Life Cycle Of A Plant

Sexual reproduction depends upon flowers. The male portions are the stamens and the female sex organs are known as stigma, which will receive pollen and ovary, in which the ova or the embryo seed grows. Wind or insects, like bees or flies, carry grains of pollen to the stigma.

Then the grain of pollen grows a pollen tube, which penetrates the ovule. The nucleus of both the pollen grain and the ovule cell fuse to produce an embryo. After the embryo grows, a food store known as the carpel is formed, along withe the endosperm and the testa or seed coat. When the seed ripens, the fruit is formed after the stamens, petals and sepals, all fall off. Either the wind or an animal carries the fruit away. If there are suitable conditions of warmth and moisture, germination of the seed occurs. First a tiny root grows. Next comes a leafy shoot. The young baby plant gets its food from the cotyledons. They also have the job of protecting the first time leaves. Enclosing the stamens and carpels are the petals, which are often brightly colored, pear nectar-producing organ and are supported by the sepals.

The cross section of the leaf, below, shows that the leaves bear cells rich in chloroplasts and are the major food producing organs. Gas flow in and out of leaf spaces through holes, the stomata, in the underside. Water enters the leaf via conducting vessels leading up from the roots. Food produced in the leaf travels around the plant via sieve tubes. Leaf veins comprise vessels, tubes and strengthening cells. The stem support the leaves and flowers, and conducts food and water between the leaves and roots. Like the leaves, it is covered in an epidermis layer that gives protection from damage and infection by bacteria, fungi and viruses, and prevents water loss. In trees, the stem is woody and covered in a protective bark.