Fertilization in flowers occurs when a male gamete (sperm) from a pollen grain unites with a female gamete (egg cell) inside the ovule of the flower. This process leads to the formation of a zygote, which develops into an embryo within 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 Germination and Pollen Tube Growth: Once a pollen grain lands on the stigma, it germinates. It grows a pollen tube down the style (the stalk connecting the stigma to the ovary) towards the ovary. The pollen tube acts as a pathway for the male gametes to reach the ovule.
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Entry into the Ovule: The pollen tube grows through the micropyle (a small opening) of the ovule.
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Release of Male Gametes: When the pollen tube reaches an ovule, it releases two sperm cells.
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Double Fertilization: This is a unique characteristic of flowering plants (angiosperms). One sperm cell fertilizes the egg cell, forming the zygote. The other sperm cell fuses with the polar nuclei (two nuclei located in the central cell of the ovule) to form the endosperm, which provides nourishment to the developing embryo.
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Zygote and Endosperm Development: The zygote develops into the embryo of the seed. The endosperm develops into a nutrient-rich tissue that nourishes the developing embryo.
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Fruit and Seed Development: After fertilization, the ovary develops into the fruit, and the ovules develop into seeds.
In summary, fertilization in flowers involves the delivery of sperm cells from a pollen grain to the egg cell within the ovule via the pollen tube, followed by double fertilization, resulting in the formation of a zygote and endosperm, which eventually develop into the embryo and the food reserve within the seed, respectively.
