In this topic you will learn about how plants behave.

A stimulus is something in the environment (such as light or heat) that causes living things to react. A response is what a living thing does as a result of a stimulus. Plants respond to a stimulus, but they tend to do it more slowly than animals do. A tropism is a growth response of a plant to slowly bend or curve toward or away from a stimulus. Tropisms help a plant survive in its environment.

There are several major kinds of tropisms. A plant responding to the stimulus of gravity by sending its roots downward into the soil is called gravitropism. Stems show negative gravitropism. They grow away from the force of gravity by growing into the air where their leaves can get the most sunlight.

Light is very important to the survival of a plant. Plants respond to changes in light. These responses are called phototropisms. If a plant is exposed to light coming from only one direction, its stem will bend in that direction. This is called positive phototropism.

Hydrotropism is when the roots of a tree grow toward a source of water. Some plants, like squash or grapevines, show a response to touch. The vines send out threadlike tendrils that coil around whatever they touch.

Plants survive in deserts, rain forests, and the Arctic because they have adapted to the environment. An adaptation is a characteristic that enables a living thing to survive in its environment. Plants that bloom in late spring or early summer when there is more daylight than darkness are called long-day plants. Short-day plants bloom in early spring or in the fall when there is more darkness and less daylight.

Like all organisms, plants compete with each other for the sunlight, water, and nutrients they need to live and grow. Each plant has its own strategy for winning the battle. Some plants grow higher than others for sunlight. Some plants make a poison that prevents other plants from growing near them. Other plants make chemicals that discourage animals from feeding on them.

Animals also have adaptations that help them survive in their environment. A powerful protector is an animal's ability to look like something else, called mimicry. An animal that does not move, or moves slowly, and looks like its surroundings is said to be camouflaged.

All living things respond to changes in their environment. They do these things in order to survive.