🌱 How Do Organisms Reproduce — Class 10

Asexual and sexual reproduction in plants and animals, pollination, fertilisation, contraception

1. Why Reproduce?

Reproduction is essential for the continuity of life on Earth. While not essential for the survival of an individual organism, it is critical for the survival of the species.

📖 Types of Reproduction

Asexual Reproduction: Only one parent involved. Offspring are genetically identical (clones). Faster, no need for a partner.

Sexual Reproduction: Two parents involved (male and female gametes). Offspring show variation. Slower, requires more energy.

2. Asexual Reproduction

Method	Organism	How it Works
Binary Fission	Amoeba, Bacteria, Paramecium	Cell divides into two equal halves
Budding	Yeast, Hydra	Outgrowth (bud) forms on parent, detaches
Fragmentation	Spirogyra, Planaria	Organism breaks into pieces; each regenerates
Regeneration	Planaria, Hydra, Starfish	Lost body part regenerates into complete organism
Spore formation	Rhizopus, Mucor, Moss	Spores released from sporangia; germinate when conditions are favourable
Vegetative propagation	Plants (potato, rose, grass)	New plant from part of parent (stem, leaf, root)

2.1 Vegetative Propagation in Plants

Natural: Potato (stem tuber), Ginger (rhizome), Onion (bulb), Dahlia (root tuber), Bryophyllum (leaf buds)
Artificial — Cutting: Rose, Cane — a piece of stem placed in soil, forms roots
Artificial — Grafting: Mango, Apple — join shoot (scion) of desired plant onto root (stock) of hardy plant
Artificial — Layering: Jasmine — bend stem into soil while still attached to parent plant, roots form, then separate
Artificial — Tissue culture: Orchids, Banana — grow cells from meristem in lab (allows mass production)

3. Sexual Reproduction in Flowering Plants

📖 Structure of Flower

Stamen (male) = Anther + Filament → anther produces pollen (male gametes)

Pistil/Carpel (female) = Stigma + Style + Ovary → ovary contains ovules (female gametes)

3.1 Pollination

📖 Types of Pollination

Self-pollination: Pollen from same flower or same plant falls on stigma → less variation

Cross-pollination: Pollen from different plant of same species → more genetic variation

Agents: Wind (light, dry, numerous pollen), Insects (sticky, scented pollen), Water, Birds, Bats

3.2 Fertilisation in Plants

📖 Double Fertilisation (unique to angiosperms)

1. Pollen lands on stigma → pollen tube grows through style to ovule

2. Pollen has 2 male nuclei:

• 1st nucleus + egg cell (n) → Zygote (2n) → Embryo

• 2nd nucleus + 2 polar bodies (n + n) → Endosperm (3n) — nutrition for embryo

Ovule → Seed | Ovary → Fruit

4. Sexual Reproduction in Humans

4.1 Male Reproductive System

Testes: Produce sperms (male gametes) and testosterone. Located in scrotum (cooler than body) — sperm need slightly lower temperature.
Epididymis: Sperms mature here
Vas deferens: Carries sperm to urethra
Accessory glands: Seminal vesicles, prostate, Cowper's glands — provide fluid + nutrients for sperm (together = semen)

4.2 Female Reproductive System

Ovaries: Produce eggs (ova) and hormones (oestrogen, progesterone)
Fallopian tubes: Carry eggs from ovary to uterus; fertilisation occurs here
Uterus: Where fertilised egg (zygote) implants and develops into baby
Cervix: Lower narrow part of uterus
Vagina: Birth canal; receives penis during intercourse

4.3 Menstrual Cycle

📖 28-day Cycle

Day 1–5: Menstruation (shedding of uterine lining if no fertilisation)

Day 6–13: Follicular phase — egg matures in ovary

Day 14: Ovulation — egg released from ovary

Day 15–28: Luteal phase — uterine wall thickens, prepares for implantation

If egg is fertilised → implants → pregnancy. If not → cycle repeats.

5. Contraception

Method	Type	How it works
Condom	Barrier	Prevents sperm reaching egg; also prevents STDs
Oral pills	Hormonal	Prevents ovulation (oestrogen/progesterone)
Copper-T (IUD)	Intrauterine	Prevents implantation in uterus
Vasectomy	Surgical (male)	Cuts/blocks vas deferens
Tubectomy	Surgical (female)	Cuts/blocks fallopian tubes