A seed holds a tiny baby plant inside its seed coat. The coat protects it from injury and from drying out. Some coats are thin and soft, like a bean's. Others are very hard, like a coconut's.

A seed does not sprout right away. It needs water, and it needs to be warm enough. Apple seeds will not sprout unless they have a cold spell first. A very hard coat may need to be scratched before the seed will sprout.

When water gets in, a dry seed soaks it up and swells. Then the first root comes out of the seed coat. After the root, a shoot grows up with the leaves and the stem.

Soon the plant must feed itself. Plants make their own food. This is called photosynthesis. A plant uses sunlight, water and carbon dioxide. A stem holds the leaves up so they can reach the sunlight.

Photosynthesis makes sugar for the plant. It also gives off oxygen, which people and animals breathe. Meanwhile, roots hold the plant in the ground and take in water.

Flowers are how plants make seeds. Pollination means moving pollen from the anther of a flower to the stigma. A bee drinks nectar, and pollen sticks to its body. The bee carries the pollen to the next flower.

Then seeds must travel. Some have wings or fluff, so the wind can carry them away, like maple and dandelion seeds. A coconut is a seed that floats. It can drift across the ocean and grow in a new place.

Giant sequoias are some of the biggest trees. Each one starts as a seed about the size of a grain of oatmeal. A giant sequoia can live for more than three thousand years.

Words to know

• photosynthesis: food from light
• pollen: flower dust
• stem: plant's stalk
• oxygen: gas we breathe