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AQA GCSE Biology — Required Practicals flashcards

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All ten AQA GCSE Biology required practicals: variables, the method steps that matter, safety, sources of error and improvements, expected results and the calculations each needs. Biology-only practicals and Higher Tier cards are marked.

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Learn deck · part of AQA GCSE Biology · written against: AQA GCSE Biology (8461) specification, version 1.0; Higher Tier and separate-science-only cards marked on the front. Updated 2026-10-10.

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  1. In the microscopy practical, why is only a very thin layer of onion epidermis put on the slide?
    So that light can pass through it and individual cells can be seen.

    Why: a thick piece has overlapping layers of cells that block the light and blur the image.
    Required Practicals › Microscopy
  2. Why is iodine solution added to onion cells, or methylene blue to cheek cells, before viewing them?
    To stain the cells so structures such as the nucleus stand out against the background.

    Why: most cell structures are almost colourless.
    Required Practicals › Microscopy
  3. Why is the coverslip lowered onto the slide at an angle, using a mounted needle?
    To avoid trapping air bubbles.

    Why: bubbles under the coverslip block the view and can be mistaken for cells.
    Required Practicals › Microscopy
  4. When focusing a light microscope, which objective lens should you start with, and why?
    The lowest-power objective.

    Why: it has the widest field of view, so the cells are easy to find before you switch to higher power and use the fine focusing knob.
    Required Practicals › Microscopy
  5. If a light microscope uses a mirror rather than a built-in lamp, why must it never be pointed at direct sunlight?
    Sunlight focused through the lenses can damage the eye.

    Why: the microscope concentrates the light straight into the eye at the eyepiece.
    Required Practicals › Microscopy
  6. Give four rules for a good biological drawing of cells seen under a microscope.
    Use a sharp pencil with clear, continuous lines and no shading, draw label lines with a ruler, and include a magnification or scale bar.

    Why: a drawing records what is actually seen, not an artistic impression.
    Required Practicals › Microscopy
  7. A microscope has a ×10 eyepiece lens and a ×40 objective lens. What is the total magnification?
    ×400

    Total magnification = eyepiece magnification × objective magnification = 10 × 40.
    Required Practicals › Microscopy
  8. The field of view of a microscope is 0.4 mm across, and 8 cells fit side by side across it. Estimate the width of one cell in micrometres.
    About 50 µm

    0.4 mm ÷ 8 = 0.05 mm, and 0.05 mm × 1000 = 50 µm.
    Required Practicals › Microscopy
  9. In the practical on antiseptics and bacterial growth, what are the independent and dependent variables? (not in Combined Science)
    Independent: the type (or concentration) of antiseptic or antibiotic; dependent: the size of the clear zone of inhibition around each disc.

    Why: a larger clear zone means more bacteria were killed or stopped from growing.
    Required Practicals › Microbiology
  10. Why is one paper disc soaked in sterile water and placed on the agar plate with the antiseptic discs? (not in Combined Science)
    It is a control: it shows that any clear zone is caused by the antiseptic, not by the paper disc itself.

    Why: without it, you could not rule out the disc or handling as a cause.
    Required Practicals › Microbiology

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About these cards

Review status: Second-reader reviewed, with corrections applied.

Checked against:

  • Topic outline follows the AQA GCSE Biology (8461) specification, version 1.0 (outline only; no specification text reproduced).
  • OpenStax Biology 2e, consulted as a reference; no text copied.
  • Also checked against AQA's GCSE Biology (8461) Required practical handbook, version 5.3 (July 2025), and USDA FoodData Central food composition data (CC0 1.0) (reference only; no text copied).

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