A-LevelBiologyEnergy and respirationOct/Nov 2019Paper 5 Q118 Marks
A group of students investigated the growth of different varieties of yeast. The students learned that the rate of respiration in a yeast culture is proportional to the biomass of the culture. Respiration rate can be used as a measure of the growth of a yeast culture. Respiration rates can be measured using the redox indicator TTC. • During respiration, hydrogen ions are removed from glucose to reduce hydrogen carriers such as NAD and FAD. • A redox indicator can be used as a hydrogen carrier in experimental conditions instead of NAD or FAD. • The colour change of the redox indicator can be measured using a colorimeter.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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