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AQA GCSE · Question 04.5 · Cell Biology
Figure 4 shows what the student saw using the microscope at a magnification of ×400. Line A–B in Figure 4 shows the length of cell Z.
Calculate the real length of cell Z. Complete the following steps.
- Measure the length of line A–B in millimetres (mm).
- Give your measurement of the length of line A–B in micrometres (μm). (1 mm = 1 000 μm)
- Calculate the real length of cell Z using the equation:
real length of cell Z (in μm) = length of line A-B (in μm) / magnification
Figure 4 shows what the student saw using the microscope at a magnification of ×400. Line A–B in Figure 4 shows the length of cell Z.
Calculate the real length of cell Z. Complete the following steps.
- Measure the length of line A–B in millimetres (mm).
- Give your measurement of the length of line A–B in micrometres (μm). (1 mm = 1 000 μm)
- Calculate the real length of cell Z using the equation:
real length of cell Z (in μm) = length of line A-B (in μm) / magnification
How to approach this question
1. Use a ruler to measure the red line A-B in the image. Write this down in mm. (For this online version, assume the length is 50 mm).
2. Convert your measurement from millimetres (mm) to micrometres (μm) by multiplying by 1000.
3. Take the image length in μm (from step 2) and divide it by the given magnification (×400).
4. The result is the real length of the cell in μm.
Full Answer
1. Length of line A-B = **50 mm** (Note: this may vary slightly on different screens, but we will use 50mm as the standard for this question).
2. Length of line A-B = 50 mm × 1 000 = **50 000 μm**.
3. Real length of cell Z = 50 000 μm / 400 = **125 μm**.
This calculation uses the magnification formula: **Magnification = Image Size / Actual Size**. We need to find the Actual Size (real length).
**Step 1: Measure the image size.**
Using a ruler on a standard printout, the line A-B measures approximately 50 mm. We will use this value.
*Image length = 50 mm*
**Step 2: Convert the image size to micrometres (μm).**
The question states 1 mm = 1 000 μm.
So, 50 mm = 50 × 1 000 = 50 000 μm.
*Image length = 50 000 μm*
**Step 3: Calculate the real length.**
Rearranging the formula: **Actual Size = Image Size / Magnification**.
The magnification is given as ×400.
Real length = 50 000 μm / 400
Real length = 500 / 4 = 125 μm.
*The real length of cell Z is 125 μm.*
Common mistakes
✗ Forgetting to convert mm to μm, leading to a very small and incorrect answer (50 / 400 = 0.125).\n✗ Dividing magnification by image size instead of the other way around.\n✗ Measurement errors (though a small range is usually accepted).
Practice the full AQA GCSE Biology Foundation Tier Paper 1
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