NCERT Solutions for Class 9th Science Chapter 11 .2.5 Fertilisation and seed formation — Pause and Ponder

Book page 21711 Updated on2026-09-08

Q1.

In a china-rose (hibiscus or gudhal) plant, a pollen tube grows and continues through the style after pollen lands on the stigma. Which process is about to happen next?

Answer

Fertilisation. The pollen tube is on its way to the ovule, and the moment the male gamete inside it fuses with the egg cell, fertilisation has taken place and a zygote is formed.

pollination → pollen germinates on the stigma → pollen tube grows down the style
→ tube enters the ovary and reaches an ovule
→ male gamete fuses with the egg cell = FERTILISATION
→ zygote → embryo; ovule → seed; ovary → fruit

Why a tube is needed at all: the male gamete has no tail and cannot swim, and the egg cell is locked inside an ovule at the bottom of the ovary, several millimetres below the stigma. The pollen grain solves this by growing a tube — a living extension of itself — that pushes down through the tissue of the style and delivers the gamete right to the ovule. In a plant, the male gamete does not travel; the tube carries it.

Tip: keep the two words apart. Pollination is only the transfer of pollen from anther to stigma. Fertilisation is the fusion of the two gametes. Pollination can happen without fertilisation following it — for instance if the pollen is of the wrong species and cannot grow a tube down that style.

Q2.

Look at the pictures (Fig. 11.16) of calotropis (madar) seeds and dandelion seeds given below. Can you guess what kind of seed dispersal these seeds are adapted for?

Answer

Both are adapted for dispersal by wind. Look at what Fig. 11.16 actually shows.

(a) Madar (calotropis) seeds — flat brown seeds, each carrying a dense tuft of long, fine, silky white hairs at one end.
(b) Dandelion seeds — a whole spherical white head; each seed hangs below a stalk that opens out at the top into a ring of feathery hairs, like a tiny parachute. In the picture some have already broken free and are floating away.

Why hairs make a seed travel: a falling seed speeds up until the upward drag of the air balances its weight. At that steady speed,

weight = drag → mg = ½ ρ C_d A v_t²
so v_t = √(2mg ÷ ρ C_d A) → v_t ∝ √(m / A)

The hairs add a great deal of area A while adding almost no mass m. So the terminal speed v_t drops sharply — a dandelion seed drifts down at a few centimetres per second instead of falling. Staying airborne for minutes rather than a fraction of a second, even a gentle breeze carries it hundreds of metres.

Check it yourself: drop a dandelion or madar seed with its hairs intact, and another with the hairs pinched off, from the same height. The stripped one hits the ground first every time — the mass barely changed, so the difference must come from the area.

Did you know? Dispersal matters because a seed that germinates directly under its parent competes with the parent for light, water and minerals. Wind dispersal, along with dispersal by water and by animals, is how a plant sends its offspring to ground it does not already occupy.

Q3.

A farmer plants two varieties of maize side by side, but notices that seeds form only when pollen from one variety reaches the stigma of the other. What type of pollination is this?

Answer

Cross-pollination. The pollen is moving from the anther of a flower on one plant to the stigma of a flower on a different plant of the same kind — which is the chapter's definition of cross-pollination.

Self- and cross-pollination as in Fig. 11.13. In the farmer's field the pollen must leave one variety and land on the stigma of the other, so only the right-hand route sets seed.

Why the seeds set only in this direction: the farmer's observation says that pollen landing on a stigma of the same variety produces nothing. That is a self-incompatibility — the plant recognises its own pollen and does not let it grow a tube down the style. Only pollen from a genetically different plant is accepted. Nature uses this device widely to force cross-pollination, because cross-pollination mixes the characters of two parents and so keeps producing variation.

Tip: maize is a natural cross-pollinator anyway. Its male flowers are in the tassel at the top of the plant and its female flowers are the cobs lower down, with long silky styles hanging out. Pollen shed from the tassel is carried by wind, and much of it lands on the silks of neighbouring plants — which is exactly why the farmer's two varieties, planted side by side, pollinate each other.

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