Fertilization in seed plants is a complex process involving the fusion of male and female gametes to form a zygote, ultimately leading to the development of a seed.
Here's a breakdown of the process:
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Pollination: This is the transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower. Pollination can occur through various agents like wind, water, insects, birds, or other animals.
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Pollen Tube Growth: Once a pollen grain lands on the stigma, it germinates and develops a pollen tube. This tube grows down through the style towards the ovary, guided by chemical signals.
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Double Fertilization: This is a unique characteristic of seed plants (angiosperms). The pollen grain contains two sperm cells.
- First Fertilization: One sperm cell fuses with the egg cell inside the ovule to form a zygote (2n). This zygote will develop into the embryo, which includes the plumule (future shoot) and radicle (future root), as mentioned in the reference.
- Second Fertilization: The other sperm cell fuses with the two polar nuclei (or the secondary nucleus already formed by their fusion) in the central cell of the ovule to form the endosperm (3n). The endosperm is a nutritive tissue that provides nourishment to the developing embryo.
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Seed Development: After fertilization, the ovule develops into a seed. The zygote develops into the embryo, and the endosperm provides nutrients. The integuments (outer layers) of the ovule develop into the seed coat (testa), which protects the embryo. As the video reference indicates, the remaining contents of the ovule develop into various seed structures.
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Ovary Development: Simultaneously, the ovary (the structure surrounding the ovule) develops into a fruit, which aids in seed dispersal.
In summary, fertilization in seed plants involves pollination, pollen tube growth, double fertilization (formation of a zygote and endosperm), seed development, and ovary development into a fruit. This process ensures the continuation of the plant's life cycle.
