and nitrogen into the air and soil. In this way, matter flows between living and non-living parts of ecosystems. The carbon cycle is explained in more detail in Chapter 39: Cycles on Earth. Matter also flows through ecosystems when one organism eats another.
The flow of energy through ecosystems As you will learn in Chapter 30: Energy, there are several different forms of energy. The sun is the main source of energy on Earth. It provides us with light and heat energy. Without it, life on Earth would be impossible. The energy from the sun is changed into many useful forms. Some of it is used by green plants to make food by photosynthesis. Photosynthesis allows plants to obtain energy from the sun. When plants are eaten the energy they contain passes on to other organisms.
Energy
Energy
Energy Fig. 17 The flow of energy through ecosystems.
Photosynthesis Photosynthesis is the way that plants make food using the sun’s energy. Photosynthesis converts light energy into chemical energy. This chemical energy is stored in glucose or starch within the plant. When plants are eaten, the matter and the energy they contain is passed on to other organisms.
Light energy
Photosynthesis
Chemical energy
Fig. 18 Light energy from the sun is converted to chemical energy by photosynthesis.
Respiration Plants and animals release energy from food by respiration. Respiration converts chemical energy into other forms. In animals the chemical energy in food may be converted into heat, motion, chemical and sound energy. This energy is lost from the ecosystem. Respiration also releases carbon dioxide and water into the atmosphere. These gases are matter which can be reused by other living organisms, usually plants.
