Dispersal of seeds and Pollination - Class 5 Notes & Olympiad Questions

Dispersal of Seeds

Seed dispersal is the process of spreading seeds to different places. Unlike animals, plants are rooted in one spot and cannot move on their own. However, many plants need to grow in different areas to thrive.
Seed dispersal helps the young plants grow in better places that suit them well.

Agents of Seed Dispersal

There are different ways in which seeds can be dispersed.

1. Wind Dispersal

a) Seeds dispersed by wind are small and light. They may have structures like hair or wings that enable them to float through the air.
b) Examples of wind-dispersed seeds include cotton and dandelion, which have hair-like structures for wind transport.

2. Water Dispersal

a) Plants near water bodies or in water bodies use water to disperse their seeds. Seeds can float on streams, rivers, or ponds and be carried to distant places.
b) The coconut is a classic example of a seed dispersed by water, as its light and fibrous covering allows it to float easily.
c) Seeds of plants such as Water lilies and Water mints are also dispersed through water.

3. Animal Dispersal

a) Some fruits have structures like hooks, barbs, spines, or stiff hair that help them attach to animals' bodies.
b) Animals can inadvertently carry seeds when the fruits get stuck to their bodies. Examples include martynia, xanthium, Tribulus, and Pupalia.
c) Humans, animals, and birds can also disperse seeds by consuming fruits and then excreting or discarding the seeds.

4. Dispersal by Explosion

a) Some plants have pods that burst open, causing the seeds inside to scatter.
b) This happens in plants like castor, pea, mustard, lady's finger, and balsam.
c) When these fruits ripen, they explode, and the seeds are spread in different directions.

Pollination

a) Pollination is a process that helps plants make new seeds and grow more plants.
b) Inside a flower, there are different parts. One part is the male part called the stamen, and it makes something called pollen. Pollen is like a powder or tiny grains. It's usually yellow or sometimes a different colour.
c) The flower also has a female part called the pistil.
d) Pollen needs to get from the male part of one flower to the female part of another flower in order to produce seeds.
e) This process of transfer of pollens from the male parts of a flower to the female parts, enabling plants to produce seeds and create new plants in the future is known as pollination.
f) Like seeds, pollen can also be carried from one flower to another by various agents, such as insects like bees or butterflies, the wind, or even water.

Agents of Pollination

1. Insects

a) Many flowers rely on insects like bees, butterflies, and even beetles to help with pollination.
b) These insects are attracted to the bright colours and sweet nectar of flowers.
c) As they move from flower to flower, pollen sticks to their bodies and gets transferred between flowers, allowing pollination to occur.

2. Birds

a) Some colourful flowers, especially those with long tubular shapes, are pollinated by birds like hummingbirds.
b) They visit the flowers to drink nectar and unintentionally pick up and deposit pollen as they move from flower to flower.

3. Wind

a) In certain plants, like grasses and trees, wind plays a crucial role in pollination.
b) These plants produce lightweight pollen that is easily carried by the wind. The wind blows the pollen grains from one flower to another, allowing pollination to happen.

4. Water

a) Some aquatic plants, such as water lilies, use water as an agent of pollination.
b) Their pollen floats on the water's surface, and when it comes into contact with the female parts of other flowers, pollination occurs.