Most photosynthetic cells in plants are found in the leaves. Specifically, they are located in the mesophyll layer, which is the inner tissue of the leaf. The mesophyll is divided into two layers: the palisade mesophyll and the spongy mesophyll.
The palisade mesophyll is located just below the upper epidermis of the leaf and consists of tightly packed, elongated cells. These cells contain a high number of chloroplasts, which are the organelles responsible for photosynthesis. The spongy mesophyll, located below the palisade layer, has more loosely arranged cells with air spaces between them, allowing for gas exchange.
Chloroplasts within these cells contain chlorophyll, the pigment that captures light energy. This energy is then used to convert carbon dioxide and water into glucose and oxygen through the process of photosynthesis. The structure of the leaf, with its large surface area and thinness, maximizes the exposure of these cells to light, making the leaf the primary site for photosynthesis in plants.