Types of microscopes and calculations

In a nutshell

Microscopes are devices we can use to zoom in or magnify very small objects. They’re very useful in looking at cells, as they are so small that we can’t see them with the naked eye.

Types of microscopes

Microscopes are used to view cells in much more detail. Different types of microscopes will produce varying levels of detail about the structure of a cell and its components.

Light microscopes

Light microscopes shine a light from the bottom of the microscope upwards towards the lens that you look at the cell with. With light microscopes, you can identify some structures such as the nucleus or cell membrane. However, to identify smaller structures or the internal details of a structure, you will have to use more powerful types of microscopes.

Electron microscopes

Electron microscopes can magnify cells much more than light microscopes can. This means they enable you to see inside substructures like mitochondria and ribosomes. However, electron microscopes require the sample to be in a vacuum to work; because there is no air, the sample cannot be living. Therefore, we cannot investigate cellular processes using an electron microscope. Electron microscope images also are only black and white, although colour can be added digitally later.

Biology; Key concepts; KS4 Year 10; Types of microscopes and calculations — A: Image from light microscope, 1. Basic outline of nucleus, 2. Basic outline of mitochondrion.

B: Image from electron microscope, 1. Detailed image of the internal structure of nucleus, 1. Detailed image of the internal structure of mitochondrion.

Microscopy calculations

We can use microscope images to work out the size of the cell or substructures using the following formula:

$magnification=\frac{image\ size}{actual\ size}$

When using calculations, it is important that to use the correct units. When measuring image size, we usually measure in centimetres or millimetres. However, the actual size of a cell is much smaller - we measure these in micrometres ( $\mu m$ ) or nanometres ( $nm$ ). Therefore, we need to know how to convert between units.

unit	equivalent unit
$1\,cm$	$10\,mm$
$1\,mm$	$1000\,\mu m$
$1\,\mu m$	$1000\,nm$

The conversion can be visualised as the following:

Biology; Key concepts; KS4 Year 10; Types of microscopes and calculations

Example

A cell is magnified $2500$ times. On paper, the image of the cell measures $20\ mm$ in diameter. Determine the actual size of the cell in micrometres.

$1\ mm = 1000\ \mu m$

Substitute the numbers in, making sure that the $mm$ unit measurement is converted into $\mu m$ :

$2500=\frac{20\times 1000}{actual}$

Rearrange the formula to get the actual size:

$actual\ size = \frac{20,000}{2500}$

Simplify:

$actual\ size = 8$

$\underline{Therefore,\ the\ actual\ size\ of\ the\ cell\ is\ 8\,\mu m.}$