The cell theory was given by Schwann and Schleiden. The fact that cells can be observed in plants, animals, fungi, protists, bacteria and archea comes from one of the postulates of cell theory- All living organisms are composed of one or more cells.
Explanation:
The cell theory initially contained three postulates:
The cell is the basic unit of organization in all organisms.
All living organisms contain one or more than one cell.
All cells arise from cells which are already in existence.
The discovery of cell was made by Robert Hooke. Later after further observations, more points were added to the cell theory like
The genetic component of the cell is DNA and is transferred within cells.
The <em>chemical composition</em> of all the cells is similar.
A flow of <em>energy</em> occurs within the cells.
