Question Constellation Sign up for free AQA · GCSE · Biology · Higher
Cell size and magnification
Figure 4 shows a special slide used to determine the size of a cell viewed using a microscope.
Move the two guides to the dashed endpoints of the cell image. The result uses the original paper scale.
Calculate the magnification of the cell shown in Figure 4.
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Marking points
- 1 Measures the printed cell image within the accepted 35-37 mm range.
- 2 Converts the measured image size to the same unit as the real cell size.
- 3 Uses 30 small scale divisions at 1.5 µm each to obtain a real size of 45 µm.
- 4 Applies magnification = image size ÷ real size with consistent units.
- 5 Gives 800 with no unit.
Full-mark answer
The printed cell image measures about 36 mm = 36 000 µm. The cell spans 30 small divisions, so its real size is 30 × 1.5 µm = 45 µm. Magnification = 36 000 ÷ 45 = 800, so the answer is ×800.
Why this answer loses marks
Treat the number of scale divisions as the real size and give the magnification a length unit.
Each division has a scale value, so real size must use both pieces of evidence; magnification itself has no length unit.