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Edexcel GCSE Biology

Required practicals essentials — Edexcel GCSE Biology revision

Free revision notes, key terms, common exam traps and 5 practice questions with answers. About 6 minutes to read.

Practicals to know

  • Microscopy: prepare a slide, focus low power first, calculate magnification.
  • Osmosis: potato cylinders in different sugar concentrations; calculate percentage change in mass.
  • Food tests: Benedict's (sugar, brick red), iodine (starch, blue-black), Biuret (protein, purple), ethanol emulsion (lipid, cloudy white).
  • Enzyme rate: effect of pH on amylase, tested with iodine.
  • Photosynthesis: pondweed and a lamp; count bubbles at different distances.

Exam technique

  • Always identify the independent, dependent and control variables.
  • Repeat readings and calculate a mean; ignore anomalies in the mean.
  • Mention safety: eye protection, care with hot water baths, wash hands after handling microbes.

Key terms

Independent variable
The one you change.
Dependent variable
The one you measure.
Control variable
Anything kept the same to keep the test fair.
Anomaly
A result that doesn't fit the pattern.
Aseptic technique
Procedures to prevent contamination of cultures, e.g. flaming loops, sealing plates.
Percentage change
A calculation comparing the size of a change relative to the starting value.

Common exam traps

  • Not stating a specific control variable — 'keep everything the same' scores nothing.
  • Forgetting repeats when asked how to improve reliability.
  • Mixing up Benedict's and iodine colour changes.

Practice questions with answers

  1. 1. Iodine solution turns blue-black in the presence of:

    • • Protein
    • • Starch
    • • Lipid
    • • Reducing sugar

    Answer: Starch

    Benedict's is for reducing sugar; Biuret for protein.

  2. 2. How do you improve the reliability of a results table?

    Answer: Repeat the readings and calculate a mean, ignoring anomalies.

    Repeats + mean is the standard answer.

  3. 3. In the pondweed photosynthesis practical, what is the dependent variable?

    Answer: The number of oxygen bubbles produced per minute (rate of photosynthesis).

    Distance from the lamp is the independent variable.

  4. 4. Which piece of apparatus estimates the number of plants in a field?

    • • Quadrat
    • • Pipette
    • • Potometer
    • • Burette

    Answer: Quadrat

    Place randomly, count, then scale up to the total area.

  5. 5. When using a microscope, which power should you start on to find your sample?

    • • Low power
    • • High power
    • • Oil immersion
    • • It doesn't matter

    Answer: Low power

    Low power gives a wider field of view, making it easier to locate the sample first.

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