Cells are the basic building blocks of all living things. They are the smallest form of life. Cells give all living things their structure and functionality, from bacteria to humans. A single cell is the source of all life. Single cells make up a variety of organisms. An organism’s total activity is the sum of its cell activities. The genetic makeup of every cell in the body is the same, but mature cells can become specialised to carry out particular tasks. A pre-existing cell always divides to create a new cell.