A bacterial cell.

Step 1 of 5

A different cell

The cells we have seen so far, plant and animal, are called eukaryotic: they have a nucleus and membrane-bound organelles. The bacterium in the Scene, E. coli, which lives in our gut, is built differently. It is prokaryotic, and far smaller too: 2 µm long and 1 µm wide, about twenty times smaller than one of our cells.

Part of its envelope is cut away, so you can see inside. Behind it spin flagella, thin tails that drive it through the liquid, and its surface bristles with pili, which it uses to hold on.

Step 2 of 5

Splitting in two

A bacterium reproduces by binary fission: it copies its DNA, lengthens, and its membrane and wall pinch in at the middle until two daughter cells come apart. Each one is identical to its mother.

Look inside is time here: from a newborn cell to its division.

Step 3 of 5

Within an hour

In good conditions, at body temperature with plenty of food, E. coli divides every 20 min. The chart beside the Scene shows how many cells one cell becomes in eight hours. Mind the axis: each line on it is ten times the one below.

Step 4 of 5

In the fridge

The bacterium’s enzymes set how fast it divides, and they work fast or slow depending on the temperature.

Step 5 of 5

Warmest is fastest?

Warmth speeds the enzymes up, but not without end: too hot, and proteins lose their shape. Temperature is free now, starting from room temperature. Watch the chart as you move it.