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Lesson: Chapter 6 — The Structure and Function of Plant and Animal Cells

6.1. The basic unit of life 2 of 2

What the cell theory says

The scientists who came after Hooke observed all sorts of living material under the microscope. In 1838 Schleiden, Schwann and Radolf Virchow gathered those findings together and put forward the cell theory.

This was not one person's single observation but a conclusion drawn from many observations of many organisms. It makes three claims.

The cell theory

  1. The cell is the structural as well as the functional unit of life.
  2. All living things are made of one cell or of cells.
  3. New cells arise from cells that already existed.

What each claim settles

Claim What it establishes
Structural and functional unit A cell is not only the smallest piece a living body is built from; it is also the smallest piece in which the business of living gets done.
All living things Plants, animals and organisms made of a single cell are all subject to the same one rule.
From cells that already existed A cell does not appear out of nothing. Every cell comes from the division of a cell that was already there.

The third claim decides the whole chapter

"New cells arise from cells that already existed" is another way of saying that organisms grow, wounds heal and one generation follows another entirely by cell division. Section 6.5 is about nothing else.