Science · Class 9 · Chapter 11

Reproduction: How Life Continues

• Vegetative propagation — New plants grow from stems, roots, or leaves — no seeds.
• Budding / Spore formation — Asexual reproduction in yeast, hydra, and fungi.
• Meiosis — Cell division that halves the chromosome number to form gametes.
• Pollination — Transfer of pollen from anther to stigma.
• Fertilisation — Fusion of male and female gametes, forming a zygote.
• External / Internal fertilisation — Gametes meet outside / inside the female's body.
• Ovulation — Release of a mature egg from the ovary.
• Menstruation — Monthly shedding of the uterine lining, if no fertilisation occurs.

Chapter 11 · Concept 1 of 20

Two Modes of Reproduction

• Asexual — One parent produces offspring that are near-exact genetic copies of itself — seen in bacteria, yeast, hydra, and many plants.
• Sexual — Two parents each contribute genetic material — offspring inherit a mix of traits, creating variation between generations.

Chapter 11 · Concept 2 of 20

Vegetative Propagation in Plants

• New plants sprout directly from a parent's stem, root, or leaf — no seeds involved, and only one parent.
• Everyday examples — Potato and ginger sprout from fleshy underground stems; sugarcane and money plant grow from stem cuttings; Bryophyllum leaves sprout tiny plantlets along their edges.

Chapter 11 · Concept 3 of 20

Cutting, Grafting, Layering, and Tissue Culture

• Method | How it works
• Cutting — A stem piece is planted directly in soil, and grows roots of its own
• Grafting — A stem piece from one plant is fitted into a cut/slit on a rooted plant of another variety
• Layering — A twig is bent and buried while still attached to the parent; once it roots, it's cut free
• Tissue culture — Shoot-tip cells are grown on nutrient media to mass-produce healthy, virus-free plantlets

Chapter 11 · Concept 4 of 20

Budding and Spore Formation

• Budding — In yeast and hydra, a small outgrowth (bud) forms on the parent, enlarges, and eventually separates to live independently.
• Spore formation — Fungi (like the mould on bread) release millions of lightweight spores into the air, which germinate into new individuals wherever moisture and nutrients allow.

Chapter 11 · Concept 5 of 20

Mitosis: The Basis of Asexual Reproduction

• Every method in this section — vegetative propagation, budding, spore formation — relies on the same cell-division process underneath.
• Mitosis produces identical daughter cells — Since offspring arise from a single parent through mitosis, they carry the exact same chromosome number and genetic makeup — they are clones of the parent.

Chapter 11 · Concept 6 of 20

Sexual Reproduction Needs Meiosis

• If every generation inherited a full chromosome set from both parents, the number would double each time. Meiosis solves this.
• Diploid → haploid gametes — Meiosis halves the chromosome number, forming gametes (sperm and egg in animals; pollen and ovule in plants) — so when two gametes fuse, the normal number is restored.

Chapter 11 · Concept 7 of 20

Meiosis Creates Genetic Variation

• As chromosome pairs separate during meiosis, each gamete randomly receives one chromosome from each pair.
• Millions of possible combinations — With just 3 pairs of traits, 8 combinations are possible. With 23 human chromosome pairs, the number of possible combinations is enormous — making each person genetically unique, even among siblings.

Chapter 11 · Concept 8 of 20

Structure of a Flower

• Part | Role
• Sepal — Protects the flower while it's still a bud
• Petal — Attracts pollinators with colour and fragrance
• Stamen (male) — Filament + anther — produces pollen grains (male gametes)
• Pistil (female) — Stigma + style + ovary — the ovary holds ovules with the egg cell

Chapter 11 · Concept 9 of 20

Self-Pollination, Cross-Pollination, and Pollinators

• Self vs. cross — Self-pollination: pollen moves to the stigma of the same or another flower on the same plant. Cross-pollination: pollen travels to a flower on a different plant of the same species.
• Agents of pollination — Wind (wheat, maize), water (Vallisneria, Hydrilla), insects (sunflower, hibiscus), or birds (coral tree) — each shapes the flower's colour, scent, and pollen.

Chapter 11 · Concept 10 of 20

Fertilisation and Seed Formation

• A pollen tube grows from the stigma, down through the style, to the ovule — carrying the male gamete to fuse with the egg cell.
• Zygote → embryo, ovule → seed, ovary → fruit — This fusion of gametes is fertilisation. The fertilised egg (zygote) develops into an embryo, the ovule becomes the seed, and the ovary swells into the fruit around it.

Chapter 11 · Concept 11 of 20

Two Pollination Strategies Compared

• Strategy | Pollen released per flower | Average seeds formed
• Wind-pollinated (maize, wheat) — 5,00,000 – 10,00,000 — 50 – 200
• Insect-pollinated (sunflower) — 20,000 – 40,000 — 800 – 1,000

Chapter 11 · Concept 12 of 20

External and Internal Fertilisation in Animals

• External fertilisation — Eggs and sperm are released into water (frogs, most fish). Many eggs are laid, but survival is low — currents and predators destroy most of them.
• Internal fertilisation — Occurs inside the female's body (reptiles, birds, mammals). Fewer eggs are produced, but the embryo is better protected, so survival is generally higher.

Chapter 11 · Concept 13 of 20

Reproductive Strategies Across Animals

• Animal | Fertilisation | Eggs produced | Survival of young
• Fish — External — 100s – 1000s at a time — Low
• Frog — External — 5,000 – 50,000 at a time — Low
• Lizard — Internal — 2 – 20 at a time — Moderate
• Bird — Internal — 1 – 15 at a time — Moderate to High

Chapter 11 · Concept 14 of 20

The Male Reproductive System

• Organ | Function
• Testes (in the scrotum) — Produce sperm and male hormones; kept cooler than body temperature
• Vas deferens — Carries sperm from the testes to the urethra
• Seminal vesicles & prostate gland — Add fluid that nourishes sperm and helps them move
• Urethra — Common passage for sperm and urine, through the penis

Chapter 11 · Concept 15 of 20

The Female Reproductive System

• Organ | Function
• Ovaries — Produce eggs (female gametes) and hormones
• Oviducts (fallopian tubes) — Connect each ovary to the uterus; where fertilisation occurs
• Uterus — The bag-like organ where a fertilised egg implants and a foetus develops
• Cervix & vagina — Narrow passage connecting the uterus to the outside of the body

Chapter 11 · Concept 16 of 20

Gametogenesis: Sperm vs. Egg

• Feature | Sperm | Egg
• Size — Very small — Large
• Number produced — Millions — Few (one per month, from puberty)
• Stored nutrients — Absent — Present
• Motility — Actively motile — Non-motile

Chapter 11 · Concept 17 of 20

What Happens When a Sperm Meets an Egg

• After ovulation, a released egg travels into the oviduct. Sperm entering the reproductive tract swim to meet it.
• Fusion, division, implantation — If a sperm fuses with the egg, a zygote forms. It divides repeatedly while travelling to the uterus, then implants into the thickened uterine lining — marking the start of pregnancy.

Chapter 11 · Concept 18 of 20

The Menstrual Cycle

• Days | What happens
• 1 – 5 — Menstruation: the thickened uterine lining sheds, if no fertilisation occurred
• 6 – 14 — The uterine lining gradually rebuilds; an egg matures in the ovary
• ~14 — Ovulation: the ovary releases a mature egg
• 15 – 28 — The lining thickens further, rich with blood vessels; if unfertilised, it breaks down and the cycle repeats

Chapter 11 · Concept 19 of 20

Pregnancy and Childbirth

• Trimester | What happens
• First — The embryo forms and major organs begin developing; called a foetus from about week 9
• Second — The foetus grows bigger and stronger; movements usually become noticeable
• Third — Rapid growth as the baby prepares for life outside the womb

Chapter 11 · Concept 20 of 20

Sexual Maturity, STIs, and Contraception

• Physical maturity ≠ emotional readiness — The body becomes capable of reproduction gradually during adolescence, but emotional and social maturity — making thoughtful, responsible decisions — takes longer to develop.
• Preventing infection and unwanted pregnancy — Condoms are a barrier method that reduces the spread of Sexually Transmitted Infections (STIs) and also prevents pregnancy. Other methods include contraceptive pills and IUDs (like Copper-T).

Quick Recap

Check Your Understanding

1. 1Arrange the stages of sexual reproduction in plants in the correct order: (i) Pollen germination on stigma (ii) Fertilisation (iii) Pollination (iv) Formation of zygote
2. 2Assertion (A): The zygote formed after fertilisation immediately attaches to the uterus wall. Reason (R): The uterus wall is always prepared to receive the zygote. Choose the correct option.
3. 3Why does asexual reproduction produce offspring that are genetically identical to the parent?