# 1.1.5 Microscopy

### A Brief History of the Microscope

• Microscopy techniques have developed over time, increasing our understanding of cell subcellular structure
• The first light microscopes were developed in the 17th Century
• Scientists such as Anton van Leeuwenhoek and Robert Hooke are responsible for using microscopes to develop our first understanding of cells
• Light microscopes use light and lenses to form a magnified image of a specimen
• Over the centuries, the design of the light microscope has evolved, increasing magnification and resolution to enhance the detail of what can be visualised
• With a light microscope it is possible to see images of cells and large subcellular structures (like nuclei and vacuoles), although stains are often required to highlight certain parts of cells
• The first electron microscopes were developed in the first half of the 20th Century
• Electron microscopes use beams of electrons, rather than light, to visualise specimens
• The wavelength of an electron beam is much smaller than that of visible light, which gives electron microscopes a much higher resolution and magnification

### Electron Microscopes

• An electron microscope has much higher magnification and resolving power than a light microscope
• They can therefore be used to study cells in much finer detail, enabling biologists to see and understand many more subcellular structures such as the mitochondrion
• They have also helped biologists develop a better understanding of the structure of the nucleus and cell membrane

### Magnification Calculations

• Magnification is calculated using the following equation:
`Magnification = Drawing size ÷ Actual size`
• A better way to remember the equation is using an equation triangle:

An equation triangle for calculating magnification

• Rearranging the equation to find things other than the magnification becomes easy when you remember the triangle – whatever you are trying to find, place your finger over it and whatever is left is what you do, so:
• Magnification = image size / actual size
• Actual size = image size / magnification
• Image size = magnification x actual size
• Remember magnification does not have any units and is just written as ‘X 10’ or ‘X 5000’

#### Worked example

An image of an animal cell is 30 mm in size and it has been magnified by a factor of X 3000. What is the actual size of the cell?

To find the actual size of the cell:

Worked example using the equation triangle for magnification

#### Exam Tip

It is easy to make silly mistakes with magnification calculations. To ensure you do not lose marks in the exam:

• Always look at the units that have been given in the question – if you are asked to measure something, most often you will be expected to measure it in millimetres NOT in centimetres – double-check the question to see!
• Learn the equation triangle for magnification and always write it down when you are doing a calculation – examiners like to see this!

### Converting Units

• You may be given a question in your Biology exam where the measurements for a magnification calculation have different units. You need to ensure that you convert them both into the same unit before proceeding with the calculation (usually to calculate the magnification)
• For example:

Example of an extended magnification question

• Remember that 1mm = 1000µm
• 2000 / 1000 = 2, so the actual thickness of the leaf is 2 mm and the drawing thickness is 50 mm
• Magnification = image size / actual size = 50 / 2 = 25
• So the magnification is x 25

#### Exam Tip

If you are given a question with 2 different units in it, make sure you make a conversion so that both measurements have the same unit before doing your calculation. Also, watch out for the units you are given in the answer-prompt space.