4.6 Seed dispersal

Summary: Sometimes on a summer’s day you can see lots of things blowing in the air. Many people think this is pollen, but pollen grains are tiny and hard to see. You are probably looking at seeds being moved… Tags: science oxford-science student-book-7 biology Created: 2026-05-19 Last Updated: 2026-05-19

After this topic, you will be able to:

• describe the advantages of seed dispersal
• explain how seeds are adapted for their method of dispersal
• describe a method to investigate seed dispersal.

Think back

1. What is the name of the process of seeds starting to grow?
2. What is inside a seed?
3. How do plants take in nutrients?

Key idea Wind, animals, water, and explosion can all disperse (spread) seeds.

Key word seed dispersal

Sometimes on a summer’s day you can see lots of things blowing in the air. Many people think this is pollen, but pollen grains are tiny and hard to see. You are probably looking at seeds being moved away from the parent plant. This is called seed dispersal.

How are seeds dispersed?

Seeds are dispersed (spread) away from each other and from the parent plant. This is so they have space to grow. It is also so they do not compete for resources such as nutrients. Nearly all seeds are found inside fruits. This increases the number of ways they can be dispersed. The main methods of seed dispersal are:

• wind
• animal
• water
• explosive.

A Name four methods of seed dispersal.

Wind dispersal

The wind is very useful for dispersing seeds and fruits. To help them catch the wind, some fruits and seeds are very Light. They may also have parts that act like parachutes or wings. Examples include dandelion seeds and sycamore seeds (see Figure 1).

Figure 1Sycamore seeds are dispersed by the wind.

Working scientifically A student wants to investigate if the length of a wind-dispersed seed affects the distance it can travel. State a prediction for this investigation, including a scientific reason.

Water dispersal

Many plants that live near water, such as willow trees, produce light seeds that move on the surface of water. The seeds are transported away from the parent plant in rivers. They might germinate if they get washed up onto land. Other trees, such as coconut trees, produce woody fruits that are waterproof. They are carried away by the sea and might germinate if they reach another beach.

B Describe the structure of a seed that can be transported by water.

Animal dispersal

Animals can disperse fruits and seeds in two ways:

• Internally (inside) – animals eat fruits, including tomatoes, blackberries, and strawberries. Fruits are normally a bright colour and taste sweet. This attracts animals to them. These fruits contain seeds with hard coats. This means the seeds pass through the animal without being damaged. When they leave the animal as waste and reach the ground, the seeds might be able to germinate. They have waste material around them, which provides nutrients and helps the plant to grow.
• Externally – some seeds have hooks on them, which help them stick to animals. As an animal brushes past a plant, such as goose grass or burdock, the seeds get caught in their fur. They get carried away from the parent plant. The seeds drop off the animal’s fur and reach the ground, where they might be able to germinate. Figure 2 shows seeds adapted for external animal dispersal.

Figure 2Burdock seeds have little hooks on them to help them stick to animals’ fur.

C Name two types of seed that are dispersed by animals.

Explosive dispersal

Some fruits burst open, or explode, when they are ripe. This throws the seeds in all directions. Peapods (see Figure 3) and gorse disperse seeds in this way.

Figure 3Peapods burst open when ripe, dispersing seeds away from the parent plant.

Maths skills Three quantities that could be measured when investigating seed dispersal are the mass of the seed, the length of the seed, and the time of the flight. Give the standard units for mass, length, and time.

Stretch zone

1. Copy and complete the sentences. Seeds are blank away from the parent plant and other seeds to reduce competition. This increases their chances of having enough blank and nutrients to grow. Seeds can be dispersed by the blank, water, blank, and explosion.
2. Explain two ways that animals can disperse seeds.

Stretch zone

1. A student found a small seed that had a smooth, hard coat and a high mass. Suggest, giving reasons, the most likely method of seed dispersal for this seed.