Do One Thing

Autumn Term 2008

The Do One thing this term is called feeding wildlife. This page takes the topic further and looks at the why plants produce seeds and fruits, and the ways in which seeds and fruits can be dispersed. Read on for...

• What are seeds and fruits?
• How are seeds and fruits dispersed?
• Seed and fruit dispersal fact file
• Lesson ideas for teachers

What are seeds and fruits?

Seeds are formed in the female part of the flower after the ovule has been fertilised by pollen.

A pollen grain lands on the stigma when the flower is pollinated (e.g. by a bee). A tube grows down through the style to the ovary and into the ovule (known as the pollen tube). When the male pollen and female ovule join, the ovule is fertilised. The fertilised ovule develops into a seed. This seed may eventually grow into a new plant.

The ovary protects the seed as it develops. The combination of fertilised ovule and ovary is called the fruit. In scientific terms, the word 'fruit' has a slightly different meaning to its everyday usage. As well as familiar edible fruits (like apples, bananas and lemons) acorns, holly berries and sycamore 'helicopters' are all classed as fruits.

Plants need to spread (or disperse) their seeds some distance from the parent plant, so that the new plant is not in competition (for light, water and mineral salts).

Not all seeds land in a suitable place to grow. Some seeds do not even germinate, while others will die young, before the new plant is able to make seeds of its own. To overcome this problem, plants usually produce large numbers of seeds to make sure that some survive.

How are seeds and fruits dispersed?

Seeds and fruits are dispersed in four main ways.

• by animals
• by the wind
• self dispersal
• by water (not so important in the British Isles)

The flow chart below shows examples of common wild plants, and the many different ways in which these plants disperse their fruits and seeds. Click on the pictures to find out more about each.

Seed and fruit dispersal fact file

Find out more about how seeds and fruits are dispersed

	Blackberries Juicy fruits dispersed by animals Each blackberry is made up of many separate sections, each containing a single seed They are collected and eaten by many animals, including humans The juicy part of the fruit is digested, but the hard seeds pass through into the animal's droppings
	Holly Juicy fruits dispersed by animals Each holly berry contains a single seed The berries are mainly dispersed by birds Since birds can see colour well, holly berries are coloured red so that they contrast with the glossy green leaves
	Acorns Takeaways dispersed by animals Acorns are the fruit of the oak tree. Each acorn contains a single large seed Acorns are collected and stored for winter food by small mammals such as squirrels and mice. Many mammals do not see well in colour, so seeds do not need to be brightly coloured to attract them
	Horse chestnut Takeaways dispersed by animals The fruit of the horse chestnut is actually the prickly green case This splits to reveal the seed of the horse chestnut tree - the conker Ripe conkers are carried away from the parent tree by small mammals and used for winter food
	Cleavers Hitch-hikers dispersed by animals Cleavers is a spreading plant which has 'sticky buds' - small round fruit with hooked bristles which cling to the fur of passing animals The stems and leaves also have these bristles, so animals may pick up long trailing bits of stem with many fruits
	Sycamore Winged fruits dispersed by the wind Sycamore fruit are arranged in pairs, each with an off-centre wing After the two wings have separated, the fruit spins as it falls, carrying it further from the parent tree
	Dandelion Parachutes dispersed by the wind The seed head of the dandelion is made up of many individual 'parachutes', each attached to a single fruit and seed The 'parachute' keeps the seed in the air, allowing it to be carried away on the breeze from the parent plant
	Poppy Self dispersed - pepperpot-shaped fruit The fruit of the poppy is shaped like a 'pepperpot', with a ring of holes near the top It is arranged at the top of a stiff but springy stem When an animal walks past, or the plant is blown by the wind, the stem is bent back, releasing the small black seeds through the ring of holes
	Himalayan balsam Self dispersed - exploding fruit As the fruit ripens, pressure builds up inside the fruit as the cells swell When a passing animal brushes against the plant, the ripe fruit splits open explosively, and scatters the seeds widely

Illustrations by Dr Anne Bebbington

FURTHER LESSON IDEAS FOR TEACHERS:

1. The sultana game

The sultana game is an excellent introductory activity to the concept of fruit and seed dispersal by animals. At the start of the lesson, each pupil is given a sultana, and asked to pretend to be a squirrel creating a winter food store. At the end of the lesson, the pupils are asked to retrieve their sultanas. Several pupils may have forgotten where they put their winter food stores! For more detailed guidance for teachers visit the Science and Plants for Schools (SAPS) website.

2. Constructing a key to fruit dispersal mechanisms

This activity allows pupils to extend the key to fruit dispersal mechanisms given above. Pupils identify the dispersal mechanisms used by plants in the school grounds or local area, and use these to compile a simple key. For more detailed guidance for teachers visit the Science and Plants for Schools (SAPS) website. You can also download a Pupil Worksheet (pdf, 80kb) for pupils to use when looking at fruit dispersal outside.

3. Plant Science Image Database

The SAPS Plant Science Image Database is a source of additional colour photographs of fruits and seeds. It includes a series ('From flower to fruit') which illustrates the development of fruits after fertilisation.

Interested in taking part in a Europe-wide fieldwork survey? Find out more about the BEAGLE project (pdf, 280kB).