CBSE Class 5 Science Seed Dispersal and Its Agents Notes Set 01

Why do seeds need to travel?

A plant makes many seeds. If all of them dropped under the parent plant, they would grow in a crowd and compete for space, light, air, water and nutrients. Only the strongest seedlings would survive. To avoid this, seeds are scattered far from the parent plant. The scattering of seeds away from the parent plant is called seed dispersal. Dispersal gives young plants a better chance to get what they need to grow.

Agents of seed dispersal

Seeds are carried by four main agents: wind, water, animals and explosion of the fruit.

1. Dispersal by wind

Seeds that are light, and have wings or tufts of hair, are blown far away by the wind. Cotton, madar and dandelion seeds have hair-like tufts. The seeds of hiptage and sycamore (maple) have wings, so they spin and glide through the air.

2. Dispersal by water

Plants that grow in or near water have seeds or fruits that can float. A coconut has a spongy, fibrous outer coat that keeps it afloat, so ocean waves can carry it to a faraway shore. Once it reaches the shore, the outer coat rots and the seed is free to grow. The lotus seeds sit inside a spongy, cup-shaped fruit that floats on water. The small, light seeds of the water lily are carried by water currents.

3. Dispersal by animals

Birds and animals eat fruits, and the seeds pass out unharmed in their droppings, as happens with cherry. People also throw away seeds after eating fruit. Some seeds have hooks, spines or stiff hairs that stick to the fur of animals, the feathers of birds or our clothes. Xanthium (cocklebur), tiger-nail seed and spear grass travel in this way.

4. Dispersal by explosion

Some fruits dry up and burst open with a snap. The walls of the fruit curl as they dry and throw the seeds out with force. Castor, balsam, pea, poppy and gorse are examples.

Why dispersal matters

Dispersal also helps a plant species spread to new places. A seed that lands in a faraway field may find better soil, more sunlight or more rain than the place where its parent grows. Without dispersal a forest would not be able to spread, and new islands or clearings would stay bare. Farmers and gardeners also take advantage of this by sowing seeds apart from one another, so that every seedling has room to grow.

Quick table

1. Wind: cotton, madar, dandelion, hiptage, sycamore 2. Water: coconut, lotus, water lily 3. Animals: cherry, xanthium, spear grass 4. Explosion: castor, balsam, pea, poppy

Worked examples

Example 1. Why can a dandelion seed travel far in the wind? Answer: It is very light and has a tuft of fine hairs that works like a parachute and keeps it in the air.

Example 2. How does a coconut reach a distant seashore? Answer: Its fibrous, spongy coat helps it float, so water currents carry it over long distances until it lands on a shore.

Example 3. Why do some seeds have hooks? Answer: Hooks help them cling to the fur of animals or to clothes, so they are carried to new places.

Quick Check Questions