Answer:
because the cell is the smaller unit that has the properties of life
Step-by-step explanation:
There are three basic principles/statements that are the basis of the unified cell theory, which was proposed by Matthias Schleiden and Theodor Schwann in 1838. All living organisms are composed of cells (first principle), whereby cells can be considered as the basic, structural and organizational units of all organisms (second principle). Moreover, new cells always arise from existing cells (third principle). In consequence, the cell is the smaller unit that has the properties of life in order to carry out all metabolic processes including reproduction, growth, development, etc.