Microscopy and Magnification
Build confidence in Microscopy and Magnification for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Master the magnification equation (magnification = image size ÷ real size) and why electron microscopes reveal sub-cellular structures that light microscopes cannot resolve.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Microscopes let us see cells and their structures. Light microscopes use light and lenses, while electron microscopes use a beam of electrons.
Electron microscopes have much higher magnification and much higher resolving power, which is why they revealed sub-cellular structures such as ribosomes and the internal detail of mitochondria that light microscopes cannot show.
Magnification is calculated as image size divided by real size. The formula rearranges to give any of the three quantities, and the most common error is failing to convert units before substituting — millimetres and micrometres must not be mixed.
Revision notes
Light versus electron microscopes
Light microscopes are cheap, portable, and can view living samples, but their magnification and resolution are limited.
Electron microscopes have far greater magnification and resolving power, revealing sub-cellular structures in much finer detail, but they are large, expensive and cannot view living specimens.
The magnification calculation
Magnification = image size ÷ real size. Rearranged: real size = image size ÷ magnification.
Both sizes must be in the same units before you divide. Remember 1 mm = 1000 μm, so a 5 mm image is 5000 μm.
Standard form and units
Cell measurements are often given in standard form, such as 1.5 × 10⁻⁵ m.
Convert to a sensible unit before comparing values. Answers should be given in the unit the question asks for, and to an appropriate number of significant figures.
Key points
- Magnification = image size ÷ real size.
- Convert both sizes to the same units first.
- 1 mm = 1000 μm.
- Electron microscopes have higher magnification and resolution than light microscopes.
- Electron microscopes revealed sub-cellular structures in detail.
- Light microscopes can view living samples; electron microscopes cannot.
Worked examples
Example 1
A cell has a real diameter of 50 μm. Its image is 10 mm wide. Calculate the magnification. [3 marks]
Model answer
Convert the image size to micrometres: 10 mm = 10 000 μm (1 mark). Magnification = image size ÷ real size = 10 000 ÷ 50 (1 mark) = ×200 (1 mark).
Example 2
An image of a cell is 30 mm across at a magnification of ×1500. Calculate the real size in micrometres. [3 marks]
Model answer
Real size = image size ÷ magnification = 30 ÷ 1500 = 0.02 mm (1 mark). Convert to micrometres: 0.02 × 1000 (1 mark) = 20 μm (1 mark).
Example 3
Explain why electron microscopes allowed scientists to develop their understanding of sub-cellular structures. [2 marks]
Model answer
Electron microscopes have a much higher magnification and resolving power than light microscopes (1 mark), so they can reveal structures such as ribosomes and the internal detail of mitochondria that light microscopes cannot show (1 mark).
Common mistakes
Mixing millimetres and micrometres in the calculation.
Both measurements must be in the same unit before dividing. 1 mm = 1000 μm.
Inverting the formula.
Magnification is image ÷ real. Dividing the other way gives a value less than 1 for a magnified image.
Writing magnification with units.
Magnification has no units — write ×200, not 200 μm.
Confusing magnification with resolution.
Magnification is how much larger the image is; resolution is the ability to distinguish two close points.
Exam tips
- Convert units before substituting into the formula.
- Write the formula out before calculating.
- Give magnification as a × value with no units.
- Distinguish magnification from resolving power when comparing microscopes.
Key terms
- Magnification
- How many times larger the image is than the real object.
- Resolution
- The ability to distinguish two close points as separate.
- Micrometre
- One thousandth of a millimetre, symbol μm.
- Electron microscope
- A microscope using a beam of electrons, giving high magnification and resolution.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.