Answer – The 3 parts of cell theory are: all organisms are composed of cells; the cell is the most fundamental unit of structure and function in living beings; every cell is formed from other cells.

Explanation: 

In the late 1600s, scientist Robert Hooke observed cork under the then recently-invented microscope. He saw box-like structures all through and gave them the name cells. These cells formed the basis of classical cell theory proposed by botanist Matthias Schleiden and zoologist Theodor Schwann. The two reviewed their observations of plant and animal cells, and then provided the following two primary postulates of cell theory:

• All living beings are made up of cells. This could mean either a composition of a single cell or millions.
• The cell is the most basic structural and functional unit of every organism.

Rudolf Virchow then added on the third postulate relating to the origin of cells in 1859. His statement Omnis cellula e cellula meant that all cells come from pre-existing cells and are not the result of spontaneous generation.

With time, however, technological advances have allowed for further research and hence new findings. So in addition to the above postulates, these new ones have been added on to form the modern cell theory:

• The fundamental chemical composition of all cells is the same.
• DNA is passed on from one cell to another during cell division.
• Energy flow occurs within cells.

Biologists now use modern cell theory as the foundation for all cell-related studies and research.

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