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Cell Structure · Paper 2 — Free Biology HL Practice Questions

1MasterySAQ-SRole of ribosomes, mitochondria, and chloroplasts7 marksPaper 2~11 min
A researcher compares the efficiency of mitochondria from different tissues. Liver mitochondria consume 1.8×10−16 mol1.8 \times 10^{-16}\,\text{mol} of O2\text{O}_2 per second when respiring with excess substrate. Each liver mitochondrion contains 5000 copies of cytochrome c oxidase, the terminal enzyme of the electron transport chain.
(a)
State the final electron acceptor in the electron transport chain. [1 mark]
(b)
Explain how the electron transport chain establishes a proton gradient across the inner mitochondrial membrane. [2 marks]
(c)
Calculate the number of O2\text{O}_2 molecules consumed per cytochrome c oxidase molecule per second. (Avogadro's constant =6.02×1023 mol−1= 6.02 \times 10^{23}\,\text{mol}^{-1}.) Give your answer to 2 significant figures. [2 marks]
(d)
The researcher finds that muscle mitochondria consume O2\text{O}_2 at three times the rate of liver mitochondria but contain the same number of cytochrome c oxidase molecules. Deduce what this difference indicates about the rate-limiting step of oxidative phosphorylation in muscle mitochondria compared with liver mitochondria. [2 marks]
diagram

Solutions

2MasterySAQ-SRole of ribosomes, mitochondria, and chloroplasts6 marksPaper 2~9 min
A chloroplast in a leaf cell fixes 1.2×10−16 mol1.2 \times 10^{-16}\,\text{mol} of CO2\text{CO}_2 per second during peak sunlight. The Calvin cycle requires 3 molecules of ATP and 2 molecules of NADPH to fix one molecule of CO2\text{CO}_2.
(a)
State the location within the chloroplast where the Calvin cycle occurs. [1 mark]
(b)
Explain why the Calvin cycle is described as a cyclic process, referring to RuBP. [2 marks]
(c)
Calculate the rate of ATP consumption in the chloroplast in mol s−1\text{mol}\,\text{s}^{-1}. Give your answer in standard form to 2 significant figures. [1 mark]
(d)
Determine the ratio of ATP to NADPH consumed per molecule of CO2\text{CO}_2 fixed, and explain why a higher proportion of ATP than NADPH is required in the Calvin cycle. [2 marks]
diagram

Solutions

3ChallengeLAQOrganelles and their functions10 marksPaper 2~15 min

Data

- Healthy cell: 3232 ATP molecules produced per glucose molecule during complete aerobic respiration - Patient cell: 88 ATP molecules produced per glucose molecule - Oxygen consumption rate in patient cells: 15%15\% of the rate in healthy cells - Electron transport chain (ETC) complexes show normal activity when assayed in isolated inner mitochondrial membrane preparations from patient cells
A research team investigates a rare mitochondrial disorder in human fibroblasts. Cells from a patient show normal rates of glycolysis but significantly reduced overall ATP production. Electron microscopy reveals sparse, disorganised cristae and a less dense matrix compared with healthy cells.
(a)
Explain how sparse cristae could account for the reduced ATP yield observed in the patient cells. [4 marks]
(b)
The following two hypotheses have been proposed to explain the disorder. - Hypothesis 1: A mutation in the gene encoding ATP synthase reduces its catalytic activity. - Hypothesis 2: A defect in the mitochondrial inner membrane transporter reduces import of pyruvate into the matrix. Using all of the data provided, evaluate which hypothesis better supported. [6 marks]
diagram

Solutions

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