Schleiden and Schwann both together discussed Schwann’s hypothesis and they formulated cell theory. The important aspects of cell theory are: 
 All living organisms are made up of minute units, the cells which are the smallest entities that can be called living. 
 Each cell is made up of protoplasm with a nucleus and bounded by plasma membrane with or without a cell wall. 
 All cells are basically alike in their structure and metabolic activities. 
Function of an organism is the sum total of activities and interaction of its constituent cells. 

All living beings are made up of cells cell is the structural and functional unit of life all cells arise from pre-existing cells