Question 1
Which gas, made by yeast, causes bread dough to rise?
- Oxygen
- Carbon dioxide
- Ethanol
- Nitrogen
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Answer: B (1)
Question 2
Describe the role of Lactobacillus in the production of yoghurt.
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- the bacteria respire / break down lactose (milk sugar) (1)
- to make lactic acid (1)
- which lowers the pH / makes the milk proteins clump so milk thickens (1)
- allow gives a sour taste
Question 3
A student investigated the effect of temperature on the rate of anaerobic respiration in yeast. She mixed yeast with sugar solution, added a layer of oil, and collected the gas in a syringe in a water bath. (a) Explain why a layer of oil was added. (b) State two variables she should control.
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- (a) oil stops oxygen entering the solution (1)
- so the yeast can only respire anaerobically (1)
- (b) any two from: volume of sugar solution / concentration of sugar / type of sugar / mass of yeast / time for collecting gas (1)(1)
- allow depth / volume of oil
- reject temperature (independent variable)
Question 4
In the investigation at 30 °C, 12 bubbles of gas were counted in 3 minutes. Calculate the mean number of bubbles produced per minute.
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- 12 ÷ 3 (1)
- 4 bubbles per minute (1)
Question 5
An industrial fermenter has a water jacket and stirring paddles. Explain the purpose of each of these features.
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- water jacket: cools the fermenter / keeps the temperature at the optimum (1)
- because respiration releases heat / heat would denature enzymes (1)
- paddles mix the contents so nutrients and oxygen are evenly distributed (1)
Question 6
Describe and explain the conditions needed in an industrial fermenter for the growth of micro-organisms.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | Describes and explains at least four conditions, with a clear reason for each linked to growth or enzyme activity, and accurate use of terms such as aseptic, optimum, oxygenation and agitation. |
| 2 | 3–4 | Describes at least three conditions with some explanation of why they are needed. |
| 1 | 1–2 | Names one or two conditions with little or no explanation. |
Indicative content
- aseptic precautions: sterilise equipment and nutrients to stop contamination by other microbes that compete or spoil the product
- nutrients such as glucose and nitrogen sources for growth
- optimum temperature, controlled with a cooling jacket, for fastest enzyme activity
- optimum pH, monitored with probes and controlled by adding acid or alkali, to avoid denaturing enzymes
- oxygenation: sterile air supplied for aerobic respiration, giving more energy for growth
- agitation: stirring so nutrients, oxygen and heat are evenly spread
Question 7
Biology only (what this means)
Biology only: only in International GCSE Biology. Double Award students can skip it. What the labels meanFish farmers keep fish of similar size together in separate tanks. Explain why this helps to increase the number of fish that survive.
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- larger fish of the same species eat smaller fish (1)
- this is intraspecific predation (1)
- keeping similar sizes together reduces this, so more fish survive / more fish to harvest (1)
Question 8
Biology only (what this means)
Biology only: only in International GCSE Biology. Double Award students can skip it. What the labels meanDescribe four ways in which a fish farmer can make sure fish grow quickly and stay healthy.
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- maintain water quality / oxygen / temperature / pH (1)
- control disease with medicines / vaccines / clean water (1)
- remove waste products by filtering the water (1)
- feed a balanced diet at the right frequency / amount (1)
- selective breeding of fast-growing fish (1)
- keep predators out / separate species (1)
- Max 4