduction. How do organisms prevent the DNA amount from doubling in every generation?

   Hint

   Think about combining the variations already present in two different living individuals.

   Answer

   Different individuals in a population carry different accumulated variations, and because these individuals are alive, those variations are not harmful. Sexual reproduction combines DNA from two such individuals, which creates new combinations faster than copying errors alone. Asexual reproduction depends on one parent's copying errors only.

   To stop the DNA doubling, special cells in the reproductive organs divide by meiosis to make germ-cells with half the chromosomes and DNA. Fusion of two such germ-cells restores the normal amount.

8. Q8 · 2 marks · Very short answerBoard level

   Distinguish between pollination and fertilisation in flowering plants, stating where each takes place.

   Hint

   One is a transfer and the other is a fusion.

   Answer

   Pollination is the transfer of pollen grains from the anther to the stigma, so it happens on the outside of the pistil. Fertilisation is the fusion of the male germ-cell (brought by the pollen tube) with the egg cell in the ovule, so it happens inside the ovary. Pollination comes first, and fertilisation follows it.

9. Q9 · 3 marks · Short answerHOTS / competency

   Surgery to remove an unwanted pregnancy is a medical method, yet the NCERT text warns about its misuse. (a) How is it misused? (b) Why is this harmful to society? (c) What has the law done about it?

   Hint

   Link the misuse to the female-male sex ratio.

   Answer

   (a) Some people misuse it for illegal sex-selective abortion of female foetuses.

   (b) Female foeticide lowers the child sex ratio in some sections of society, but a healthy society needs the female-male sex ratio to be maintained.

   (c) Prenatal sex determination has been prohibited by law.

10. Q10 · 3 marks · Short answerHOTS / competency

    Suppose you do Activity 7.6 with six money-plant pieces dipped in water. Three pieces each carry a leaf, and all three grow roots and fresh leaves within days. Three pieces are cut from between two leaves, and none of them grows. (a) What can you conclude? (b) Name the mode of reproduction. (c) Give one advantage to a gardener of raising plants this way.

    Hint

    Compare this with the potato pieces that had a bud and those that did not.

    Answer

    (a) Only pieces that include a leaf can grow into new plants; a bare piece of stem cut from between two leaves cannot. This matches the potato activity, where only pieces with a bud sprouted.

    (b) Vegetative propagation by stem.

    (c) Each new plant is a close copy of the parent, so it keeps the parent's features, and plants raised this way can flower and fruit earlier than those grown from seed.

11. Q11 · 5 marks · Long answerHarder board level

    (a) Why is DNA copying an essential part of reproduction? (2 marks)
    (b) State two advantages of sexual reproduction over asexual reproduction. (1 mark)
    (c) Explain how reproduction gives stability to the populations of a species, and why some variation is still needed. (2 marks)

    Hint

    Build a chain: DNA, proteins, body design, niche.

    Answer

    (a) DNA carries the information for making proteins, and proteins decide body design. Copying DNA passes this design to the offspring, so they resemble the parent. The copy must be made along with extra cellular apparatus, because a DNA copy without an organised cell could not carry out life processes.

    (b) It combines DNA from two individuals, creating new combinations of variations; and it generates variation faster than copying errors alone, which helps the species survive changes.

    (c) Consistent DNA copying keeps the body design that lets the population use its niche, so the population stays stable from generation to generation. But if the niche changes drastically, a population of near-identical individuals could be wiped out; a few variants may survive, so variation protects the species over time.

12. Q12 · 3 marks · Short answerHOTS / competency

    Imagine a farmer has one plant of a seed-producing flowering crop whose fruits are unusually sweet. He wants (i) many more plants with exactly this sweetness, and (ii) a few plants that might cope better if the summers in his area become hotter. Which method of raising plants would you advise for each aim? Justify each choice.

    Hint

    Copies versus new combinations.

    Answer

    (i) Vegetative propagation, such as layering or grafting from the sweet plant. New plants grown from its parts are close copies of it, so they keep its sweetness, and they also flower and fruit earlier than seed-grown plants.

    (ii) Growing plants from seeds formed by cross-pollination. Fertilisation combines DNA from two parents, so the seedlings carry new combinations of variations; if summers get hotter, a few of them may carry variations that help them survive.

    So copies keep a good feature, while variety gives a chance of survival when conditions change.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What is the basic event in reproduction?Show answer

   Making a copy of DNA, along with additional cellular apparatus, before the cell divides.

2. 2.Which organism shows multiple fission?Show answer

   Plasmodium, the malarial parasite.

3. 3.In which two organisms can a cut piece grow into a whole organism?Show answer

   Hydra and Planaria (regeneration).

4. 4.Name four plants grown vegetatively because they have lost the ability to produce seeds.Show answer

   Banana, orange, rose and jasmine.

5. 5.What are the blob-on-a-stick structures on bread mould?Show answer

   Sporangia, which contain spores of Rhizopus.

6. 6.Which cell division halves the chromosome number in germ-cells?Show answer

   Meiosis.

7. 7.Where does fertilisation occur in human females?Show answer

   In the oviduct (fallopian tube).

8. 8.Name two bacterial and two viral sexually transmitted diseases.Show answer

   Bacterial: gonorrhoea and syphilis. Viral: warts and HIV-AIDS.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you explain why offspring are similar but not identical to their parent?
• ☐Can you say why variation helps a species but not always an individual?
• ☐Can you match Amoeba, Leishmania, Plasmodium, yeast, Spirogyra, Hydra, Planaria, Rhizopus and Bryophyllum to their methods?
• ☐Can you give three advantages of vegetative propagation?
• ☐Can you explain the doubling problem and how meiosis solves it?
• ☐Can you draw and label a longitudinal section of a flower and pollen germinating on a stigma?
• ☐Can you trace the steps from pollen on stigma to seed and fruit without missing the pollen tube?
• ☐Can you trace the path of sperms and of the egg, and say where fertilisation happens?
• ☐Can you describe the placenta and explain why menstruation occurs?
• ☐Can you list the four types of contraception and say which one also reduces infection risk?

How do Organisms Reproduce?: frequently asked questions