Inside a cell.

Step 1 of 5

Cell theory

In 1665 Robert Hooke looked through a simple microscope at a slice of cork and saw little rooms. He called them “cells”. About two hundred years later, after looking the same way at plants, at animals and at tiny creatures in a drop of water, biologists put together cell theory:

• All living things are made of cells, one or many.
• The cell is the smallest unit that is alive.
• Every cell comes from another cell.

The Scene shows an animal cell, whole. A clear wrapping, and inside a thick fluid full of small bodies. The fluid is the cytoplasm, and the bodies, the parts that each have a job of their own, are called organelles.

Step 2 of 5

The power station

Look inside is at Cut open: the cell is cut open. Now you can pick one part in Look at, and the Scene lights it up and dims the rest.

Every cell needs energy all the time: to build, to move substances about and to make repairs. It gets that energy from sugar, which it breaks down with oxygen. The process is called cellular respiration, and it is not the breathing your lungs do: it happens inside every single cell.

Step 3 of 5

The protein factories

Most of what a cell does, proteins do: enzymes, channels, skeleton, hormones. The instructions for building each protein are written in DNA, which sits inside the nucleus, the big purple body. But the nucleus does not build the proteins itself: it sends copies of the instructions out.

Step 4 of 5

An organelle with no membrane

The nucleus has an envelope of two membranes, with pores the copies leave through. Mitochondria have two membranes too: a smooth outer one and a folded inner one. Is every part of a cell wrapped in a membrane?

Step 5 of 5

The membrane

The whole cell is wrapped in the cell membrane: a very thin double layer of fat molecules, with proteins set in it. It is flexible, and changes shape as the cell moves.