By what criterion all organisms are divided into unicellular and multicellular.

Single-celled organisms are organisms that consist of just one cell. Multicellular organisms are organisms that are made up of a system of cells. Therefore, organisms can be immediately divided into unicellular and multicellular organisms. In addition, multicellular organisms can live when some cells die off. In their place, live and healthy cells are formed. Unicellular organisms, for obvious reasons, die when the cell is damaged or the life cycle ends. Therefore, the criterion for dividing organisms is the number of cells.