This document defines and describes key parts of a cell including the chloroplast, cell membrane, nucleus, vacuole, cytoplasm, cell wall, and mitochondrion. The chloroplast contains chlorophyll and is where photosynthesis occurs to produce food. The cell membrane regulates what enters and exits the cell. The nucleus controls the cell's activities and is essential for reproduction. The vacuole stores substances. The cytoplasm fills most of the cell. The cell wall is the tough outer layer of plant cells made of cellulose. The mitochondrion releases energy from food.