Robert%20Hooke%2C%20in%20the%20year%201665%20discovered%20a%20cell%20using%20a%20microscope.%20It%20is%20the%20basic%20structural%20and%20functional%20unit%20of%20life.

Hooke%20was%20the%20first%20person%20to%20study%20a%20living%20thing%20under%20a%20microscope%20and%20examined%20a%20thin%20slice%20of%20cock%2C%20which%20looks%20like%20a%20honeycomb-like%20structure.%20He%20later%20called%20the%20structure%2C%20cells.

There%20are%20three%20tenets%20to%20the%20cell%20theory%3A

All%20living%20organisms%20are%20composed%20of%20one%20or%20more%20cells.

Cells%20arise%20from%20pre-existing%20cells.

The%20cell%20is%20the%20basic%20unit%20of%20structure%20and%20organization%20in%20organisms.

%3Ca%20class%3D%22mention%22%20data-mention%3D%22%23sciencefacts%22%20data-user-id%3D%22XWlyjFbhgqEL%22%20href%3D%22/topic/sciencefacts%22%3E%23sciencefacts%3C/a%3E%20%3Ca%20class%3D%22mention%22%20data-mention%3D%22%23Science%22%20data-user-id%3D%226RhBHV5lGAXq%22%20href%3D%22/topic/science%22%3E%23Science%3C/a%3E%20%3Ca%20class%3D%22mention%22%20data-mention%3D%22%23CellTheory%22%20data-user-id%3D%22kAywSEJ8speU%22%20href%3D%22/topic/celltheory%22%3E%23CellTheory%3C/a%3E%26nbsp%3B