Plants make their own food using a process called photosynthesis. A green coloured substance - chlorophyll, found in the chloroplasts of plant cells - traps light. Light energy is used to turn carbon dioxide (from the air) and water (from the soil) into glucose. Another product of photsynthesis is oxygen. It is called a by-product, because it is not used by plants (apart from in respiration) and it is released into the atmosphere, where it is then breathed in by humans and animals. Glucose provides energy for growth of the plant and it is also stored as starch for later use, because starch does not dissolve in water.
The chemical equation for photosynthesis is as follows:
In order for plants to grow, glucose is turned into cellulose to make new cell walls. Vegetable fats and oils are also made of glucose and stored for future use. We extract them from plants and use them for cooking.
Photosynthesis does not take place at night when there is no light from the sun, but it is possible to use artificial light. Farmers create conditions to increase the yield of their crops in greenhouses. They create optimum conditions for photosynthesis. The rate of photosynthesis depends on the availability of warmth, carbon dioxide and light intensity. The more of these, the higher the rate; but when the maximum rate is reached, it does not matter if light intensity and carbon dioxide concentration increase.
However, if the temperature exceeds the optimum (perfect) temperature, the photosynthesis rate decreases and even stops, because enzymes in the plant are denatured in high temperatures. The graphs below show how the rate of photosynthesis alters with different conditions: