Why put oil on the yeast suspension?
Reveal answer
Keeps oxygen out → anaerobic.
Key words: oxygen
6(a) FOOD PRODUCTION · RECALL
6.6 Anaerobic respiration by yeast
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Why boil the glucose solution first?
Reveal answer
Removes dissolved oxygen.
Key words: dissolved
Measure yeast respiration rate?
Reveal answer
Gas syringe volume of CO₂ per minute (or bubbles).
Key words: gas syringe
What is meant by the term rate of respiration?
Reveal answer
The amount of carbon dioxide produced (or glucose used) per unit time.
Key words: rate of respiration
What is meant by the term liquid paraffin?
Reveal answer
An oily layer used to stop oxygen dissolving into a solution.
Key words: liquid paraffin
Measuring carbon dioxide release: for Counting bubbles, give the advantage and the limitation.
Reveal answer
Advantage: Simple, cheap. Limitation: Bubble size varies; less accurate.
Key words: Counting bubbles
Measuring carbon dioxide release: for Gas syringe, give the advantage and the limitation.
Reveal answer
Advantage: Measures volume accurately. Limitation: Plunger may stick; more expensive.
Key words: Gas syringe
Measuring carbon dioxide release: for Inverted measuring cylinder, give the advantage and the limitation.
Reveal answer
Advantage: Measures volume. Limitation: Some CO₂ dissolves in water.
Key words: Inverted measuring cylinder
Measuring carbon dioxide release: for Limewater or indicator colour change, give the advantage and the limitation.
Reveal answer
Advantage: Shows CO₂ presence. Limitation: Only qualitative or semi-quantitative.
Key words: Limewater or indicator colour change
True or false, and why? “The paraffin layer feeds the yeast.”
Reveal answer
False. It excludes oxygen so respiration is anaerobic.
True or false, and why? “Counting bubbles measures volume accurately.”
Reveal answer
False. Bubble size varies; collecting gas gives a volume.
True or false, and why? “Yeast dies at 40 °C.”
Reveal answer
False. The rate falls above the optimum as enzymes denature; the exact temperature varies with yeast strain.
What is a suitable control experiment for the yeast respiration practical?
Reveal answer
A tube with boiled (dead) yeast in the same glucose solution.
Key words: boiled
Why cool the boiled glucose solution before adding the yeast?
Reveal answer
High temperature would denature the yeast enzymes or kill the yeast.
Key words: denature
Which test shows that the gas released by yeast is carbon dioxide?
Reveal answer
Limewater turns cloudy (milky).
Key words: limewater