O Levels Biology (5090)•5090/12/M/J/19
Explanation
Microbial Waste Products in Fermentation
Steps:
- Identify the process in bread-making: Yeast ferments sugars to produce carbon dioxide gas, causing dough to rise.
- Identify the process in yogurt production: Bacteria convert lactose in milk to lactic acid, thickening and souring it.
- Match waste products to each: Carbon dioxide for bread, lactic acid for yogurt.
- Compare with options to select the matching pair.
Why B is correct:
- Fermentation by yeast in bread releases CO2 (C6H12O6 → 2C2H5OH + 2CO2), while lactic acid bacteria in yogurt produce lactic acid (C6H12O6 → 2CH3CHOHCOOH).
Why the others are wrong:
- A: Yogurt uses lactic acid, not CO2, for acidification.
- C: Bread uses CO2 for leavening, not lactic acid.
- D: Bread requires CO2 gas, not lactic acid, for rising.
Final answer: B
Topic: Anaerobic respiration
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