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The key difference
Light microscopes use visible light and glass lenses, magnifying up to about ×1500 with lower resolution. Electron microscopes use beams of electrons, achieving magnifications over ×500 000 with much higher resolution, revealing fine internal cell structures.
Microscopes are essential tools in biology, and the two main types: light and electron: have very different capabilities. Understanding what each can and cannot reveal, and the meaning of magnification and resolution, is important for IGCSE Cell Biology questions.
Feature
Light Microscope
Electron Microscope
Source of illumination
Visible light
Beam of electrons
Maximum useful magnification
About ×1500
Over ×500 000
Resolution
Lower: about 200 nm (cannot distinguish objects closer than this)
Much higher: about 0.1 nm (can distinguish much finer detail)
Specimen
Can be living or dead; thin sections or whole small organisms
Must be dead; placed in a vacuum; often coated with heavy metals
Colour
Natural colours visible; stains can be used
Black and white images only (false colour can be added digitally)
Size and cost
Small, portable, relatively inexpensive
Very large, expensive, requires specialist training
What can be seen
Cells, nuclei, chloroplasts, large organelles, cell walls
All organelles including ribosomes, endoplasmic reticulum, cell membranes, fine details of mitochondria
Magnification vs Resolution
These two terms are often confused:
Magnification: how many times larger the image appears compared to the actual specimen. Calculated as: magnification = image size ÷ actual size
Resolution: the ability to distinguish between two points that are close together. Higher resolution means finer detail can be seen.
A light microscope can magnify an image greatly, but beyond about ×1500, the image becomes blurry because the resolution limit has been reached. Simply making the image bigger does not reveal more detail: it just makes the blur bigger. Electron microscopes have much higher resolution, so they can magnify much further while still showing clear detail.
The Magnification Formula
You must be able to use and rearrange this formula:
Magnification = Image size ÷ Actual size
Rearranged: Actual size = Image size ÷ Magnification
Units must match: convert mm to μm (×1000) or μm to mm (÷1000) as needed.
Example: An image of a cell is 30 mm long. The actual cell is 0.03 mm (30 μm) long. Magnification = 30 ÷ 0.03 = ×1000.
Try a comparison question (2 marks)
Explain why an electron microscope can reveal more detail about cell structure than a light microscope. [2]
Show the answer and marking guidance
Electron microscopes have a higher resolution than light microscopes: they can distinguish between two points that are much closer together
This means finer details / smaller structures (e.g. Ribosomes, endoplasmic reticulum) can be seen clearly, which are too small to be resolved by a light microscope
Original Cambridge-style practice written for this site.
Common comparison mistakes
When answering a compare question, write matched pairs rather than two separate descriptions.
Saying electron microscopes are better because they "magnify more": the key advantage is higher RESOLUTION, not just magnification
Confusing magnification with resolution: magnification makes things bigger; resolution makes things clearer
Forgetting that electron microscopes can only view dead specimens (placed in a vacuum)
Getting the magnification formula wrong: it is Image size ÷ Actual size, not the other way around