ALL ABOUT ENERGY

Food chains and food webs are about energy. All living things need energy. Without it, they cannot grow, or move, or produce young.

Animals need energy to grow and reproduce. Wolf spiders produce many young, which they carry on their backs.

As we will see in the next chapter, plants get their energy from the Sun. They use light energy to make their own food.

Animals cannot make their own food. They have to eat to get energy. Some eat plants and others eat animals. Some eat both animals and plants. Ultimately, all the food animals eat comes from plants. And plants get their energy from the Sun. So all living things get their energy from the Sun.

Energy Losses

Plants use only a tiny amount of the energy that comes from the Sun. Some energy goes back into space. Some warms the land and oceans. Only 1 or 2 percent of the energy from the Sun is absorbed by plants.

This energy pyramid shows how energy is lost at each stage in a food chain.

Plants do not turn all this energy into new growth. Only about a tenth of the energy becomes plant material. So animals that eat plants get only a tenth of the energy that the plant got from the Sun.

Animals like this cheetah use a lot of the energy from their food for moving around.

Like plants, animals lose a lot of the energy they get from plants they eat. They turn only about a tenth of the energy they get from plants into meat. So animals that eat other animals get only a thousandth of the energy that the plant got from the Sun. Each stage of the food chain has less energy than the one before it. Because of this, there are more plants than plant-eating animals. And there are more animals that eat plants than animals that eat meat.