A plant is like a little factory. It will take several things, put them together with the help of light, and end up with something new. Making food by plants is called photosynthesis. This word can be broken into two words: photo meaning "light" and synthesis meaning "put together." Only green plants can take water from the soil, carbon dioxide from the air, and with the help of light, make sugar. Since plants do not use all of the oxygen for food-making, it is given off. Animals need plants for food and oxygen.
Photosynthesis is a chemical change which occurs in all green cells. Only green plants are able to take the sun's energy and put it into a stored form for use by other plants and animals. Scientists know most of the materials and steps involved in this wonderful process yet are still unable to accomplish this in the laboratory. There is a secret about green plant cells that man has not discovered as yet.
The electromagnetic energy contained in sunlight is converted by photosynthesis to chemical energy stored in the sugar molecule. The sugar can then be converted into starch and stored.
The rate of photosynthesis is dependent upon several conditions. A greater amount of water available will increase the rate of photosynthesis. Food-making occurs best in a temperature range from 68 °F to 110 °F. The amount of carbon dioxide present in the air is important. The air contains one-half per cent of carbon dioxide and a plant can use up to five per cent concentration, therefore this is a limiting factor. The amount and nature of the light controls photosynthesis. Food production is most active in about one-tenth of full sunlight. Too much light tends to destroy some of the products of photosynthesis.
Food manufactured in the leaves or other green parts of a plant is transported to various parts and stored for future use. Most annual plants store food in their seeds. Biennials and perennials also store food in their roots, stems, and leaves.
