Food production: crops, micro-organisms, fermenters and fish farming – IGCSE Biology exam questions with mark scheme

1Grade 4–54 marks

A grower burns paraffin in a glasshouse during winter to increase the yield of tomato plants.

(a) Explain how burning paraffin increases the yield. [3]

(b) Suggest why adding even more paraffin heaters may not increase the yield further. [1]

(a) any three from: burning releases carbon dioxide; burning raises the temperature (in winter); carbon dioxide / temperature is a limiting factor (for photosynthesis); rate of photosynthesis increases; more glucose / sugar / starch made so more growth / biomass / bigger fruit — first point(1)
(a) second point(1)
(a) third point(1)
(b) another factor becomes limiting, e.g. light intensity (in winter) / water / minerals; accept temperature becomes too high so enzymes denature; accept carbon dioxide / pollutant gases reach harmful levels(1)
Answer: (a) releases CO₂ and heat, which were limiting photosynthesis, so faster photosynthesis and more growth (b) another factor (e.g. light) becomes limiting
Examiner tip: Link the gas to the process: 'more CO₂ for photosynthesis' scores; 'more CO₂ helps plants grow' does not.

2Grade 6–74 marks

Microorganisms are grown in an industrial fermenter to make a product.

(a) Explain why the fermenter has a water jacket. [2]

(b) Explain why the fermenter and nutrients are sterilised before use. [1]

(a) respiration of the microorganisms releases heat; allow microorganisms produce heat(1)
(a) water jacket removes heat / cools the fermenter to keep the temperature at the optimum (for growth / enzymes); allow stops enzymes denaturing / microorganisms being killed by overheating(1)
(b) to kill unwanted / contaminating microorganisms (which would compete with the culture / reduce the yield / contaminate the product / make toxins); allow to prevent contamination(1)
(c) to distribute / mix nutrients or oxygen or heat evenly (so all microorganisms get them) / keep the temperature even / keep microorganisms in suspension; any one; ignore 'to mix the contents' unqualified(1)
Answer: (a) removes heat released by respiration, keeping optimum temperature (b) prevent contamination by competing microbes (c) distributes nutrients, oxygen and heat
Examiner tip: Say where the heat comes from — respiration of the microorganisms — for the first mark in (a).

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