The three inputs of photosynthesis are carbon dioxide, water and sunlight. During photosynthesis, plants used the sun's energy to change water and carbon dioxide into glucose, a carbohydrate energy source. Oxygen, a by-product of the process, is released into the air.
Water enters a plant primarily through its roots, while carbon dioxide comes in through leaf pores called stomata. Plant cells also have organelles called chloroplasts. A chemical in the chloroplasts, chlorophyll, gathers the sunlight.
If the amount of one of the inputs is low, photosynthesis is slowed down, regardless of the quantities of the other inputs. Also, extreme heat or cold make it difficult for plants to undergo photosynthesis.