Describe the double fertilisation in biology.

Double fertilization is a special type of sexual reproduction that happens only in flowering plants (angiosperms). It is called double fertilization because two fertilization events occur inside the embryo sac of the ovule. So, what actually happens in double fertilization?

1. The pollen tube reaches the embryo sac. After pollination, the pollen grain lands on the stigma and starts to grow a pollen tube. This tube moves down through the style and enters the ovary. Inside the pollen tube are two male gametes (sperm cells), which are carried all the way to the embryo sac.
2. Next comes the first fertilization, which leads to the formation of the zygote. One male gamete fuses with the egg cell (female gamete). This fusion forms a diploid zygote, which later develops into the embryo of the new plant.
3. Then comes the second fertilization, which leads to the formation of the endosperm. The second male gamete fuses with the two polar nuclei present in the central cell. This forms a triploid primary endosperm nucleus. It later develops into the endosperm, a tissue that stores food and nourishes the developing embryo.

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