Explain why the resolution of an electron microscope is greater than that of a light microscope.

OCR A-Level Biology A (H420) — 2.1 Cell structure · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Biologists use different types of microscopes to study cell ultrastructure. Transmission electron microscopes (TEMs) can resolve structures that are just a few nanometres apart, whereas the best light microscopes cannot resolve structures closer than approximately 200 nm.

Model answer (4 marks)

Resolution is limited by the wavelength of the radiation used.
Electrons have a much shorter wavelength than light.
A shorter wavelength means two points closer together can still be distinguished as separate.
Therefore the electron microscope can resolve / distinguish ultrastructure that the light microscope cannot.

Examiner tips

State the wavelength limitation first, then compare electron vs light wavelengths, explain effect on resolving power, finish with conclusion.
Use the exact wording from the mark scheme: "resolution is limited by the wavelength", "electrons have a much shorter wavelength", "shorter wavelength means two points can still be distinguished", "electron microscope can resolve ultrastructure".
Keep answer concise – 4 points, no extra explanation.

Common mistakes

Confusing resolution with magnification, or saying light microscopes have higher resolution. Using vague terms like "better" without linking to wavelength. Omitting the key point that electrons have a shorter wavelength than light.

Mark scheme (4 marks)

Resolution is limited by the wavelength of the radiation used
Electrons have a much shorter wavelength than light
A shorter wavelength means two points closer together can still be distinguished as separate
Therefore the electron microscope can resolve / distinguish ultrastructure that the light microscope cannot

Key terms in this question

resolution · electron microscope