KS3 / GCSE Biology: Microscopy

We can see objects as small as 0.1 millimeters, and that means we can just about see these lice eggs in our hair and tiny single-celled organisms like amoeba. But it's possible to see things much smaller than that if we use magnification.

There's three types of microscope: light, like this one here, and two types of electron microscopes, like those ones over there.

Light microscopes use light and mirrors and can see things as small as 400 nanometers. This allows us to get down to the world of the cell, and that means some pretty amazing things can be seen.

Here's an amoeba engulfing red blood cells and red and white blood cells moving through a tiny blood vessel. And human sperm. A leaf surface at 600 times magnification and the head of a dog tapeworm no bigger than a grain of rice. Plant cells crammed with chloroplasts. Look at these glucose crystals.

But light microscopes have a limit. Any object that's smaller than the wavelength of light appears blurred. But in the 1930s, a new kind of microscope was invented, which took our eyes further than they'd ever been before, to places we'd never seen before - the electron microscope.

The specimen is put in a vacuum and is viewed not by light waves but by a single beam of electrons that scans the surface, building up an image on a screen rather like a television picture. Because electrons have a wavelength 100,000 times smaller than light, electron microscopes can magnify objects up to 10 million times.

There are two types of electron microscopes: the transmission and the scanning. The scanning electron microscope scatters electrons across the surface of a specimen. It can magnify in incredible detail. This is a leaf surface under a scanning electron microscope. Both types of electron microscopes make black-and-white images, but these have been colourised to make them clearer and a lot more appealing to the eye.

Check out this fruit fly. A pubic louse and its claws. Cancer cells splitting. A blood clot. And human sperm cells on the surface of an egg.

But what about a transmission electron microscope? The difference with a transmission electron microscope is that it sees through things. It does this by sending beams of electrons, rather than light, through ultra-thin specimens. Using these microscopes, we're able to study the interior of cells and their organelles, and we've been able to get a better understanding of how pathogens, such as viruses, invade cells, like these HIV particles budding on the surface of a T cell.

Now a new type of electron microscope, a tunnelling electron microscope, has even made it possible to see the arrangement of atoms. Just how far will microscopy go?