Cells are the basic units of all living things and contain several parts that allow them to function. The cell membrane separates the cell from its surroundings and regulates what enters and leaves while protecting the cell. In plant cells, a cell wall surrounds the membrane for additional support. Inside the cell is the cytoplasm, which contains organelles like mitochondria for energy production and ribosomes for protein synthesis. Chromosomes in the nucleus contain the cell's genetic information.