How do Organisms Reproduce Notes Class 10 Science
How do Organisms Reproduce?
Why this chapter matters
One amoeba becomes two. One seed becomes a banyan tree.
Every living thing copies itself, yet no two children are identical. This chapter explains both facts. You will learn how simple organisms multiply, how flowers make seeds, how a human baby grows, and how reproductive health protects families.
These Class 10 Science Chapter 7 notes cover the full syllabus prescribed by CBSE for the 2026–27 session.
Chapter Learning Map
Follow the spine top to bottom. Four groups, all equally important.
1 · Variation — why no two offspring are identical
Reproduction is the process by which an organism produces new individuals of its own kind. DNA, present in the nucleus, carries the instructions for building the body.
When a cell divides, it first makes a copy of its DNA. Each new cell receives one copy. This copying is very accurate, but never perfectly accurate. The small differences that appear are called variation.
Two bacteria in a pond differ slightly in heat tolerance. A heat wave kills almost all of them. The few with higher tolerance survive and multiply.
A cut on your skin heals because body cells divide and replace the damaged cells. The new cells carry the same DNA copy.
DNA copying is the blueprint. Variation is the insurance policy.
Reproduction does not make identical copies. It makes near-copies with small differences. Write “variation”, not “identical”.
Identical twins are the rare exception. They come from one fertilised egg, so their DNA is almost the same.
2 · Asexual reproduction — fission, fragmentation, regeneration
Asexual reproduction is reproduction by a single parent without gametes. The offspring are near-identical to the parent.
Single-celled and simple organisms use these methods. Each method is fast, and it needs only one parent.
| Mode | How it happens | Organism |
|---|---|---|
| Binary fission | Parent cell divides into two daughter cells | Amoeba, Leishmania, bacteria |
| Multiple fission | Parent cell divides into many cells at once | Plasmodium |
| Fragmentation | Body breaks into pieces; each piece grows | Spirogyra (filamentous algae) |
| Regeneration | A cut body part grows into a full organism | Planaria, Hydra, starfish |
An Amoeba grows, copies its DNA, and splits into two Amoebae. This is binary fission, and it happens in a fixed plane.
A Spirogyra filament breaks into short pieces. Each piece grows into a new filament. No gametes are involved.
Leishmania causes kala-azar. It has a whip-like flagellum at one end. Binary fission occurs in a definite plane in this organism.
Regeneration is mainly repair, not true reproduction. But in Planaria and Hydra it can produce new individuals.
3 · Asexual reproduction — budding, spores, vegetative propagation
Budding is a mode in which a small outgrowth, called a bud, grows on the parent and later separates. Spore formation uses a protective sac full of spores.
| Mode | How it happens | Organism |
|---|---|---|
| Budding | A bud grows on the body and detaches when mature | Yeast, Hydra |
| Spore formation | A sporangium bursts and releases spores | Rhizopus (bread mould) |
| Natural vegetative propagation | New plant grows from root, stem or leaf | Potato (eyes), Bryophyllum (leaf notches) |
| Artificial vegetative propagation | Humans cut, layer or graft plant parts | Sugarcane, rose, grapes, banana |
| Tissue culture | Tissue grown in a sterile artificial medium | Banana, sugarcane, orchids |
In Hydra, a bulge appears on the side of the body. It grows, develops tentacles, and then breaks away as a new Hydra.
Every notch on a Bryophyllum leaf can give a new plantlet. Potato “eyes” are buds that grow into new potato plants.
Vegetative propagation helps plants that produce little or no viable seed, such as banana, rose and jasmine. The new plants flower and fruit earlier.
Bud, spore, cutting, tissue — one parent, no gametes, many copies.
4 · Sexual reproduction in flowering plants
Sexual reproduction needs two gametes. A male gamete fuses with a female gamete to form a zygote.
The flower is the reproductive part of a plant. Its male part is the stamen. Its female part is the carpel, also called the pistil.
| Part | Type | Function |
|---|---|---|
| Stamen (anther + filament) | Male | Anther makes pollen grains; filament holds the anther |
| Carpel or pistil (stigma + style + ovary) | Female | Stigma receives pollen; ovary holds the ovules |
| Petal | Accessory | Attracts insects for pollination |
| Sepal | Accessory | Protects the flower bud |
A pollen grain lands on the stigma. It germinates and grows a pollen tube down the style, carrying the male gamete to the ovule.
After fertilisation, the ovary of a mango flower becomes the mango fruit. Its ovules become the seeds inside.
Pollination is only the transfer of pollen to the stigma. Fertilisation is the fusion of gametes. Do not mix the two terms.
Anther gives, stigma receives. Ovary becomes fruit, ovule becomes seed.
Stamen is not the female part. Stamen is male; carpel or pistil is female.
Wind-pollinated flowers make huge amounts of light pollen. Water-pollinated plants, like Vallisneria, release pollen into water.
5 · Sexual reproduction in human beings — the systems
In human beings, the male parent produces sperm and the female parent produces the egg. Fertilisation happens inside the female body.
| Male reproductive system | Female reproductive system |
|---|---|
| Testes make sperm and the hormone testosterone | Ovaries make the egg (ovum) and female hormones |
| Scrotum holds the testes outside the body | Oviduct, or fallopian tube, carries the egg |
| Vas deferens carries sperm away from each testis | Uterus is where the fertilised egg develops |
| Seminal vesicles and prostate gland add fluid to form semen | Cervix and vagina form the birth canal |
One sperm fuses with one egg. The zygote gets 23 chromosomes from the father and 23 from the mother, so 46 in all.
Sperm cells are very small and have a tail for swimming. The egg is much larger and does not move on its own.
Gametes have half the number of chromosomes of a body cell. In humans, body cells have 46 and gametes have 23.
Chromosomes in a body cell → in a gamete. Additional knowledge — not required for the exam.
Half from father, half from mother. That is why children resemble both parents.
The scrotum lies outside the body. Sperm formation needs a temperature a little lower than normal body temperature.
6 · Puberty, the menstrual cycle and the journey to birth
Puberty is the stage when the body becomes capable of reproduction. It starts when the testes and the ovaries begin working.
| Changes in boys | Changes in girls |
|---|---|
| Testes begin to make sperm | Ovaries begin to release eggs |
| Hair grows in armpits and pubic region; facial hair appears | Hair grows in armpits and pubic region |
| Voice deepens; Adam’s apple becomes visible | Breasts develop |
| Shoulders broaden; sweat glands become more active | Hips broaden; menstruation begins |
These changes usually begin between 10 and 14 years of age, but the exact age varies from person to person. This is completely normal.
The menstrual cycle
One ovary releases one egg about once a month. At the same time, the lining of the uterus becomes thick and spongy. It waits for a fertilised egg.
The egg is not fertilised. The thick lining is no longer needed, so it breaks down and leaves the body. This is menstruation.
The egg is fertilised. The lining is kept, and the embryo settles into it. Menstruation does not occur during this pregnancy.
From fertilisation to birth
| Stage | What happens |
|---|---|
| Fertilisation | Sperm fuses with the egg in the oviduct — a tube, not the uterus |
| Zygote | The fertilised egg divides again and again as it moves to the uterus |
| Implantation | The ball of cells settles into the thick lining of the uterus |
| Embryo and placenta | The embryo floats in fluid; the placenta passes food and oxygen from mother to baby |
| Birth | After about nine months, the uterus contracts rhythmically and the baby is born |
Fertilisation happens in the oviduct. The uterus is where the baby grows. Write the correct site in one-mark questions.
Egg plus sperm gives zygote. Zygote becomes embryo. Placenta is the lifeline.
Animals like hens and frogs lay eggs — they are oviparous. Humans and cows give birth — they are viviparous.
The placenta develops from tissues of the embryo as well as the mother. It also carries the baby’s waste away.
7 · Reproductive health — family planning, safe sex and women’s health
Reproductive health means complete physical, mental and social well-being in all matters of the reproductive system.
This section is written in the syllabus. It is assessed in the board examination. Learn the four categories of family planning clearly.
| Category | Method | How it works |
|---|---|---|
| Barrier | Condom, diaphragm | Stops the sperm from meeting the egg; also protects against infection |
| Chemical | Oral pills | Changes the hormone balance so that eggs are not released |
| IUCD | Loop, copper-T | Placed in the uterus to prevent implantation |
| Surgical | Vasectomy (male), tubectomy (female) | The vas deferens or the fallopian tube is blocked |
A barrier method is the only family planning method that also lowers the risk of sexually transmitted infections.
Surgical methods are permanent. They are chosen only when the family is complete.
Safe sex and HIV/AIDS
HIV is the virus that causes AIDS. It spreads through unprotected sexual contact, through infected blood, and from a mother to her child.
| HIV spreads by | HIV does not spread by |
|---|---|
| Unprotected sexual contact | Shaking hands or hugging |
| Transfusion of infected blood | Sharing food or water |
| Sharing needles and syringes | Coughing, sneezing or mosquito bites |
| Mother to child during pregnancy, birth or breastfeeding | Using the same toilet or swimming pool |
Prevention is written as safe sex practice, screened blood, sterile needles and public awareness. Do not add moral judgements in an answer.
Family planning: B-C-I-S — Barrier, Chemical, IUCD, Surgical.
Child bearing and women’s health
| Care needed | Why it matters |
|---|---|
| Good food and iron during pregnancy | The mother’s health decides the baby’s health |
| Regular check-ups and medical advice | Problems are found early and treated safely |
| Spacing between children | The mother’s body gets time to recover |
| Avoiding early pregnancy | A very young mother faces higher health risks |
Do not write that all family planning methods prevent infection. Only barrier methods do.
Diagram Board — figures that carry marks
These four figures appear again and again in questions. Practise the labels, not the artwork.
Draw neat outlines with a pencil. Draw label lines with a scale, and never let the label sit on the line. Two or three labels are enough for full marks.
🔑 Fact Vault
Numbers and terms that decide one-mark answers.
Important Question Bank
Questions in sequence. Tap "Show answer".
A · Multiple Choice (1 mark each)
(a) Hydra (b) Amoeba (c) Rhizopus (d) Spirogyra
Show answer
Answer: (b). Amoeba, a single-celled organism, divides into two daughter cells. Hydra buds, Rhizopus forms spores, and Spirogyra fragments.
(a) filament (b) pollen tube (c) stigma (d) sepal
Show answer
Answer: (b). The pollen grain germinates on the stigma and grows a pollen tube through the style to reach the ovule.
(a) uterus (b) ovary (c) oviduct (d) cervix
Show answer
Answer: (c). The sperm meets the egg in the oviduct. The uterus is only the site of implantation and growth.
(a) Oral pill (b) Copper-T (c) Condom (d) Tubectomy
Show answer
Answer: (c). A condom is a barrier that stops the sperm from meeting the egg. Oral pills are chemical, copper-T is an IUCD and tubectomy is surgical.
(a) 46 (b) 23 (c) 22 (d) 92
Show answer
Answer: (b). A gamete has half the number present in a body cell. Half of 46 is 23.
(a) leaf notches (b) eyes on the tuber (c) spores (d) seeds
Show answer
Answer: (b). The “eyes” on a potato tuber are buds. Each bud can grow into a new plant. Leaf notches are seen in Bryophyllum.
B · Assertion–Reason (1 mark each)
(a) Both true, R explains A. (b) Both true, R doesn’t explain A. (c) A true, R false. (d) A false, R true.
Assertion: Offspring produced by asexual reproduction are near-identical to the parent.
Reason: In asexual reproduction only one parent is involved and no gametes are formed.
Show answer
Answer: (a). Both statements are true. Because a single parent passes on its own DNA copy and no gametes fuse, the offspring closely resemble the parent.
Assertion: The lining of the uterus becomes thick and spongy every month.
Reason: It prepares to receive a fertilised egg.
Show answer
Answer: (a). Both are true and the reason explains the assertion. If the egg is not fertilised, this lining breaks down and leaves the body.
Assertion: The human embryo is connected to the mother through the placenta.
Reason: The placenta supplies nutrients and oxygen to the embryo and removes its waste.
Show answer
Answer: (a). Both statements are true and the second is the correct explanation of the first.
C · Case-Based (4 marks)
A farmer wants many banana plants that give fruit earlier than usual. In the same village, a student collects a green filamentous alga from a pond and finds that it breaks into short pieces by itself.
(i) Which method should the farmer use to grow many banana plants quickly?
(ii) Name one more plant that is commonly grown by this method.
(iii) Name the mode of reproduction seen in the alga.
(iv) State one property of the offspring produced by the alga’s method.
Show answer
(i) Vegetative propagation, specifically tissue culture. It gives many identical plants and the plants flower and fruit earlier.
(ii) Sugarcane (also rose, grapes, jasmine, orchids).
(iii) Fragmentation — the filament of Spirogyra breaks into pieces. Each piece grows into a new filament.
(iv) The offspring are near-identical to the parent, because only one parent and no gametes are involved.
D · Short & Long Answer
Show answer
1. Plants that produce little or no viable seed, such as banana, rose and jasmine, can be grown easily.
2. The new plants flower and bear fruit earlier than plants grown from seed.
3. All the new plants are near-identical to the parent, so a good variety is preserved exactly.
Show answer
1. Fertilisation: A sperm fuses with the egg in the oviduct. The fertilised egg is called the zygote.
2. Cell division: The zygote divides repeatedly and becomes a ball of cells while moving towards the uterus.
3. Implantation: The ball of cells settles into the thick lining of the uterus. This is now called an embryo.
4. Placenta: The embryo develops inside a fluid-filled sac. The placenta connects it to the mother and supplies food and oxygen. It also removes the embryo’s waste.
5. Birth: After about nine months, the uterus contracts rhythmically. The baby is pushed out through the vagina.
E · Board-Pattern Practice
Show answer
DNA copying: It passes the instructions for building the body from the parent to the offspring, so the offspring belong to the same species.
Variation is useful: It gives a population the ability to survive a change in the environment. If the surroundings change, some individuals may still survive.
Common Mistakes Table
| Mistake students make | Correct idea |
|---|---|
| Writing “binary fission in Hydra” | Hydra reproduces by budding. Binary fission is seen in Amoeba and Leishmania. |
| Using pollination and fertilisation as the same term | Pollination is the transfer of pollen to the stigma. Fertilisation is the fusion of gametes. |
| Writing that fertilisation occurs in the uterus | Fertilisation occurs in the oviduct. The uterus is where the embryo grows. |
| Saying a gamete has 46 chromosomes | A gamete has 23. The body cell has 46. |
| Calling regeneration a mode of reproduction in every organism | Regeneration is mainly repair. In Planaria and Hydra it can also produce new individuals. |
| Claiming every family planning method prevents infection | Only barrier methods reduce the risk of sexually transmitted infections. |
| Writing “the offspring are identical” in asexual reproduction | They are near-identical, because DNA copying can produce small differences. |
Active Recall & Revision
Cover the answers. Say them aloud. Then check.
Q: Name the four modes of asexual reproduction in simple organisms.
Fission, fragmentation, regeneration and budding. Spore formation and vegetative propagation are also asexual modes.
Q: Why is variation useful?
It helps a population survive when the environment changes, because some individuals may be better suited to the new conditions.
Q: Which part of the flower becomes the fruit and which becomes the seed?
The ovary becomes the fruit. The ovule becomes the seed.
Q: Where does fertilisation take place in humans, and where does the embryo grow?
Fertilisation takes place in the oviduct. The embryo grows in the uterus.
Q: What is the function of the placenta?
It passes nutrients and oxygen from the mother to the embryo, and removes the embryo’s waste products.
Q: State any two changes seen in girls at puberty.
Ovaries begin to release eggs and menstruation begins. Breasts develop, and hair grows in the armpits and pubic region.
Q: Name the four categories of family planning methods.
Barrier, chemical, IUCD and surgical methods.
Q: How does HIV not spread?
It does not spread by touching, hugging, sharing food or water, coughing, sneezing, mosquito bites or using the same toilet.
Revise after 2 days, then 3 days, then 5 days, then 7 days. This locks the memory.
Continue the Class 10 Science journey:
• Life Processes — complete notes
• Control and Coordination — complete notes
• Life Processes — 20 MCQ practice quiz
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