(Latin: cella = chamber)

Whether it is a bacterium, a plant, or a human, each organism is made up of cells. A cell is the smallest component of an organism that is capable of sustaining itself and reproducing. A single cell is too small in order to be visible to the naked eye. It only becomes visible underneath a microscope, with multiple magnification.

Each cell has a membrane that is made up of liquid fat molecules and incorporated proteins and has a double-layer structure. The inside of the cell is made up of a clear fluid (cell plasma; Greek: plasma = formation) which contains the cellular organelles. The cellular organelles produce all of the substances the cell needs to sustain its life and to exercise its functions.

Inside the cell nucleus, the genetic material is located. It contains the genes which have been inherited from the parents.

Some organisms – like bacteria, for instance – are made up of one cell only. By contrast, the human body is made up of about 100 trillion cells. Each of these cells is responsible for a specific job. Some cells bond to each other to form a tissue unit, like the cells of the heart muscle, which together see to it that the heart can pump blood. Other cells are present as individual cells, such as the defense cells of the immune system. They are specialized in destroying bacteria, viruses and other pathogens.