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IGCSEBiology
Trial Class

Original practice · 5 questions · 15 marks · about 17 minutes

Fermentation and Bioreactors Practice Questions

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

These questions test your understanding of how microorganisms are used in industrial processes, including the design of fermenters.

Before you open the answers

  • Attempt every question without notes.
  • Show working for calculations and write complete biological statements.
  • Use the suggested time as a guide, not a strict limit on the first attempt.

These are original practice questions. They do not reproduce an official Cambridge paper or official mark scheme.

  1. Question 1

    Paper 4 Extended 4 marks Difficulty 3/5

    Describe four features of an industrial fermenter (bioreactor) and explain the purpose of each.

    Show model answer and marking guidance
    1. Stirrer/paddle: mixes the contents to ensure even distribution of nutrients and microorganisms.
    2. Temperature control (water jacket): maintains optimum temperature for enzyme activity.
    3. Air supply (sterile): provides oxygen for aerobic respiration of microorganisms.
    4. pH monitor and control: maintains optimum pH for microbial growth.

  2. Question 2

    Paper 4 Both 3 marks Difficulty 3/5

    Explain why aseptic (sterile) technique is important when using a fermenter.

    Show model answer and marking guidance
    1. Prevents contamination by unwanted microorganisms.
    2. Contaminants could compete with the desired microorganism for nutrients.
    3. They could also produce toxins or waste products that spoil the product.

  3. Question 3

    Paper 4 Both 3 marks Difficulty 3/5

    Describe how yeast is used to make bread, explaining the role of anaerobic respiration.

    Show model answer and marking guidance
    1. Yeast is mixed with flour and water (dough).
    2. Yeast carries out anaerobic respiration: glucose → ethanol + carbon dioxide.
    3. The CO₂ gas gets trapped in the dough, forming bubbles that make it rise.

  4. Question 4

    Paper 2 Core 2 marks Difficulty 1/5

    Name two products made using fermentation by microorganisms.

    Show model answer and marking guidance
    1. Bread (using yeast).
    2. Beer / wine / yoghurt / cheese / antibiotics (any two valid).

  5. Question 5

    Paper 4 Extended 3 marks Difficulty 4/5

    Explain why the fermenter must control temperature carefully: what happens if the temperature is too low or too high?

    Show model answer and marking guidance
    1. Too low: enzyme activity is slow: microorganisms grow and produce product slowly.
    2. Too high: enzymes denature: microorganisms die, production stops.
    3. The optimum temperature gives the fastest rate of growth and product formation.

Mark the set consistently

Award a point only when the idea is clearly present in the written answer. Correct any missed point in a complete sentence, then test the same skill on a different question several days later.

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