Reproduction — Class 10 Biological Science
"Every living thing reproduces. It is the ONLY life process not essential for the SURVIVAL of the individual — but it is essential for the SURVIVAL of the SPECIES."
1. Asexual Reproduction (One Parent)
Offspring are genetically IDENTICAL to the parent (CLONES). No gametes involved. No fertilisation. Common in simpler organisms and plants.
| Method | How It Works | Example |
|---|---|---|
| Binary Fission | Parent cell divides into TWO identical daughter cells. | Amoeba. Bacteria. |
| Multiple Fission | Parent divides into MANY daughter cells simultaneously. | Plasmodium (malaria parasite). |
| Budding | Small OUTGROWTH (bud) forms. Grows. Detaches. | Yeast. Hydra. |
| Fragmentation | Body breaks into FRAGMENTS. Each fragment → new organism. | Spirogyra (algae). |
| Regeneration | Lost body part REGROWS. In some organisms: whole body from a fragment. | Planaria (flatworm). Hydra. Starfish. |
| Vegetative Propagation | New plant from VEGETATIVE parts (stem, root, leaf). | Stem cutting (rose, sugarcane). Tuber (potato — 'eyes'). Leaf (Bryophyllum — plantlets on leaf margins). Rhizome (ginger). Bulb (onion). |
Tissue Culture (Modern Method)
Growing whole plants from a SMALL PIECE of plant tissue on a NUTRIENT MEDIUM under STERILE conditions. 'Thousands of identical plants from a single parent. Used for: commercial propagation of orchids, bananas, disease-free plants.'
2. Sexual Reproduction in Flowering Plants
The Flower — Reproductive Structure
STAMEN (Male) : ANTHER produces POLLEN GRAINS (contain male gametes). FILAMENT stalk. PISTIL/CARPEL (Female) : STIGMA — sticky tip, receives pollen. STYLE — connects stigma to ovary. OVARY — contains OVULES (each ovule contains an EGG CELL).
Pollination — Transfer of Pollen to Stigma
| Self-Pollination | Cross-Pollination | |
|---|---|---|
| Definition | Pollen from SAME flower or SAME plant | Pollen from DIFFERENT plant of same species |
| Agents | Not needed | Wind. Insects. Birds. Water. Bats. |
| Genetic variation | LOW | HIGH (stronger offspring) |
| Examples | Pea. Wheat. Rice. | Most flowering plants. |
Double Fertilisation (UNIQUE to Angiosperms)
Pollen grain germinates on stigma → pollen tube grows through style → enters ovule through micropyle. TWO male gametes are released:
- First male gamete + Egg cell → ZYGOTE (2n) → develops into EMBRYO.
- Second male gamete + 2 Polar nuclei → ENDOSPERM (3n) → nourishes the developing embryo. 'TWO fusion events. This is DOUBLE FERTILISATION. It occurs ONLY in flowering plants.'
Post-Fertilisation
Ovary → FRUIT (protects seeds, aids dispersal). Ovules → SEEDS. Seed contains: EMBRYO (baby plant — with RADICLE → root, PLUMULE → shoot). COTYLEDONS (food storage — monocots have 1, dicots have 2). SEED COAT (protective).
3. Human Reproduction
Male Reproductive System
Testes (in scrotum — 2-3°C COOLER than body temperature — essential for sperm production). Produce SPERM (male gametes — 23 chromosomes, haploid). Produce TESTOSTERONE. Vas deferens (sperm duct). Urethra (common passage for urine and semen).
Female Reproductive System
Ovaries (2): Produce EGGS (ova — female gametes — 23 chromosomes, haploid). Produce OESTROGEN and PROGESTERONE. Fallopian Tubes (Oviducts): Site of FERTILISATION. Uterus (Womb): IMPLANTATION of embryo. Development of foetus. Cervix. Vagina.
Fertilisation
Sperm + Egg → ZYGOTE (46 chromosomes — diploid — 23 from each parent). Occurs in FALLOPIAN TUBE. Zygote divides repeatedly (CLEAVAGE) as it travels to uterus.
Implantation and Development
Blastocyst embeds in UTERINE WALL (endometrium). PLACENTA forms: connection between mother and embryo. Provides O₂ and nutrients. Removes waste (CO₂, urea). Produces hormones (progesterone — maintains pregnancy). 'The placenta is a TEMPORARY ORGAN. It is the LIFELINE between mother and baby. The mother's blood and the foetus's blood are SEPARATE — they exchange substances through the placental membrane.'
Menstrual Cycle (~28 days)
Follicular Phase (Day 1-14): Egg matures in ovary. Oestrogen rises. Endometrium thickens. Ovulation (Day 14): Egg released. Luteal Phase (Day 15-28): Corpus luteum produces progesterone. If no fertilisation → progesterone drops → endometrium sheds → MENSTRUATION.
Reproductive Health
Contraception methods: Barrier (condom — also protects against STIs). Hormonal (oral pills). IUD (Copper-T). Surgical (vasectomy — male. tubectomy — female). 'Access to reproductive healthcare is a FUNDAMENTAL RIGHT. Informed choice saves lives.'
4. Common Mistakes
- 'Pollination = fertilisation' — Pollination is pollen reaching STIGMA. Fertilisation is fusion of gametes in the OVULE. Pollination comes FIRST.
- 'Double fertilisation = two zygotes' — ONE zygote + ONE endosperm (3n). NOT two embryos.
- 'Placenta mixes mother's and baby's blood' — They are SEPARATE. Exchange occurs through a MEMBRANE.
- 'Asexual reproduction produces variation' — Asexual produces CLONES (identical). Sexual produces VARIATION.
5. AP SSC Exam Focus
| Topic | Marks |
|---|---|
| Asexual reproduction types | 3-4 |
| Double fertilisation | 3-4 |
| Human reproductive system (diagram) | 4-5 |
| Menstrual cycle | 2-3 |
| Reproductive health | 2-3 |
6. Asexual Reproduction — Detailed Types
Binary Fission — 'Splitting into Two'
The parent cell divides into TWO IDENTICAL daughter cells. In Amoeba: nucleus divides FIRST (mitosis) → cytoplasm divides → two Amoebae. In Bacteria: DNA replicates → cell wall grows inward → divides. 'Binary fission is SIMPLE and FAST. A bacterium can divide every 20 minutes — one bacterium can become MILLIONS in a few hours!'
Multiple Fission — 'Splitting into Many'
The parent cell divides into MANY daughter cells SIMULTANEOUSLY. In Plasmodium (malaria parasite) : The nucleus divides MANY times → cytoplasm surrounds each nucleus → cell membrane forms → MANY daughter cells are released at once. 'When conditions are unfavourable, the parent forms a CYST (protective wall). Inside the cyst, multiple fission occurs. When conditions improve, the cyst bursts → releases many organisms.'
Budding — 'Growing a New Individual'
A small OUTGROWTH (bud) forms on the parent body. The bud GROWS. The nucleus divides → one nucleus moves into the bud. The bud DETACHES → becomes an INDEPENDENT organism. In Yeast: Microscopic budding — visible under a microscope. In Hydra: A small TUBE-LIKE bud grows → develops tentacles and a mouth → detaches. 'The bud is genetically IDENTICAL to the parent. It is a CLONE.'
Fragmentation — 'Breaking into Pieces'
The body of the organism breaks into TWO or MORE fragments. EACH fragment → a COMPLETE new organism. In Spirogyra (a green alga) : The filament breaks into pieces → each piece grows into a NEW filament. 'Fragmentation happens ONLY in SIMPLE organisms. Complex organisms CANNOT reproduce this way — you cannot grow a new human from a severed finger!'
Regeneration — 'Healing and Rebuilding'
Regeneration is the ability to REGROW lost body parts. In some organisms, an ENTIRE NEW INDIVIDUAL can grow from a SMALL FRAGMENT. In Planaria (flatworm) : If cut into pieces, EACH piece can grow into a COMPLETE new worm. In Hydra: Can regenerate a new individual from a small fragment. In Starfish: A lost arm can grow back — and in some species, a severed arm with part of the central disc can grow a NEW starfish.
'Regeneration occurs through SPECIALISED cells that DIVIDE RAPIDLY and DIFFERENTIATE into various cell types. In higher animals (including humans), regeneration is LIMITED — we can heal wounds and regrow skin and liver tissue, but we cannot regrow limbs.'
Vegetative Propagation — 'Natural Cloning in Plants'
New plants grow from VEGETATIVE PARTS (stem, root, leaf) — NOT from seeds. Offspring are CLONES of the parent.
| Plant Part | Example | How It Works |
|---|---|---|
| Stem (runner) | Strawberry | Horizontal stems (runners) grow along ground → roots form at nodes → new plants |
| Stem (tuber) | Potato | 'Eyes' (buds) on the tuber → each eye can grow into a new plant |
| Stem (rhizome) | Ginger, Turmeric | Underground horizontal stems → nodes produce new shoots and roots |
| Stem (bulb) | Onion, Garlic | Fleshy leaves surround a bud → new plant from the bud |
| Stem (corm) | Colocasia (Arbi) | Short, thick underground stem → stores food → new plant from buds |
| Root | Sweet potato, Dahlia | Adventitious buds on roots → new shoots grow from stored food |
| Leaf | Bryophyllum (Sprout leaf plant) | Plantlets develop along the leaf MARGINS → fall → root → new plants |
| Leaf | Begonia | Leaf placed on soil → roots form at cut veins → new plants |
'Farmers use vegetative propagation because: (1) It is FASTER than growing from seed. (2) The offspring are GENETICALLY IDENTICAL to the parent — the desired traits are PRESERVED. (3) Seedless varieties can be propagated (banana, grapes).'
7. Sexual Reproduction in Plants — Detailed
Structure of a Flower
Pedicel: The stalk that attaches the flower to the stem. Thalamus (Receptacle): The thickened part at the base that holds the floral parts. Calyx: Outermost whorl of SEPALS. Usually green. PROTECTS the flower in bud stage. Corolla: Second whorl of PETALS. Often COLOURED and FRAGRANT — attracts POLLINATORS (insects, birds). Androecium (Male whorl): STAMENS — each stamen has a FILAMENT (stalk) and an ANTHER (produces POLLEN GRAINS). Gynoecium (Female whorl): PISTIL/CARPEL — has STIGMA (sticky tip, receives pollen), STYLE (tube connecting stigma to ovary), OVARY (contains OVULES — each ovule has an EGG CELL).
Pollination — Types and Agents
| Pollination Type | Definition | Percentage of Flowering Plants |
|---|---|---|
| Self-Pollination | Pollen from SAME flower (or same plant) reaches stigma | ~10% |
| Cross-Pollination | Pollen from DIFFERENT plant reaches stigma | ~90% |
Agents of Cross-Pollination: Wind (Anemophilous): Light, dry pollen. Large, feathery stigmas. Example: grasses, wheat, maize, rice. 'Wind-pollinated flowers are usually SMALL, NOT colourful, and produce LARGE amounts of pollen (which is why some people get hay fever).' Insects (Entomophilous): Brightly coloured petals. Fragrant. Nectar. Sticky pollen. Example: rose, sunflower, mustard. Birds (Ornithophilous): Bright red/orange flowers. Abundant nectar. Example: bottlebrush, hibiscus. Water (Hydrophilous): Pollen is released on the water surface. Example: Vallisneria, Hydrilla.
'Cross-pollination is ADVANTAGEOUS because it produces GENETIC VARIATION — offspring have new combinations of traits. Self-pollination is a BACKUP mechanism — it ensures reproduction even when no pollinators are available.'
Fertilisation — The Fusion of Gametes
- Pollen grain LANDS on the stigma.
- The pollen grain GERMINATES → a POLLEN TUBE grows down through the style.
- The pollen tube enters the ovule through a tiny opening called the MICROPYLE.
- TWO male gametes are released into the embryo sac.
Double Fertilisation — Unique to Angiosperms
First Fusion: Male gamete (n) + Egg cell (n) → ZYGOTE (2n) → develops into EMBRYO (the baby plant). Second Fusion: Male gamete (n) + 2 POLAR NUCLEI (n+n = 2n) → ENDOSPERM (3n, triploid) → nutritive tissue for the embryo.
'Double fertilisation is FOUND ONLY IN FLOWERING PLANTS (angiosperms). It is their UNIQUE FEATURE. The endosperm develops ONLY if fertilisation occurs — this saves the plant's energy.'
Seed and Fruit Formation
- After fertilisation: OVARY → matures into FRUIT. OVULES → mature into SEEDS.
- The fruit PROTECTS the seeds and aids in DISPERSAL (by wind, water, animals, explosion).
- The seed contains: TESTA (seed coat — protective), COTYLEDONS (food storage — 1 in monocots, 2 in dicots), RADICLE (embryonic root), PLUMULE (embryonic shoot).
8. Reproductive Health — Extended
Sexually Transmitted Infections (STIs)
| Disease | Caused By | Symptoms | Treatment |
|---|---|---|---|
| Gonorrhoea | Bacteria (Neisseria) | Painful urination, discharge | Antibiotics (curable) |
| Syphilis | Bacteria (Treponema) | Sores, rash, organ damage | Antibiotics (curable) |
| HIV/AIDS | Virus | Weakens immune system → opportunistic infections | Antiretroviral therapy (NOT curable — manageable) |
| Genital Warts | Virus (HPV) | Warts on genitals | Some types cause CERVICAL CANCER (vaccine available) |
Prevention: Use CONDOMS (barrier method — only method that protects against STIs). Get TESTED. Be in a MUTUALLY FAITHFUL relationship.
Contraception — Family Planning Methods
Natural: Rhythm method (avoid fertile period). Withdrawal. 'UNRELIABLE — not recommended for those who want certainty.' Barrier: Condoms (male and female). Diaphragm. Cervical cap. 'Condoms have the ADDED BENEFIT of STI protection.' Hormonal: Oral contraceptive pills (oestrogen + progesterone → suppress ovulation). Emergency contraceptive pill ('morning-after pill' — NOT for regular use). Patches. Injections. Intrauterine Devices (IUDs) : Copper-T (creates inflammation → prevents implantation). Hormonal IUD. 'Highly effective. Can be left in place for 5-10 years.' Surgical: Vasectomy (male — vas deferens cut and tied). Tubectomy (female — fallopian tubes cut and tied). 'PERMANENT. Should only be chosen if no more children are desired.' Abortion: Medical termination of pregnancy (MTP). Legal in India up to 24 weeks (under certain conditions). Safe when performed by trained medical professionals.
9. Common Mistakes (Additional)
- 'Fragmentation and regeneration are the same' — In FRAGMENTATION, the organism BREAKS into pieces, and each piece grows into a NEW organism. In REGENERATION, the organism HEALS by replacing lost parts — the original organism survives.
- 'All plants grow from seeds' — MANY plants (potato, ginger, sugarcane, rose) are grown from vegetative parts, not seeds.
- 'HIV spreads through casual contact' — HIV spreads ONLY through: unprotected sexual contact, infected blood (needle sharing, transfusion), mother to child (pregnancy, childbirth, breastfeeding). NOT through handshakes, sharing food, coughing, or mosquito bites.
10. Self-Test Questions
- Tabulate FIVE types of asexual reproduction with examples.
- Differentiate between SELF-POLLINATION and CROSS-POLLINATION.
- Explain DOUBLE FERTILISATION in angiosperms. Why is it unique?
- Draw a labelled diagram of the HUMAN FEMALE REPRODUCTIVE SYSTEM.
- Describe the MENSTRUAL CYCLE. What happens when fertilisation does NOT occur?
- What are the functions of the PLACENTA?
- Name THREE methods of contraception and explain how each works.
- Differentiate between FRAGMENTATION and REGENERATION with examples.
- Explain the role of VEGETATIVE PROPAGATION in agriculture.
- What is the importance of the ENDOSPERM in seeds?
Answers to Selected Questions: Q7: (1) Condom — barrier prevents sperm from reaching egg. (2) Oral pills — hormones suppress ovulation. (3) Copper-T — IUD prevents implantation. Q10: Endosperm provides NUTRITION to the developing embryo. In monocots (like rice, wheat, maize), the endosperm persists and forms the main food storage — which is why grains are a staple food for humans.
