The Wonder of Flowering Plants
Angiosperms are plants that have the special characteristic of making flowers in order to reproduce. The flower is the reproductive organ of a flowering plant. Although you may not have thought of plants as having sexual organs, each flowering plant does contain sex cells and sexual organs.
Within each flower are male structures called stamens. The stamen consists of the anther. Which is the fuzzy part that produces pollen, and the filament, which is the stem-like structure that supports the anther. The pollen contains the sperm, or male sex cell. As in humans, each sperm contains half the normal number of chromosomes.
Flowers have female sexual organs, too. The pistil is located at the center of the flower, and it is female. It consists of a sticky stigma at the top, supported by the thick stem-like style. At the bottom of the style, near the base of the flower, is the ovary, which produces the eggs inside of the ovules. Each egg is a sex cellwith half the normal number of the plant’s chromosomes.
So what do flowering plants make the male and the female sexual organs? Babies, of course, but the baby plants begin life as seeds. Before a plant can make seeds, pollen from an anther must contact the sticky stigma of a pistil. This is called pollination.
How do plants pollinate? The stamen can’t reach over and touch the pistil. They’re close enough, though, that gravity, an insect, a gust of wind, or even a raindrop can move pollen from stamen to pistil. Some pollination occurs on the same plant, while other forms of pollination move the pollen from one plant to another.
Without the help of wind, water, insects, and other pollinators, such as nectar-sipping birds and bats, pollination would not occur as often and many flowers would fail to make seeds. And without seeds, there would be fewer plants.
When pollen does land safely on the stigma of a flower of the same species, seed-making can begin. First, a tube, called the pollen tube, will begin to growdown the style into the ovary. Next, sperm from the pollen grain will travel down the pollen tube into the ovule. Once in the ovule, the sperm will unite with the egg inside the ovule. This process is called fertilization. After fertilization occurs, the egg begins to develop into a seed starting a new generation of plants.
How does a plant use its flowers to make seeds?