Cell theory: three ideas about cells

0:00What are all living things made of? The answer starts with a microscope.

0:06In 1665, the scientist Robert Hooke looked at a thin slice of cork through a microscope.

0:13He saw rows of tiny empty boxes and called them cells. They were the walls of dead plant cells.

0:21Since then, scientists have found cells in every living thing. They summed this up in three ideas, called cell theory.

0:29Idea one: living things are made of one or more cells.

0:35A unicellular living thing, like a bacterium, is made of just one cell.

0:41A multicellular living thing, like a plant or an animal, is made of many cells.

0:47Idea two: all cells come from pre-existing cells. Pre-existing means cells that were already there.

0:56A cell grows, then splits into two new cells. This is called cell division.

1:02A common mistake is to think cells can form from non-living matter. They cannot.

1:09Every new cell comes from a cell that already existed.

1:13Idea three: the cell is the basic unit of life.

1:18Basic unit means the cell is the smallest part of a living thing that is itself alive.

1:25Each cell takes in nutrients, the substances it needs to live and grow, and gets rid of waste.

1:33So, cell theory says: living things are made of cells, all cells come from pre-existing cells, and the cell is the basic unit of life.