Microscopy and Magnification Calculations — AQA GCSE Biology

Microscopes let us see cells and their structures. This topic covers types of microscope and the magnification calculation.

Light and electron microscopes

• Light microscopes use light and lenses. They are cheap, portable and can view living cells, but have lower magnification (up to ~×2000) and lower resolution.
• Electron microscopes use a beam of electrons. They have much higher magnification and resolution, revealing fine detail such as the internal structure of mitochondria and chloroplasts. This improved understanding of sub-cellular structures.

Resolution (resolving power) is the ability to distinguish between two separate points — higher resolution gives a clearer, more detailed image.

The magnification equation

$$\text{magnification} = \frac{\text{size of image}}{\text{size of real object}}$$

Rearrange to find any value:

• real size = image size ÷ magnification
• image size = real size × magnification

Working with units

Convert so both measurements use the same unit:

• 1 mm = 1000 µm = 1 000 000 nm.

Express answers in standard form where appropriate, e.g. 0.0025 mm = 2.5 × 10⁻³ mm.

Worked example

An image of a cell is 50 mm wide at ×500 magnification. Real size = 50 ÷ 500 = 0.1 mm = 100 µm.

Exam tips

• Learn the magnification triangle and practise rearranging it.
• Always convert units before calculating, and watch for mm/µm/nm.
• Be ready to give answers in standard form.
• Know that electron microscopes have higher resolution and magnification than light microscopes.