Through photosynthesis, plants supply animals with two of their essential needs-food and oxygen, as well as removing carbon dioxide from the air. But remember that living cells, including plant cells, respire all the time, and they need oxygen for this. When the light intensity is high, a plant carries out photosynthesis at a much higher rate than it respires. So in bright light, there is an overall uptake of carbon dioxide from the air around a plant’s leaves, and a surplus production of oxygen that animals can use. A plant only produces more carbon dioxide than it uses up in dim light. We can show this as a graph of carbon dioxide exchanged at different light intensities.
The concentration of carbon dioxide in the air around plants actually changes throughout the day. Scientists have measured the level of carbon dioxide in the air in the middle of a field of long grass in summer. They found that the air contained least carbon dioxide in the afternoon, when photosynthesis was happening at its highest rate. At night when there was no photosynthesis, the level of carbon dioxide rose. This rise is due to less carbon dioxide being absorbed by the plants, while carbon dioxide was added to the air from the respiration of all organisms in the field.
Published in: Gardening