How do Organisms Reproduce? is Chapter 7 of CBSE Class 10 Science. Reproduction is a biological process by which organisms produce offspring of their own kind. This chapter covers both asexual and sexual reproduction in plants and animals, the human reproductive system, contraception methods, and sexually transmitted diseases.
This is one of the most important chapters for board exams — expect 8–10 marks. The human reproductive system, modes of asexual reproduction, and pollination/fertilisation in plants are the most frequently tested topics.
Key Concepts
1. Why Do Organisms Reproduce?
Reproduction is not essential for an individual organism’s survival — but it is essential for the survival of the species. Without reproduction, a species would go extinct.
Reproduction creates new individuals that are similar to but not identical to parents. This variation is important for evolution — it helps species adapt to changing environments.
At the most basic level, reproduction involves copying DNA (the genetic material). DNA in the cell nucleus carries all the information needed to build and run an organism.
Why Are There Variations?
DNA copying during reproduction is not perfectly accurate — small changes (mutations) occur. These variations may be:
- Beneficial (help survival in new conditions)
- Harmful (reduce survival chances)
- Neutral (no effect)
Over generations, beneficial variations accumulate — this is the basis of evolution.
2. Asexual Reproduction
In asexual reproduction, a single parent produces offspring without the involvement of gametes (sex cells). The offspring are genetically identical to the parent — they are clones.
Modes of Asexual Reproduction
| Mode | Description | Example |
|---|---|---|
| Fission | Parent cell divides into two (binary fission) or many (multiple fission) daughter cells | Binary: Amoeba, Leishmania; Multiple: Plasmodium (malaria parasite) |
| Fragmentation | Body breaks into fragments, each growing into a new organism | Spirogyra (filamentous alga) |
| Regeneration | Organism can regrow a complete body from a cut piece using specialised cells | Planaria (flatworm), Hydra |
| Budding | A small bud grows on the parent body, develops, and detaches as a new organism | Hydra, Yeast |
| Vegetative propagation | New plants grow from vegetative parts (roots, stems, leaves) — not seeds | Potato (tuber/eyes), Bryophyllum (leaf buds), Rose (stem cutting) |
| Spore formation | Organisms produce spores in sporangia; spores germinate into new organisms | Rhizopus (bread mould), ferns, mosses |
Note on Regeneration vs Fragmentation: Regeneration requires specialised cells that can differentiate into different cell types. Simply cutting an organism in half (fragmentation) doesn’t always lead to regeneration — only organisms with this capability (like Planaria) can regrow from fragments.
Vegetative Propagation — Important Details
| Plant | Part used |
|---|---|
| Potato | Tuber (underground stem) — eyes are buds |
| Bryophyllum | Leaf margins (buds on leaf edges) |
| Rose, Jasmine | Stem cuttings |
| Ginger, Turmeric | Rhizome (underground stem) |
| Sweet potato | Root tubers |
| Money plant | Stem cuttings in water |
Advantages of vegetative propagation:
- Plants that don’t produce seeds (banana, sugarcane, potato) can be propagated
- Genetically identical plants (preserves desirable traits)
- Faster than growing from seeds
- Plants grown are mature enough to bear flowers and fruits earlier
Tissue culture (Artificial vegetative propagation): Growing new plants from a few cells or a small tissue in a nutrient medium in a lab. Used to produce large numbers of genetically identical plants (e.g., ornamental plants, banana).
3. Sexual Reproduction
In sexual reproduction, two parents (usually male and female) contribute specialised sex cells called gametes. The male gamete fuses with the female gamete (fertilisation) to form a zygote, which develops into a new organism.
Key advantage: Sexual reproduction creates genetic variation because offspring receive DNA from two different parents. This variation is important for the survival of the species in changing environments.
4. Sexual Reproduction in Flowering Plants
Parts of a Flower
A flower is the reproductive organ of a plant. A complete flower has four whorls:
| Whorl | Part | Function |
|---|---|---|
| 1st (outermost) | Sepals (Calyx) | Protect the flower bud; usually green |
| 2nd | Petals (Corolla) | Attract insects for pollination; usually colourful |
| 3rd | Stamens (Androecium) — Male part | Produce pollen grains (contain male gametes). Each stamen has: Anther (pollen-producing) + Filament (stalk) |
| 4th (innermost) | Pistil/Carpel (Gynoecium) — Female part | Contains ovules (contain female gametes). Parts: Stigma (sticky tip) + Style (tube) + Ovary (contains ovules) |
Unisexual flowers: Have either stamens OR pistil (e.g., papaya, watermelon)
Bisexual flowers: Have both stamens AND pistil (e.g., hibiscus, mustard, rose)
Pollination
Pollination is the transfer of pollen grains from the anther to the stigma of a flower.
| Type | Description | Agent |
|---|---|---|
| Self-pollination | Pollen from anther lands on stigma of the same flower or another flower of the same plant | No external agent needed |
| Cross-pollination | Pollen from one flower lands on stigma of a flower on a different plant (of same species) | Wind, insects, water, birds, bats |
Fertilisation in Plants
- Pollen grain lands on the stigma (pollination)
- Pollen grain germinates — a pollen tube grows down through the style towards the ovary
- The male gamete travels through the pollen tube and fuses with the female gamete (egg cell) inside the ovule
- This fusion is called fertilisation — produces a zygote
- The zygote divides repeatedly to form an embryo
Post-Fertilisation Changes
| Part | Develops into |
|---|---|
| Zygote | Embryo (inside the seed) |
| Ovule | Seed (contains embryo + food store) |
| Ovary | Fruit (protects seeds, aids dispersal) |
| Petals, sepals, stamens, style | Usually fall off (wither) |
Seed Germination
When conditions are right (water, warmth, air), the seed germinates — the embryo grows into a new plant. The seed coat breaks, and the root (radicle) emerges first, followed by the shoot (plumule).
5. The Human Reproductive System
Male Reproductive System
| Organ | Function |
|---|---|
| Testes (pair, inside scrotum) | Produce sperm (male gametes) and testosterone (male sex hormone). Located outside body in scrotum because sperm need a temperature 2–3°C below body temperature. |
| Epididymis | Stores and matures sperm |
| Vas deferens | Tube that carries sperm from testis to urethra |
| Seminal vesicles and Prostate gland | Produce seminal fluid — nourishes sperm, provides medium for transport. Sperm + seminal fluid = semen |
| Urethra | Common passage for urine and semen (not at the same time) |
| Penis | Transfers semen into the female body during mating |
Testosterone: Male hormone produced by testes at puberty. Causes: voice deepening, facial hair growth, muscle development, production of sperm.
Female Reproductive System
| Organ | Function |
|---|---|
| Ovaries (pair) | Produce eggs (ova/female gametes) and oestrogen (female sex hormone). One egg is released every ~28 days (ovulation) |
| Fallopian tubes (Oviducts) | Carry egg from ovary to uterus. Fertilisation occurs here. |
| Uterus (Womb) | Thick-walled muscular organ where the embryo develops. Inner lining is richly supplied with blood vessels to nourish the embryo. |
| Cervix | Narrow opening of the uterus that connects to the vagina |
| Vagina | Receives semen; also the birth canal |
Oestrogen: Female hormone produced by ovaries at puberty. Causes: breast development, widening of hips, onset of menstruation, maturation of eggs.
Fertilisation and Development in Humans
- Sperm are deposited in the vagina during intercourse
- Sperm swim up through the uterus to the fallopian tube
- One sperm fuses with the egg in the fallopian tube → fertilisation → zygote forms
- Zygote divides repeatedly as it moves to the uterus
- The embryo implants in the thick, blood-rich lining of the uterus → implantation
- Placenta develops: a disc-shaped tissue connecting embryo to uterine wall. It provides oxygen and nutrients from mother’s blood, and removes CO₂ and waste from the embryo. Mother’s and baby’s blood do NOT mix directly.
- Pregnancy lasts about 9 months (38–40 weeks)
- Baby is delivered through the vagina (birth canal) during childbirth
Menstruation (Periods)
If the egg is NOT fertilised:
- The thick uterine lining (prepared for pregnancy) is no longer needed
- The lining breaks down and is shed — released as blood and tissue through the vagina
- This is called menstruation — lasts about 3–5 days
- The menstrual cycle repeats every ~28 days
- Menstruation begins at puberty (menarche, around age 10–15) and stops around age 45–55 (menopause)
6. Reproductive Health
Contraception (Birth Control Methods)
Methods to prevent unwanted pregnancy:
| Type | Method | How it works |
|---|---|---|
| Barrier methods | Condom (male/female), Diaphragm | Physically block sperm from reaching egg |
| Chemical methods | Oral pills (hormonal), Copper-T (IUD) | Pills: prevent ovulation; Copper-T: placed in uterus, prevents implantation |
| Surgical methods | Vasectomy (male), Tubectomy (female) | Vasectomy: vas deferens cut/blocked; Tubectomy: fallopian tubes cut/blocked |
Important: Only condoms protect against sexually transmitted diseases (STDs) — also called sexually transmitted infections (STIs). Other methods only prevent pregnancy.
Sexually Transmitted Diseases (STDs)
| Disease | Caused by | Type |
|---|---|---|
| HIV/AIDS | Human Immunodeficiency Virus | Viral |
| Gonorrhoea | Bacteria (Neisseria) | Bacterial |
| Syphilis | Bacteria (Treponema) | Bacterial |
| Genital warts | Human Papillomavirus (HPV) | Viral |
Important Definitions
| Term | Definition |
|---|---|
| Reproduction | Biological process by which organisms produce offspring of their own kind |
| Asexual reproduction | Reproduction involving a single parent without gamete fusion; offspring are clones |
| Sexual reproduction | Reproduction involving fusion of male and female gametes from two parents |
| Gamete | Sex cell (sperm in males, egg/ovum in females) — has half the number of chromosomes |
| Zygote | Cell formed by fusion of male and female gametes during fertilisation |
| Fertilisation | Fusion of male and female gametes to form a zygote |
| Pollination | Transfer of pollen grains from anther to stigma of a flower |
| Placenta | Special tissue connecting embryo to uterine wall; exchanges nutrients, oxygen, and waste |
| Menstruation | Monthly shedding of the uterine lining when no fertilisation has occurred |
| Puberty | Period when reproductive organs mature and secondary sexual characters develop |
| Ovulation | Release of a mature egg from the ovary (~once every 28 days) |
| Vegetative propagation | New plants growing from vegetative parts (roots, stems, leaves) without seeds |
| Tissue culture | Growing new plants from a few cells in a nutrient medium under sterile lab conditions |
Solved Examples (NCERT-Based)
Example 1
Why is variation beneficial to the species but not necessarily for the individual?
Answer: Variations arise during DNA copying in reproduction. For an individual, some variations may be harmful (e.g., a mutation that causes disease). However, for the species as a whole, variation is beneficial because it ensures that at least some individuals can survive if the environment changes drastically. For example, if a heat wave kills most bacteria in a population, those with a heat-resistant variation survive and reproduce — saving the species from extinction.
Example 2
Why does the uterine lining become thick and spongy before ovulation?
Answer: The uterine lining thickens and develops a rich blood supply every month in preparation for a possible pregnancy. If the egg is fertilised, the embryo needs to implant itself in this lining and receive nourishment through the blood vessels. If fertilisation doesn’t happen, this lining is no longer needed and is shed during menstruation.
Example 3
How does the embryo get nourishment inside the mother’s body?
Answer: The embryo gets nourishment through the placenta — a disc-shaped tissue embedded in the uterine wall. The placenta has finger-like projections (villi) on the embryo’s side, which are surrounded by the mother’s blood. Glucose, oxygen, and nutrients pass from the mother’s blood to the embryo’s blood through the placenta. CO₂ and other wastes pass from the embryo to the mother’s blood for removal. Importantly, the mother’s and embryo’s blood do not mix directly.
Example 4
Why is vegetative propagation practised for growing sugarcane and banana?
Answer: Sugarcane and banana do not produce viable seeds — they cannot be easily grown from seeds. Vegetative propagation (using stem cuttings for sugarcane, suckers/rhizomes for banana) is the practical method. Additionally, plants grown vegetatively are genetically identical to the parent, preserving desirable traits like sweetness, size, and disease resistance. They also mature and produce fruits faster than seed-grown plants.
Important Questions for Board Exams
1-Mark Questions
- What is the role of seminal vesicles and prostate gland?
- Name the part of the flower that develops into a fruit.
- What happens to the egg if it is not fertilised?
- Name one organism that reproduces by budding.
- Where does fertilisation occur in the human female body?
2-Mark Questions
- Differentiate between self-pollination and cross-pollination.
- Why are testes located outside the body in the scrotum?
- What is the difference between binary fission and multiple fission? Give one example of each.
- What is the function of the placenta?
- Why is DNA copying essential during reproduction?
3-Mark Questions
- Describe the process of fertilisation in flowering plants starting from pollination.
- Draw a labelled diagram of the female reproductive system and explain the function of each part.
- What is menstruation? Why does it occur? At what age does it begin and end?
- Explain three methods of contraception. Which method also protects against STDs?
- List three modes of asexual reproduction. Describe any two with diagrams.
5-Mark Questions
- Draw labelled diagrams of the male and female reproductive systems. Describe how fertilisation and development occur in humans.
- What is vegetative propagation? Explain its advantages. Describe tissue culture and its applications.
Quick Revision Points
- Reproduction ensures species survival; variations help species adapt to changing environments
- Asexual: one parent, no gametes, offspring are clones. Sexual: two parents, gamete fusion, variation
- Asexual modes: fission, fragmentation, regeneration, budding, vegetative propagation, spore formation
- Flower parts: Sepals → Petals → Stamens (male: anther + filament) → Pistil (female: stigma + style + ovary)
- Pollination → Pollen tube → Fertilisation in ovule → Zygote → Embryo (in seed); Ovary → Fruit
- Male system: Testes (sperm + testosterone) → Vas deferens → Urethra → Penis
- Female system: Ovaries (egg + oestrogen) → Fallopian tube (fertilisation here) → Uterus → Vagina
- Menstruation: ~28-day cycle; uterine lining sheds if egg is not fertilised
- Placenta: exchanges nutrients/oxygen/waste between mother and embryo (blood doesn’t mix)
- Contraception: Barrier (condom), Chemical (pills, Copper-T), Surgical (vasectomy, tubectomy)
- Only condoms protect against STDs (HIV/AIDS, gonorrhoea, syphilis)
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