Seed Dispersal

Seed Dispersal PowerPoint PPT Presentation


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Types: WindAnimalSelf (Explosive) WaterThe seeds of flowering plants vary in size. Some are as small as grains of salt (e.g Foxglove), while others may be almost the size of golfballs (e.g. Horse Chestnut conkers). The difference in size reflects differences in the amount of food reserves stored in the seed for the benefit of the embryo plant inside. Usually, the larger the seed, the more food reserves it contains. This allows the germinating seed and young seedling more time to grow.9446

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Seed Dispersal

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1. Seed Dispersal * This reduces competition between the parent plant and the seeds. * It reduces overcrowding * It provides opportunities to spread the plant to new localities. * Some plants use the fruit to enable dispersal while other plants use the seed only. Can you think of three examples each of plants that use fruit dispersal and seed dispersal? * There are at least four types of seed dispersal. These are wind dispersal, animal dispersal, self- dispersal and water dispersal.

2. Types: Wind Animal Self (Explosive) Water The seeds of flowering plants vary in size. Some are as small as grains of salt (e.g Foxglove), while others may be almost the size of golfballs (e.g. Horse Chestnut conkers). The difference in size reflects differences in the amount of food reserves stored in the seed for the benefit of the embryo plant inside. Usually, the larger the seed, the more food reserves it contains. This allows the germinating seed and young seedling more time to grow. The longer a seedling has before it must become self sufficient, the greater chance it has of becoming successfully established.

3. Wind Dispersal Plants have developed a number of different adaptations either to help the seeds be released (very small light seeds) or to help the seeds stay in the air for longer. This means they can be carried greater distances. Such adaptations usually involve hairs or outgrowths which increase the surface area to catch the wind.

5. Parachute type (e.g. Ragwort on left)

6. Winged type

7. Animal Dispersal * Animals aid dispersal by either carrying the fruit or seeds on the outside of their bodies or by eating the seeds and passing them out with their droppings. * Some birds eat the fruit and then throw away the seeds. * Seeds or fruit carried on the surface of animals often have hooks to attach it to the coat of the animal. * Stickybacks and thistles are common examples.

10. Nuts such as Hazel nuts (picture at right) and acorns are also distributed by animals and birds. Jays are conspicuous in the Autumn as they collect acorns to tide them over the lean Winter. They may be responsible for the collection of several thousand acorns per bird. Not all of the acorns will be eaten, leaving some to germinate and produce new trees. Squirrels are famous for collecting nuts, not all of which will be eaten. Some will be forgotton and left to germinate later.

11. Self-Dispersal * This can involve an explosion of the fruit which then throws the seeds away from the fruit. * Examples of plants that use this mechanism are the squirting cucumber and the pea plant. * Can you find out how each of them disperses their seeds?

13. Water Dispersal * The seeds or fruits are dropped from the plant into the rivers, lakes or seas. * They, being less dense than water, float and some of them can germinateif, on being washed up on land, the conditions are favourable.

14. Plants such as Pond Iris grow in or near freshwater. The seed pods break open when they ripen. Those which fall into the water float away. The seeds may be dispersed long distances in this way. They can either germinate in the water or when they become stranded on mud.

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