The idea that the basic unit of life is the cell is called the organismal theory cell theory

The correct answer will be cell theory.

Explanation:

Cell Theory is one of the basic theory of biology given by Matthias Schleiden and Theodor Schwann, in 1839 and revised and edited by Rudolph Virchow.

This theory describes the basic properties of all cells :

1. All living beings -unicellular or multicellular are composed of cells.  

2. The cell is the fundamental unit of life.

3. Cells arise from pre-existing cells (Omnis cellula-e-cellula).

Thus, the correct answer is cell theory.

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