Animal and plant cells share many similarities. For example, they both have: a nucleus, which houses the genetic material; a cytoplasm, where the chemical reactions of the cell occur; a cell membrane, which allows substances in and out of the cell; mitochondria, which release energy from respiration; and ribosomes which synthesise proteins that form the building blocks of of the cell. However there are some important additional features of plant cells. Plant cells have a cell wall. This is thick and maintains rigidity of the cell. They also have a vacuole which contains sap, and this allows the cell to remain swollen with water. Lastly, plant cells contain chloroplasts. These are small, vital structures that contain a green pigment which absorbs light energy. This unique adaption allows the photosynthesis reaction to occur inside the chloroplast, generating enough energy to meet the needs of the plant cell.