Cell: The Unit of Life
Cell Theory
Cell theory says two things: every living thing is made of cells, and every cell comes from a cell that already existed.
Schleiden studied plants and Schwann studied animals, and together they proposed that all living things are built from cells. That was the first half of the idea.
But they could not explain where new cells came from. Virchow added the missing piece: a cell forms only by the division of an existing cell. Put together, that is cell theory as we use it today.
Where students slip up
The trap is thinking cells can appear on their own from non-living matter. They cannot. Every cell is made by an existing cell dividing. This is exactly the point Virchow added, and it is why the line 'every cell from a cell' is worth remembering.
Hold onto this
All life is cells. Every cell comes from a cell.
Why it helps in the exam: remember who added what. Schleiden (plants) and Schwann (animals) gave the first part, and Virchow added that cells arise only from existing cells.
Where this connects
This one rule quietly rules out life appearing from nothing, and it underlies everything from how a wound heals to how a tumour grows: all of it is existing cells dividing. The moment cells divide without the normal controls, you get cancer.
Quick check
Which scientist added that new cells arise only from pre-existing cells?
- ASchleiden
- BSchwann
- CVirchow
- DRobert Hooke