What is double fertilisation? Describe the process in brief.
The type of fertilisation in plants in which one male gamete fuses with the egg to form the embryo and the other male gamete fuses with the secondary nucleus to form the primary endosperm nucleus is known as double fertilisation.
Process of double fertilisation:
After successful pollination, the pollen grain germinates on the stigma to form the pollen tube.
The pollen tube carries in the cytoplasm two male gametes and one tube nucleus into the ovary.
The pollen tube enters the ovary mostly through the micropyle region, near the egg apparatus. This movement is guided by the filiform apparatus.
Inside the ovary, the pollen tube absorbs water and bursts open, releasing the two male gametes and the tube nucleus.
The tube nucleus degenerates, and the two male gametes prepare for fusion.
One of the male gamete fuses with the egg cell to form the diploid zygote.
The other male gamete fuses with the diploid secondary nucleus to form the primary endosperm nucleus (PEN).
The zygote develops to form the new plant, while the PEN develops to form the endosperm, which provides nourishment to the developing embryo.
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