# Explain why the resolution of a transmission electron microscope (TEM) is far greater than that of a light microscope, and explain how this improved resolution allows biologists to study cell ultrastructure in detail.

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

> A researcher wishes to investigate the internal membrane systems of a pancreatic exocrine cell, including structures such as the rough endoplasmic reticulum and Golgi apparatus. They must choose between a light microscope and a transmission electron microscope for their study.

## Mark scheme (4 marks)

1. The TEM uses electrons rather than light, and electrons have a much shorter wavelength than visible light.
2. Resolution is limited by the wavelength of the radiation used; a shorter wavelength gives a higher resolution / smaller minimum resolvable distance.
3. The higher resolution of the TEM means that structures smaller than the resolution limit of a light microscope can be distinguished, such as unit membranes / ribosomes / cristae.
4. Biologists can therefore study the arrangement and fine detail of internal membrane systems (e.g. the rough ER or Golgi apparatus) because closely adjacent membranes can be resolved as distinct structures.

## Key terms

- [resolution](https://www.gradenine.co.uk/glossary/resolution)
- [transmission electron microscope](https://www.gradenine.co.uk/glossary/transmission-electron-microscope)
- [ultrastructure](https://www.gradenine.co.uk/glossary/ultrastructure)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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