Question 1
Paper 1A style
Which statement about ATP is correct?
- It is a nucleotide containing deoxyribose.
- Energy is required to hydrolyse it to ADP and phosphate.
- It is a nucleotide, and its hydrolysis to ADP and phosphate releases energy.
- It moves freely out of cells through the plasma membrane.
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Answer: C [1]
Question 2
Paper 1A style
Which feature is shared by aerobic and anaerobic cell respiration in humans?
- Both produce carbon dioxide.
- Both require mitochondria.
- Both can use glucose as the substrate.
- Both produce lactate.
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Answer: C [1]
Question 3
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanHow many decarboxylations and oxidations occur in one turn of the Krebs cycle?
- One decarboxylation and two oxidations
- Two decarboxylations and four oxidations
- Two decarboxylations and three oxidations
- Four decarboxylations and two oxidations
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Answer: B [1]
Question 4
Paper 1B style
A respirometer containing 3.0 g of maggots and soda lime was kept at three temperatures. The distance moved by the liquid drop in 5 minutes was recorded. The capillary tube has a cross-sectional area of 0.80 mm². The data are for practice. (a) Calculate the rate of oxygen uptake per gram at 25 °C, in mm³ g⁻¹ min⁻¹. Show your working. [2] (b) Identify the independent and the dependent variable. [1] (c) Explain the trend shown in the data. [2]
| Temperature / °C | Mean distance moved / mm |
|---|---|
| 15 | 11 |
| 20 | 17 |
| 25 | 24 |
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- (a) volume = 0.80 × 24 = 19.2 mm³ [1]
- (a) 19.2 ÷ 5 ÷ 3.0 = 1.28 mm³ g⁻¹ min⁻¹ / 1.3 [1]
- (b) independent: temperature; dependent: distance moved by drop / rate of oxygen uptake (both needed) [1]
- (c) rate of oxygen uptake / respiration increases with temperature [1]
- (c) respiration is catalysed by enzymes; more kinetic energy so more frequent substrate–active site collisions [1]
- (c) (temperatures are below the optimum so) no denaturation [1]
- (c) [max 2]
Question 5
Paper 2A style
(a) State two processes in cells that use energy from ATP. [2] (b) Distinguish between cell respiration and gas exchange. [1]
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- (a) active transport across membranes [1]
- (a) synthesis of macromolecules / anabolism [1]
- (a) movement of the whole cell (e.g. muscle contraction, flagella) / movement of chromosomes [1]
- (a) [max 2]
- (b) cell respiration produces ATP from carbon compounds inside cells, whereas gas exchange is diffusion of O₂ and CO₂ between organism and environment OWTTE [1]
Question 6
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels mean(a) Outline the stages of glycolysis. [2] (b) Explain why yeast converts pyruvate to ethanol and carbon dioxide in anaerobic conditions. [2]
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- (a) phosphorylation of glucose using ATP [1]
- (a) lysis into two triose phosphates (3C) [1]
- (a) oxidation / removal of hydrogen, reducing NAD [1]
- (a) ATP formed; net yield 2 ATP (and 2 pyruvate) per glucose [1]
- (a) [max 2]
- (b) to regenerate NAD / reduced NAD is oxidised [1]
- (b) so glycolysis can continue producing (2) ATP [1]
- (b) no oxygen so reduced NAD cannot be oxidised by the electron transport chain [1]
- (b) [max 2]
Question 7
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain why lipids yield more energy per gram than carbohydrates in cell respiration, and why fatty acids cannot be used in anaerobic respiration.
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- lipids contain less oxygen / more oxidisable hydrogen and carbon (per gram) [1]
- so more reduced NAD (and ATP) produced per gram [1]
- fatty acids broken into acetyl groups that enter via acetyl CoA / bypass glycolysis [1]
- anaerobic respiration depends on glycolysis, which only uses carbohydrate / acetyl groups are oxidised only in the Krebs cycle, which needs oxygen (via the electron transport chain) to regenerate NAD [1]
- [max 3]
Question 8
Paper 2B style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain how ATP is produced by the electron transport chain and chemiosmosis in the mitochondrion.
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- reduced NAD (from glycolysis, link reaction and Krebs cycle) passes a pair of electrons to the first carrier [1]
- NAD is regenerated [1]
- electron transport chain / carriers located in the inner mitochondrial membrane / cristae [1]
- electrons pass from carrier to carrier, releasing energy [1]
- energy used to pump protons from matrix into intermembrane space [1]
- proton gradient / high H⁺ concentration in intermembrane space [1]
- protons diffuse back into matrix through ATP synthase (chemiosmosis) [1]
- ATP synthase couples energy from proton flow to phosphorylation of ADP [1]
- oxygen is the terminal electron acceptor [1]
- oxygen accepts electrons and protons forming (metabolic) water [1]
- allows continued flow of electrons along the chain [1]
- [max 7]