Temperature affects photosynthesis by allowing plants to photosynthesize (i.e., build up) and respire (i.e., break down) when there is optimum daytime temperature. It also enables plants to curtail the rate of respiration at a cooler night. With high temperatures, respiration increases and the products of photosynthesis are used faster than they are produced.
The rate of the chemical reactions during photosynthesis increases with temperature. However, temperatures above 40 C causes the process to slow down. This occurs because the enzymes involved in photosynthesis are sensitive to temperature. Additionally, low temperatures cause plants to grow poorly. It slows down photosynthesis, thus resulting in slower growth and lower yields.
Enzymes are easily affected by temperature. When it is too cold, they move around much slower, thus unable to allow for a reaction to occur. When it is too hot, the rate of reaction increases. Heat energy leads to more collisions between the substrate and the enzyme.
Different plants require different optimal temperatures to grow well. Plants that grow in colder climates grow best at low temperatures. For a certain number of days, buds of plants need to get exposed to chilling hours, which is below a critical temperature, to resume growth during spring. When dormant, they can withstand even lower temperatures. After the rest period, they become more vulnerable to weather conditions, especially cold temperatures.