A-LevelBiologyEnergy and respiration9700/42 · May/June 2020 · Q712 Marks
Define the term respiratory quotient (RQ).
- (a)Define the term respiratory quotient (RQ).[2]
- (b)(i)Fig. 7.1 summarises the respiration of an organic substance, A, in aerobic conditions. Complete Fig. 7.1 in the spaces provided. C18H32O2 + ..........02 --> ..........CO2 + 16H2O [Figure 7.1][2]
- (b)(ii)Calculate the RQ for substance A. Write your answer to two decimal places. RQ =[1]
- (b)(iii)Use your calculated RQ value to suggest the group of compounds to which substance A belongs.[1]
- (c)(i)Dinitrophenol (DNP) is a compound used in the production of a number of products, including chemical dyes, insecticides and wood preservers. People who work in factories with DNP are at risk of exposure if they do not follow health and safety guidelines. DNP is a molecule that can transport protons across the inner mitochondrial membrane, allowing protons to leak out of the intermembrane space. Suggest and explain the effects of DNP on aerobic respiration in human cells.[4]
- (c)(ii)Suggest two symptoms that may be experienced by people after exposure to DNP for several months.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [2] volume of carbon dioxide produced ÷ volume of oxygen consumed ;
- per unit time;
- [2] 25;
- 18;
- [1] 0.72;
- [1] lipid / fatty acid;
- [4] any four from:
- 1 ETC / electron transport chain, functions as normal;
- 2 H+ / protons, pumped into intermembrane space ;
- 3 proton gradient established ;
- 4 most, H+ / protons, diffuse through, DNP ;
- 5 into matrix ;
- 6 less / fewer, H+ / protons, pass through ATP synthase ;
- 7 less ATP produced ;
- [2] any two from:
- 1 tiredness;
- 2 weight loss;
- 3 increased, heart rate / breathing rate
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