Newsademic British English edition 260

Part o f the cell, on the other side 
from where the light was shin­
ing, lit up. After this happened, 
the bacteria began to move away 
from the ‘bright light’. By doing 
this, they were moving towards 
the shining light.
The bacteria have small, hair­
like protrusions around the outside 
o f their single cells. These tiny hairs 
are called ‘pili’. The bacteria use 
their pili to move. The hairs hold 
on to whatever surface the bacteria 
are on and pull the cells forwards. 
These bacteria cannot swim. They 
use their pili to move across the sur­
face o f the water.
After they had watched the bacte­
ria moving, the scientists did several 
experiments. They used more power­
ful microscopes to look at the bacte­
ria and different types o f light. These 
experiments showed that the single 
cells ‘focused’ the incoming light 
on the far side of the cell. It is this fo­
cusing that creates the bright lights 
the scientists observed. The bacte­
ria then know to move in a direction 
away from the bright light they make.
These bacteria are three micro­
metres, or 0.003 millimetres (0.0001 
inches) across. Yet their cells are 
acting in the same way that an eye 
does. The bacteria cannot see im­
ages like a human eye. However, it 
can work out what is light and dark. 
W hen different forms o f life develop
similar things it is often called paral­
lel evolution, or convergent evolu­
tion. Sharks and dolphins are an ex­
ample o f this. A shark is a fish and a 
dolphin is a mammal. Yet, both have 
evolved to be good swimmers. This 
explains why they look similar.
The scientists are sure that the 
bacteria’s single cells are acting 
like a simple eye. If true, these or­
ganisms are probably the smallest 
and oldest examples o f ‘eyes’ in the 
world. The scientists now plan to 
find out if other bacteria can see in 
the same way. N ot all bacteria are 
round like an eye. Some are cigar­
shaped, or long and thin. □
M