Question 1 Medium
Change 0.25 mm into micrometres.
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Answer: 250 µm
- Multiply mm by 1000 to get µm.
- 0.25 × 1000 = 250 µm.
Microscopes and magnification: GCSE Combined Science Biology practice questions
A second set of questions on microscopes and magnification. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
An image is 60 mm long and the magnification is ×200. Calculate the real size in mm.
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Answer: 0.3 mm
- real size = 60 ÷ 200.
- The real size is 0.3 mm.
Question 3 Medium
Change 3 mm into micrometres.
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Answer: 3000 µm
- 1 mm = 1000 µm.
- 3 × 1000 = 3000 µm.
Question 4 Medium
An image is 12 mm long and the real size is 0.5 mm. Calculate the magnification.
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Answer: ×24
- Magnification = image size ÷ real size.
- 12 ÷ 0.5 = 24.
Question 5 Hard
A drawing of a cell is 25 mm long. The real cell is 5 µm long. Calculate the magnification.
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Answer: ×5000
- 25 mm = 25 000 µm.
- 25 000 ÷ 5 = ×5000.
Question 6 Hard
A bacterium is 2 × 10⁻³ mm long. Give its length in micrometres.
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Answer: 2 µm
- 2 × 10⁻³ mm = 0.002 mm.
- 0.002 × 1000 = 2 µm.
Question 7 Hard
An image is 18 mm long and the magnification is ×900. Calculate the real size in micrometres.
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Answer: 20 µm
- 18 ÷ 900 = 0.02 mm.
- 0.02 × 1000 = 20 µm.
Question 8 Hard
Why can an electron microscope show the inside of a mitochondrion but a light microscope cannot? Give one word for the property.
Show answer
Answer: resolution
- The structures are very small.
- Only a higher resolution can separate them.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is the equation for magnification?
Show answer
magnification = image size ÷ real size.
Check 2
What is resolution?
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The smallest distance between two points that can still be seen as separate.
Check 3
Why can an electron microscope show smaller structures than a light microscope?
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It has a higher resolution.
Check 4
Name two structures an electron microscope can show that a light microscope cannot.
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Ribosomes and the inside of mitochondria.
Check 5
Why is iodine added to a slide of onion cells?
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It stains the cells, so the nucleus and cell wall are easier to see.
Check 6
Why is a coverslip lowered at an angle?
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So that air bubbles are not trapped under it.
Check 7
Which objective lens do you start with on a microscope?
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The lowest-power lens.
Check 8
Which focus knob is used with a high-power lens?
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The fine focus knob.
Check 9
How many micrometres are in one millimetre?
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1000.
Check 10
How many nanometres are in one micrometre?
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1000.
Check 11
How do you change millimetres to micrometres?
Show answer
Multiply by 1000.
Check 12
How do you rearrange the magnification equation to find real size?
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real size = image size ÷ magnification.
Check 13
How do you rearrange the magnification equation to find image size?
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image size = real size × magnification.
Check 14
What is 0.002 mm in standard form?
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2 × 10⁻³ mm.
Check 15
Does magnification have a unit?
Show answer
No. It is written like ×200.
Check 16
Why must an electron microscope sample not be alive?
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It is viewed in a vacuum.
Check 17
What is magnification?
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How many times bigger the image looks than the real object.
Check 18
What does a light microscope use to form an image?
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Light and lenses.
Check 19
What does an electron microscope use to form an image?
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A beam of electrons.
Check 20
Why do you start with the lowest-power lens?
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It makes the specimen easier to find.
Check 21
What does the coarse focus knob do?
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It gives a rough focus. It is used with the low-power lens.
Check 22
How do you change micrometres to millimetres?
Show answer
Divide by 1000.
Check 23
What is standard form?
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A way to write very small or large numbers using powers of ten.
Check 24
What is a stain?
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A dye that makes parts of a cell easier to see.
Check 25
What is a scale bar?
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A line on a diagram that shows a real length.
Check 26
Why must both sizes be in the same unit in the magnification equation?
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Otherwise the answer is wrong, for example by a factor of 1000.
Check 27
Why estimate the size of a cell before calculating?
Show answer
To check that the final answer is a sensible size, within about the right power of ten.
Keep going with Microscopes and magnification
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