The number of chloroplasts varies from roughly 40 to 200 per photosynthetic cell. This is equal to roughly 500,000 chloroplasts for every square millimeter of leaf surface area.
Chloroplasts are plant cell organelles that synthesize carbohydrate molecules. Using carbon dioxide from the air and water from the soil, chloroplasts combine the smaller molecules into larger, more complex ones, such as glucose. This process requires energy, which is provided by sunlight. The productivity of a plant cell is directly related to the amount of sunlight it can absorb. Leaves, which tend to be broad and flat, have a lot of surface area, which maximizes the number of cells that are exposed to sunlight.