The big idea of biology

The idea

The classical Cell Theory states that all living organisms are made of one or more cells, the cell is the basic unit of structure and function, and all cells arise from pre-existing cells.

A rule for all living things

A banyan tree, a crow and a bacterium in a drop of water look very different.

What do you think they all have in common in how they are built?

• All are made of one or more cells
• All have a backbone
• All have lungs

Build the Cell Theory

Slide the year forward from 1830. Watch each scientist add a piece.

The Cell Theory

According to the classical Cell Theory: (1) all living organisms are made up of one or more cells; (2) the cell is the basic unit of structure and function in living beings; (3) all cells arise from pre-existing cells.

This unifies all biology, from bacteria to humans, and explains life’s continuity through cell division.

• Scientist | Year | Finding
• Matthias Schleiden | 1838 | all plants are made of cells
• Theodor Schwann | 1839 | all animals are made of cells
• Rudolf Virchow | 1855 | new cells form only from pre-existing cells

Notes

The Cell Theory: all living organisms are made of one or more cells; the cell is the basic unit of structure and function; and all cells arise from pre-existing cells.

Check yourself

Which statement is part of the classical Cell Theory?

The Cell Theory says the cell is the…

Who stated that new cells are formed only from pre-existing cells?

• All cells arise from pre-existing cells — correct. Yes.
• Cells can form from non-living matter. That goes against the theory.
• Only plants are made of cells. All organisms are made of cells.
• basic unit of structure and function in living beings — correct. Yes.
• largest part of an organism. The cell is the basic unit.
• only part of plants. It applies to all living beings.
• Rudolf Virchow — correct. Yes, in 1855.
• Matthias Schleiden. He reported that plants are made of cells.
• Theodor Schwann. He found that animals are made of cells.