Green plants use the sun's energy to manufacture their food. This process is called photosynthesis. It is essential for life on Earth. If there were no photosynthesis, oxygen would almost vanish from the Earth's atmosphere. There would soon be little food on Earth. Almost all forms of life would disappear. Some one-celled organisms, or living things, also make their own food through photosynthesis. These organisms include various bacteria and blue-green algae. The processGreen plants contain a pigment, or coloring substance, called chlorophyll. This pigment absorbs energy from sunlight. The light energy trapped by the chlorophyll is changed into chemical energy. A plant receives water from the soil and carbon dioxide gas from the air. The plant uses the energy from sunlight to convert the water and carbon dioxide into oxygen and carbohydrates such as sugar and starch. The carbohydrates are the plant's food. The oxygen is released into the air. Effects of photosynthesisAlmost all living things get their food from the carbohydrates produced by plants, either directly or indirectly. Plants perform another important function in using up carbon dioxide and producing oxygen. Humans and other animals breathe in oxygen and breathe out carbon dioxide. Through photosynthesis, plants manufacture the food we eat and the air we breathe. Photosynthesis is also responsible for the “fossil fuels” present in the Earth's crust. These fossil fuels are coal, oil, and gas. Photosynthesis produces substances that contain carbon. Hundreds of millions of years ago, the remains of plants were buried in the Earth's crust. Under the Earth's surface, the carbon in these remains was slowly converted to coal, oil, and gas. |