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9700 · 1.1

The microscope in cell studies — practice questions

Practice and worked examples for 9700 The microscope in cell studies. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

A student observes a chloroplast in an electron micrograph. The image of the chloroplast is 30 mm long. If the actual size of the chloroplast is 5 µm, calculate the magnification of the image.

Show solution outline
  1. Ensure consistent units: Convert the image size from mm to µm to match the actual size unit. 1 mm = 1000 µm Image size = 30 mm = 30 × 1000 µm = 30,000 µm
  2. State the formula: Magnification = Image size / Actual size
  3. Substitute values and calculate: Magnification = 30,000 µm / 5 µm Magnification = 6000

Therefore, the magnification of the image is x6000.

Worked example 2

A student calibrates an eyepiece graticule using a stage micrometer. They find that 40 eyepiece units (epu) correspond to 10 divisions on the stage micrometer. Each division on the stage micrometer is 10 µm. They then measure a red blood cell to be 3 epu in diameter. Calculate the actual diameter of the red blood cell.

Show solution outline
  1. Calculate the total known length on the stage micrometer: Length = 10 divisions × 10 µm/division = 100 µm
  2. Determine the value of one eyepiece unit (epu): We know that 40 epu = 100 µm. Therefore, 1 epu = 100 µm / 40 1 epu = 2.5 µm
  3. Calculate the actual size of the red blood cell: The cell measures 3 epu. Actual diameter = 3 epu × 2.5 µm/epu Actual diameter = 7.5 µm

Therefore, the actual diameter of the red blood cell is 7.5 µm.

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