The mesophyll layer of a leaf consists of photosynthetic parenchyma cells. These are specialized cells that contain chloroplasts, which are responsible for capturing light energy and converting it into chemical energy through the process of photosynthesis. The mesophyll layer is located between the upper and lower epidermis of the leaf and is where most of the photosynthesis in a leaf takes place. The photosynthetic parenchyma cells are typically thin and flat, with a large surface area that allows for maximum absorption of light. They are also closely packed together to facilitate the exchange of gases, such as carbon dioxide and oxygen, which are necessary for photosynthesis. Therefore, the mesophyll layer is a crucial part of a leaf's structure and plays a vital role in the plant's ability to produce energy through photosynthesis.