A-Level Biology Topic 12: Energy and Respiration MCQs – 30 Practice Questions with Answers (Cambridge 9700)
Free practice for Cambridge A-Level Biology 9700 on energy, ATP and respiration, with every question followed by a short worked explanation to help you check your understanding.
Energy Needs and ATP
Q1. Which processes illustrate the need for energy in living organisms?
- (A) Diffusion of gases across alveoli only in a typical human cell
- (B) Osmosis in root hair cells only
- (C) Passive movement of water only
- (D) Active transport, movement and anabolic reactions
Show Answer
Answer: D – Energy is needed for active transport, for movement, and for building reactions such as DNA replication and protein synthesis.
Q2. Why is ATP described as the universal energy currency of cells?
- (A) It is stored in large amounts in every cell during normal activity in the system described
- (B) It releases a small, usable amount of energy when hydrolysed and is easily regenerated
- (C) It is only used by animal cells
- (D) It carries oxygen around the body
Show Answer
Answer: B – ATP can be hydrolysed quickly to release energy where it is needed, then rebuilt, in all types of cell.
Q3. What happens when ATP is hydrolysed?
- (A) Energy is released as ATP is broken down to ADP and a phosphate group
- (B) Energy is stored as ADP joins with glucose in the system described for the organism involved
- (C) Oxygen is released from the ATP molecule
- (D) Carbon dioxide is produced from ATP
Show Answer
Answer: A – Hydrolysis of ATP to ADP and inorganic phosphate releases energy that can drive cellular work.
Q4. By which two routes is ATP synthesised in cells?
- (A) Glycolysis and the Krebs cycle only
- (B) Fermentation and diffusion only
- (C) Substrate-linked reactions and chemiosmosis
- (D) Photosynthesis and active transport only for the organism involved
Show Answer
Answer: C – ATP is made by transfer of phosphate in substrate-linked reactions and by chemiosmosis in mitochondrial and chloroplast membranes.
Q5. Where does chemiosmosis for aerobic respiration take place in a mitochondrion?
- (A) On the inner mitochondrial membrane
- (B) In the cytoplasm outside the mitochondrion
- (C) In the nucleus of the cell
- (D) On the outer surface of the cell membrane
Show Answer
Answer: A – The electron transport chain and ATP synthase involved in chemiosmosis are located in the inner mitochondrial membrane.
Q6. Which respiratory substrate gives the most energy per gram?
- (A) Carbohydrate, because it contains the most oxygen in most ordinary conditions
- (B) Protein, because it contains nitrogen
- (C) Glucose only, because it is the simplest sugar
- (D) Lipid, because it contains more hydrogen relative to oxygen
Show Answer
Answer: D – Lipids contain proportionally more hydrogen and less oxygen than carbohydrates, so more energy is released per gram on oxidation.
Q7. Why do proteins generally give a lower usable energy yield as respiratory substrates?
- (A) They contain no carbon atoms
- (B) Energy is spent removing nitrogen as a waste product before the rest can be respired
- (C) They cannot be broken down in cells at all during the process described under normal conditions
- (D) They are only used in photosynthesis
Show Answer
Answer: B – Proteins must first be deaminated, and dealing with the nitrogenous waste costs energy, reducing the net yield.
Q8. What is the respiratory quotient (RQ)?
- (A) The ratio of oxygen taken in to ATP produced under normal conditions
- (B) The ratio of glucose used to water produced
- (C) The ratio of carbon dioxide produced to oxygen taken in
- (D) The ratio of heat released to energy stored
Show Answer
Answer: C – RQ is defined as the number of molecules of carbon dioxide produced divided by the number of molecules of oxygen taken in.
Q9. What is the RQ for the aerobic respiration of a carbohydrate such as glucose?
- (A) 0.5
- (B) 1.0
- (C) 1.5
- (D) 2.0
Show Answer
Answer: B – Glucose respiration produces six molecules of carbon dioxide for six molecules of oxygen taken in, giving an RQ of 1.0.
The Four Stages of Aerobic Respiration
Q10. What is the RQ value expected when a lipid is respired aerobically?
- (A) Exactly 1.0, like carbohydrate
- (B) Greater than 1.0
- (C) Equal to the RQ of protein
- (D) Less than 1.0, around 0.7
Show Answer
Answer: D – Lipid respiration uses more oxygen relative to the carbon dioxide produced, so its RQ is below 1.0.
Q11. Where does glycolysis take place in a eukaryotic cell?
- (A) In the cytoplasm
- (B) In the mitochondrial matrix
- (C) On the inner mitochondrial membrane
- (D) In the chloroplast stroma
Show Answer
Answer: A – Glycolysis occurs in the cytoplasm, before any later stages inside the mitochondria.
Q12. Which outline correctly describes glycolysis?
- (A) Pyruvate is split directly into carbon dioxide and water for the organism involved under the conditions described in most ordinary conditions
- (B) Glucose is converted to acetyl coenzyme A in one step
- (C) Glucose is phosphorylated, split into two triose phosphate molecules, then oxidised to pyruvate, with ATP and reduced NAD formed
- (D) Glucose is built up into starch with ATP used
Show Answer
Answer: C – Glycolysis starts with phosphorylation of glucose, splits fructose 1,6-bisphosphate into two 3-carbon triose phosphates, and oxidises them to pyruvate.
Q13. Where do the link reaction and the Krebs cycle take place?
- (A) In the cytoplasm
- (B) On the outer mitochondrial membrane
- (C) In the chloroplast grana
- (D) In the mitochondrial matrix
Show Answer
Answer: D – Both the link reaction and the Krebs cycle occur in the mitochondrial matrix of eukaryotic cells.
Q14. What is produced when pyruvate enters the link reaction?
- (A) Glucose and oxygen only in most ordinary conditions
- (B) Acetyl coenzyme A, carbon dioxide and reduced NAD
- (C) Lactate and ATP only
- (D) Citrate and water only
Show Answer
Answer: B – In the link reaction pyruvate is decarboxylated and dehydrogenated, giving acetyl coenzyme A, carbon dioxide and reduced NAD.
Q15. What is the role of coenzyme A in the link reaction?
- (A) It carries the 2-carbon acetyl group into the Krebs cycle
- (B) It acts as the final electron acceptor
- (C) It splits glucose into triose phosphate during the process described
- (D) It pumps protons across the membrane
Show Answer
Answer: A – Coenzyme A transfers the acetyl group formed from pyruvate into the Krebs cycle as acetyl coenzyme A.
Q16. In the Krebs cycle, what happens when acetyl coenzyme A enters the cycle?
- (A) It combines with pyruvate to form glucose under normal conditions
- (B) It is converted directly to oxygen
- (C) Its 2-carbon fragment joins oxaloacetate to form citrate
- (D) It leaves the mitochondrion unchanged
Show Answer
Answer: C – Oxaloacetate, a 4-carbon compound, accepts the 2-carbon fragment to form citrate, a 6-carbon compound.
Q17. Which two types of reaction occur during the Krebs cycle?
- (A) Phosphorylation and photolysis only
- (B) Hydrolysis and condensation only
- (C) Polymerisation and denaturation only
- (D) Decarboxylation and dehydrogenation
Show Answer
Answer: D – Carbon dioxide is removed by decarboxylation and hydrogen is removed by dehydrogenation, reducing NAD and FAD.
Q18. What is the role of NAD and FAD in respiration?
- (A) They act as final electron acceptors during normal activity in the system described
- (B) They carry hydrogen to carriers in the inner mitochondrial membrane
- (C) They split water in the cytoplasm
- (D) They store glucose as glycogen
Show Answer
Answer: B – Reduced NAD and reduced FAD transfer hydrogen to the electron transport chain in the inner mitochondrial membrane.
Q19. Where does oxidative phosphorylation take place?
- (A) On the inner mitochondrial membrane
- (B) In the cytoplasm
- (C) In the mitochondrial matrix only in the system described
- (D) In the cell wall
Show Answer
Answer: A – Oxidative phosphorylation occurs on the inner membrane of mitochondria, where the electron transport chain is located.
Q20. What acts as the final electron acceptor in oxidative phosphorylation, and what forms?
- (A) Carbon dioxide, forming glucose
- (B) NAD, forming reduced NAD
- (C) Oxygen, forming water
- (D) Phosphate, forming ATP directly
Show Answer
Answer: C – Oxygen accepts electrons at the end of the chain and combines with protons to form water.
Anaerobic Respiration, Adaptations and Investigations
Q21. During oxidative phosphorylation, how do protons return to the mitochondrial matrix?
- (A) By active transport through the outer membrane
- (B) By facilitated diffusion through ATP synthase
- (C) By diffusion through the cytoplasm
- (D) By osmosis through aquaporins only
Show Answer
Answer: B – Protons pumped across the inner membrane flow back through ATP synthase, providing energy for ATP synthesis.
Q22. Why is the energy yield from aerobic respiration much greater than from anaerobic respiration?
- (A) Anaerobic respiration uses no glucose at all in most ordinary conditions during the process described under normal conditions
- (B) Anaerobic respiration produces only water
- (C) Aerobic respiration stores energy as starch
- (D) Aerobic respiration fully oxidises glucose, releasing far more energy through oxidative phosphorylation
Show Answer
Answer: D – In aerobic conditions glucose is completely broken down to carbon dioxide and water, while anaerobic breakdown stops early, leaving much energy in lactate or ethanol.
Q23. What happens in lactate fermentation in mammals?
- (A) Pyruvate is converted to lactate, regenerating NAD for glycolysis
- (B) Pyruvate is converted to ethanol and carbon dioxide during the process described
- (C) Glucose is converted directly to oxygen
- (D) Lactate is converted to citrate in the cytoplasm
Show Answer
Answer: A – Without oxygen, pyruvate accepts hydrogen to form lactate, which regenerates NAD so glycolysis can continue.
Q24. What happens in ethanol fermentation in yeast?
- (A) Pyruvate is converted to lactate only under normal conditions
- (B) Glucose is converted to starch only
- (C) Pyruvate is converted to ethanol and carbon dioxide
- (D) Ethanol is converted back to glucose
Show Answer
Answer: C – Yeast cells in anaerobic conditions convert pyruvate to ethanol, releasing carbon dioxide and regenerating NAD.
Q25. What is one advantage of anaerobic respiration despite its low yield?
- (A) It produces more ATP than aerobic respiration in a typical human cell
- (B) It can produce ATP quickly without oxygen when oxygen is scarce
- (C) It produces no waste products at all
- (D) It takes place only in mitochondria
Show Answer
Answer: B – Anaerobic respiration needs no oxygen and can supply ATP rapidly, for example in muscle during intense exercise, though the yield per glucose is small.
Q26. How does aerenchyma help rice grow with its roots submerged in water?
- (A) It stores starch in the leaves
- (B) It blocks water from entering the roots during normal activity
- (C) It increases the surface area of leaves
- (D) Its air spaces let oxygen move down to the submerged roots
Show Answer
Answer: D – Aerenchyma forms continuous air channels in roots and stems, allowing oxygen to diffuse to roots in waterlogged soil.
Q27. Which other adaptations help rice in waterlogged conditions?
- (A) Ethanol fermentation in roots and faster growth of stems
- (B) Lactate fermentation in leaves only
- (C) Closing all stomata permanently
- (D) Stopping respiration in the roots entirely in the system described
Show Answer
Answer: A – Rice roots can carry out ethanol fermentation when oxygen is scarce, and stems grow faster to keep leaves above water.
Q28. In a yeast respiration investigation using DCPIP, what does faster decolourisation show?
- (A) Slower respiration, because less hydrogen is released for the organism involved
- (B) Faster photosynthesis in the yeast
- (C) Faster respiration, because the indicator accepts hydrogen more quickly
- (D) No respiration at all in the yeast
Show Answer
Answer: C – DCPIP is a redox indicator that loses its colour when reduced by hydrogen released during respiration, so faster colour loss means a faster rate.
Q29. In a simple respirometer investigation, what effect does raising temperature have on the rate of respiration?
- (A) The rate falls steadily at all temperatures
- (B) The rate rises towards an optimum, then falls as enzymes denature
- (C) The rate stays exactly the same at every temperature
- (D) The rate rises without limit as temperature increases under the conditions described
Show Answer
Answer: B – Respiration is enzyme-controlled, so rate rises with temperature up to an optimum and then falls when enzymes denature.
Q30. Methylene blue is used as a redox indicator in yeast respiration investigations. What happens to it as respiration proceeds?
- (A) It gains oxygen and turns a deeper blue in most ordinary conditions
- (B) It is broken down into glucose
- (C) It evaporates from the mixture
- (D) It is reduced as it accepts hydrogen, losing its blue colour
Show Answer
Answer: D – Methylene blue accepts hydrogen released during respiration, becomes reduced, and loses its blue colour.
Work through any questions you missed again, then revise those areas before moving on to the next topic.