How Do Organisms Reproduce?

Why This Chapter Matters

Reproduction is tested every year — 7-9 marks in CBSE boards. Asexual vs sexual reproduction, human reproductive system, and reproductive health are all important. Diagrams of flower parts and human reproductive organs are commonly asked.

Prerequisites

•Cell division: mitosis (Class 9 — NCERT brief mention)

•Life Processes (Chapter 6)

•Basic genetics concept helpful

Core Concepts

1. Why is Reproduction Important?

Maintains continuity of species. Without reproduction, species becomes extinct.

Reproduction is NOT essential for survival of an individual, but is essential for continuity of the species.

2. Types of Reproduction

#### Asexual Reproduction

•Single parent, no gametes (sex cells), offspring genetically identical to parent (clones)

•Faster, simpler, requires fewer resources

Types in organisms:

Type	Example	How

|---|---|---|

Binary fission	Amoeba, bacteria	Single cell divides into 2 equal halves
Multiple fission	Plasmodium (malaria parasite)	Single cell divides into many daughter cells
Budding	Yeast, Hydra	Small bud forms on parent → detaches
Fragmentation	Spirogyra (algae)	Organism breaks into pieces → each grows
Regeneration	Planaria	Cut pieces regenerate into complete organisms
Spore formation	Rhizopus (bread mould), ferns	Spores released → germinate in suitable conditions
Vegetative propagation	Potato (eyes), Bryophyllum (leaf buds)	New plant grows from vegetative part

#### Sexual Reproduction

•Two parents, gametes fuse (fertilisation), genetic variation in offspring

•More complex, produces variation (important for evolution)

3. Sexual Reproduction in Flowering Plants

Flower parts:

•Stamen (male): Filament + Anther (produces pollen grains with male gamete)

•Pistil/Carpel (female): Stigma + Style + Ovary (ovule contains female gamete/egg)

•Sepals: protect flower bud

•Petals: attract pollinators

Pollination: Transfer of pollen from anther to stigma.

•Self-pollination: Same flower or same plant

•Cross-pollination: Different plant of same species (by wind, insects, water, birds)

Fertilisation in plants:

Pollen grain lands on stigma → germinates → pollen tube grows through style → reaches ovule → pollen tube enters ovule → male gamete fuses with egg → ZYGOTE

Double fertilisation (unique to angiosperms):

One male gamete + egg → zygote → embryo

Second male gamete + 2 polar nuclei → endosperm (nutrition for embryo)

After fertilisation:

•Ovule → Seed

•Ovary → Fruit

•Zygote → Embryo

Fruit = ripened ovary | Seed = ripened ovule

4. Human Reproductive System

#### Male Reproductive System

•Testes (pair): Produce sperms (male gametes) and testosterone

- Located outside body in scrotum — sperm production needs temp slightly lower than body temp (37°C)

•Epididymis: Sperm maturation and storage

•Vas deferens: Tube carrying sperm from testes

•Seminal vesicles + Prostate gland + Cowper's gland: Produce fluids → together = semen

•Urethra: Common passage for urine and semen (not simultaneously)

•Penis: Transfers semen into female reproductive tract

#### Female Reproductive System

•Ovaries (pair): Produce eggs (female gametes/ova) and hormones (oestrogen, progesterone)

•Fallopian tubes (oviducts): Carry egg from ovary to uterus. FERTILISATION occurs here.

•Uterus (womb): Where foetus develops. Lined by endometrium.

•Cervix: Lower part of uterus

•Vagina: Birth canal, receives semen during intercourse

Menstrual cycle (28 days):

1.Menstruation (days 1-5): Uterus lining sheds (no fertilisation)

2.Follicular phase (days 1-13): Follicle develops, egg matures, oestrogen rises

3.Ovulation (day 14): Egg released from ovary

4.Luteal phase (days 15-28): Progesterone prepares uterus; if no fertilisation → cycle repeats

5. Contraception

Methods:

•Barrier methods: Condoms (also protect against STDs/STIs), diaphragm

•Chemical methods: Pills (hormonal — prevent ovulation), spermicides

•Intrauterine devices (IUDs): Copper-T placed in uterus

•Surgical methods: Vasectomy (males), tubectomy (females) — permanent

•Emergency contraception: Pills within 72 hours of unprotected intercourse

6. Sexually Transmitted Infections (STIs/STDs)

Bacterial: Gonorrhoea, syphilis (treatable with antibiotics)

Viral: HIV/AIDS, genital herpes, genital warts (no complete cure)

Prevention: Condoms provide significant (not 100%) protection. Avoid multiple partners. Regular testing.

PYQs

2023

Q: Define fertilisation. What is the site of fertilisation in humans?

Fertilisation = fusion of male gamete (sperm) and female gamete (egg/ovum) to form zygote.

In humans, fertilisation occurs in the Fallopian tube (oviduct).

2022

Q: Why are testes located outside the body cavity in humans?

Sperm production requires temperature slightly LOWER than body temperature (37°C).

Scrotum maintains 2-3°C lower temperature, essential for normal sperm production (spermatogenesis).

2021

Q: What is double fertilisation? Why is it significant?

In flowering plants, two fertilisations occur:

1.Sperm + Egg → Zygote (forms embryo)

2.Sperm + 2 polar nuclei → Primary endosperm nucleus (forms endosperm — nutrition for embryo)

Significance: Endosperm provides nutrition to developing embryo.

2020

Q: Explain vegetative propagation with two examples.

Vegetative propagation = reproduction using vegetative parts (root, stem, leaf) of a plant.

1.Potato: Eyes (axillary buds) develop into new plants.

2.Bryophyllum: Leaves have buds at margins that fall and grow into new plants.

MCQ Practice

Q1. In Amoeba, reproduction occurs by:

(A) Budding (B) Fragmentation (C) Binary fission ✓ (D) Multiple fission

Q2. Fertilisation in humans takes place in:

(A) Ovary (B) Uterus (C) Fallopian tube ✓ (D) Vagina

Q3 (Hard). Offspring of which type of reproduction would show most variation?

(A) Binary fission (B) Budding (C) Sexual reproduction ✓ (D) Vegetative propagation

[Sexual reproduction = genetic recombination = maximum variation]

Revision Notes

ASEXUAL: 1 parent, no gametes, identical offspring
Types: Binary fission, Budding, Fragmentation, Spore formation, 
       Vegetative propagation, Regeneration, Multiple fission

SEXUAL: 2 parents, gametes fuse, variation in offspring
In plants: Pollination → Fertilisation → Seed + Fruit
  Ovule → Seed | Ovary → Fruit | Zygote → Embryo

HUMAN REPRODUCTION:
  Fertilisation site: Fallopian tube
  Development site: Uterus
  Testes outside body: lower temp needed for sperm

MENSTRUAL CYCLE: 28 days
  Day 14: Ovulation (egg released)
  Days 1-5: Menstruation (if no fertilisation)

Common Mistakes:

❌ Fertilisation in humans occurs in uterus — WRONG! It occurs in Fallopian tube

❌ Pollen grain is male gamete — WRONG! Pollen grain contains the male gamete

❌ Fruit is formed from ovule — WRONG! Fruit from ovary; seed from ovule

How Do Organisms Reproduce?

How Do Organisms Reproduce?

Why This Chapter Matters

Prerequisites

Core Concepts

1. Why is Reproduction Important?

2. Types of Reproduction

3. Sexual Reproduction in Flowering Plants

4. Human Reproductive System

5. Contraception

6. Sexually Transmitted Infections (STIs/STDs)

PYQs

2023

2022

2021

2020

MCQ Practice

Revision Notes

Related Topics