Course Content
GROWTH AND DEVELOPMENT IN PLANTS AND ANIMALS
Biology Form 3
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Process of (Double) Fertilisation in Flowering Plants

Pollen grains land onto the stigma and adhere to it as a result of the stigma cells secreting a sticky substance.

It absorbs nutrients; and germinates forming a pollen tube; the pollen tube grows down the style to the ovary; deriving nourishment from surrounding tissue.

The pollen tube has a tube nucleus at the tip, and generative nucleus immediately behind it;

As the pollen tube grows downwards into the ovary the generative nucleus divides mitotically, to give rise to two male nuclei; which represent the male gametes; the pollen tube penetrate the ovule/embryo sac through micropyle.

 When the pollen tube enters the embryo sac, the tube nucleus breakdown/ disintegrates; leaving a clear passage for the entry of the male nuclei.

The two male nuclei then enter into the embryo sac; where one male nucleus fuses with the egg cell nucleus; to form a diploid zygote; which develop into an embryo.

The other male nuclei fuse with the two polar nuclei; to form a triploid nucleus/ primary endosperm nucleus; which later becomes the endosperm.

This (type of fertilization) is called double fertilization;

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