The rate of photosynthesis may be measured by the quantity of carbon dioxide consumed per unit time, or by measuring the quantity of oxygen consumed per unit time. Since photosynthesis is a very complex process, the rate at which photosynthesis occurs is determined by the step that is occuring the most slowly. This step is then known as the rate-limiting step. Factors which affect the rate of photosynthesis include, light intensity, temperature and carbon dioxide concentration. Each factor affects a different rate-limiting step.