A cell is a membrane-bounded compartment that is filled with solutions of chemicals and water. Cells are the fundamental units of life.
Individual cells consume energy, and perform other metabolic chores necessary for their survival.
Some creatures, like bacteria, are comprised of only a single cell. Complex organisms like humans consist of hundreds of millions of cooperating cells, which through a process of differentiation, specialize to form bodily organs like the heart, lungs, liver, and skin. The cells of the human body communicate with their immediate neighbors and distant cells through chemical mediators such as local growth factors, hormones that are released into and carried through the bloodstream, and electrical signals that are transmitted through the cells we call nerves. Malignant, i.e. cancerous, cells differ from healthy cells in structure, function, appearance, metabolism, and their relationships with other cells. Cells reproduce through division, which is the primary mechanism of human tissue growth and replenishment.