Onion skin cells are a type of plant cell that are used for studying plant anatomy because they are easy to obtain and do not require special preparation. Unlike other plant cells, onion skin cells do not contain chloroplasts because they are located in the bulb of the onion plant, which grows underground and therefore has little exposure to sunlight. Chloroplasts are organelles that are responsible for photosynthesis, which is the process by which plants convert sunlight into energy. Since onion skin cells do not need to photosynthesize, they do not require chloroplasts. Instead, they contain a large central vacuole that provides turgor pressure to keep the cell rigid.