What is the cellular system for?

A cell is an elementary living unit that is capable of renewing itself. It is separated from other cells or from the external environment by a shell – a membrane and has a nucleus or its equivalent, which contains the bulk of the information that controls heredity. Living organisms have two types of cell organization. A simple type of structure is the cells of bacteria and blue-green algae, highly organized – the cells of all other living things, starting from lower plants, animals and humans, their structure is the cell nucleus, separated from the cytoplasm by the nuclear membrane. Thus, dead cells can replace each other.