Double fertilisation is the process of forming a zygote and endosperm. The zygote will grow and develop into an embryo. The endosperm is the plant embryo's food source. Before double fertilisation can occur, pollination must take place. Pollination process occur when a pollen grain, produced by the stamen of a flower , lands on the carpel of another flower, on the sticky platform or stigma. A pollen grain contains sperm cells, once it lands on the stigma it develops a pollen tube. This structure will grow down the style of a carpel to its ovary. The ovary is where double fertilisation takes place.
An ovary contains at least one ovule. Inside the ovule cells divide to produce an egg and two other cells called polar nuclei. These cells are haploid, that is they have one set of chromosome designated by letter n. In addition to eggs and polar nuclei, sperm cells from a pollen grain are also haploid. Once the pollen tube reaches the micropyle, or the opening of an ovule, it releases two haploid sperm cells into the ovule. One sperm cell fuse with the egg , resulting in a diploid zygote. The other sperm cell fuse with the two polar nuclei , creating a triploid (3n) structures that will grow into an endosperm. Together, these two fertilisation events in angiosperms are called double fertilisation. After fertilisation is complete, no other sperm can enter. The fertilised ovule forms the seed, whereas the tissue of the ovary becomes the fruit , usually enveloping the seed.
Eric22 answered the question on September 30, 2018 at 16:16
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