Published on 09 Apr 2012 | over 5 years ago
Sexual reproduction in flowering plants.
The reproductive parts angiosperms are located in the flower. There are different parts of a flower which include sepals, petals, stamens and carpels. Stamens and carpels are the reproductive parts of a flower which contains the germ cells. The flower maybe unisexual like in the case of papaya or watermelon when it contains either stemens or carpels or bisexual as in the case of hibiscus or mustard when it contains both stamens and carpels.
Stamen is the male reproductive part and it produces pollen grains that are yellowish in color. Carpel is present in the center of a flower and is the female reproductive part. It is made of three parts. The swollen bottom part is the ovary, the middle elongated part is the style and the terminal part which maybe sticky is the stigma. The ovary contains ovules and each ovule has an egg cell. The male germ cell produced by the pollen grains fuses with the female gamete present in the ovule. This fusion of the germ cell or fertilization gives us the zygote which is capable of growing into a new plant. Thus the pollen needs to be transferred from the stamen to the stigma.
If this transfer of pollen occurs in the same flower it is referred to as self pollination. On the other hand, if the pollen is transferred from one flower to another it is known as cross pollination. This transfer of pollen from one flower to another is achieved by agents like wind, water or animals. After the pollen lands on a suitable stigma, it has to reach the female germ-cells which are in the ovary. For this, a tube grows out of the pollen grain and travels through the style to reach the ovary. After fertilization, the zygote divides several times to form an embryo within the ovule. The ovule develops into a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off. This is the reason why at times a flower part still persists in a fruit. The seed contains the future plant or the embryo which develops into a seedling under appropriate conditions. This process is known as germination.
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