Page 19 - Science Coursebook

1.6 Fertilisation

Seed formation
When the male nucleus fuses with
the female nucleus inside an ovule, it
produces a zygote.

The zygote starts to divide. It produces embryo
a little group of cells called an embryo. plant
This embryo will eventually grow into a
new plant. seed
The ovule also begins to change. It
gradually grows into a seed. zygote
ovule

How a seed is formed.

Activity 1.6
Investigating seed structure

Beans are seeds. You are going to look
carefully at the structure of a bean seed. It is
easier to do this if the bean has been soaked testa
in water for a few hours first, to soften it.

micropyle
1 Look carefully at the bean seed. Find the
structures shown on the diagram. A bean seed. scar
The testa is the tough outer coat of
the seed. The micropyle is a tiny hole
where the pollen tube grew into the cotyledons
ovule. (Remember – the seed began as an
ovule.) Bean seed with testa removed.
2 Peel the testa away from the seed. Inside,

you should find two creamy-coloured
structures. These are called cotyledons.
They contain food stores for the embryo embryo
to use when it starts to grow. plant
3 Gently pull the cotyledons apart. You will

find the embryo plant in between them. One cotyledon removed.

Summary
• When a pollen grain has landed on a stigma, it grows a tube
down to an ovule.
• The male gamete (nucleus) goes down the tube. It fuses with the
female nucleus inside an ovule, producing a zygote.
• The zygote divides over and over again, and produces an embryo plant.
• The ovule becomes a seed, with the embryo plant inside it.

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