NCERT Solutions for Class 9th Science Chapter 11 Let us find out — Activity 11.7

Book page 217 Updated on2026-09-08

Q1.

Compare and analyse the two strategies in terms of (Table 11.3) — • Pollen to seed ratio • Efficiency of pollination and seed formation

Answer

The wind-pollinated grass makes about 6,000 pollen grains for every seed it sets; the insect-pollinated sunflower makes only about 33. Insect pollination is far more efficient per grain, but wind pollination is far cheaper per grain.

Pollination strategy	Pollen grains per flower	Seeds formed	Pollen : seed (mid-values)	Range of the ratio	Seeds per 1,00,000 grains
Wind-pollinated grasses (maize, wheat)	5,00,000 – 10,00,000	50 – 200	7,50,000 : 125 = 6,000 : 1	2,500 : 1 to 20,000 : 1	about 17
Insect-pollinated plants (sunflower)	20,000 – 40,000	800 – 1,000	30,000 : 900 = 33 : 1	20 : 1 to 50 : 1	about 3,000

best case for wind = 5,00,000 ÷ 200 = 2,500 : 1 worst case = 10,00,000 ÷ 50 = 20,000 : 1
best case for insects = 20,000 ÷ 1,000 = 20 : 1 worst case = 40,000 ÷ 800 = 50 : 1
efficiency ratio = 6,000 ÷ 33 ≈ 180

Reading the comparison:

Pollen to seed ratio. Wind pollination needs about 180 times more pollen for each seed produced. Even in the wind's best case (2,500 : 1) it is fifty times worse than the insect's worst case (50 : 1).
Efficiency of pollination. Very low for wind — most grains land on soil, water, leaves or the wrong species. High for insects, because a pollinator flies from one flower to another of the same kind.
Efficiency of seed formation. The insect-pollinated sunflower forms 800 – 1,000 seeds from a single flower head against 50 – 200 for a grass, so it converts a far larger share of its ovules into seeds.

Why the structures match the strategies: a wind-pollinated grass has small, light, smooth, dry pollen that stays airborne, and a long feathery stigma that acts like a net across the air stream. An insect-pollinated flower has large, sticky or spiny pollen that clings to a body, and a small sticky stigma that only needs to intercept what the insect brings. Each design is exactly what its delivery system requires.

Q2.

Explain why producing a very large number of pollen grains can still be an effective pollination strategy.

Answer

Because what matters to the plant is not the success rate of one grain but the number of seeds at the end — and a very small probability multiplied by a very large number still gives a useful result.

expected seeds = N × p (N = grains released, p = chance one grain reaches a stigma of its own species)
for a wheat flower: N = 7,50,000, p ≈ 1.7 × 10⁻⁴
N × p = 7,50,000 × 1.7 × 10⁻⁴ ≈ 125 seeds

The plant cannot raise p, because it cannot steer the wind. So it raises N instead. Four further reasons make this a sound bargain:

A pollen grain is a cheap thing to make. It is microscopic, dry and light. Petals, scent glands and nectar cost the plant far more per flower than a few lakh grains do — so a grass spends on pollen and a sunflower spends on advertising, and both get seeds.
No partner species is needed. Wind blows everywhere, all the time. An insect-pollinated plant fails when its pollinators disappear — exactly the apple orchard problem of exercise Question 12 — while a wind-pollinated one is never left without a carrier.
The odds are improved by how these plants grow. Wheat, maize and rice stand in dense stands of the same species, so a grain does not have to travel far to meet a stigma of its own kind. In a crowded field the effective value of p is much better than it would be for a lone plant.
The stigma is built to catch. A long, feathery stigma presents a large surface across the moving air, which raises the capture probability without the plant having to attract anything.

Why "efficient" and "effective" are not the same word here: efficiency asks how much is achieved per unit spent; effectiveness asks whether the job gets done. Wind pollination is inefficient per grain and yet completely effective, because the grains are cheap enough to be produced in the numbers the low odds demand. Wheat, maize and rice — the three crops that feed most of the world — all use it.

Was this helpful? Report an error