A Level Biology (A2) chapter 1: Energy and respiration MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
56 exam-style questions on Energy and respiration, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Which gives the usual order of energy value per gram of respiratory substrate, from highest to lowest?
A
carbohydrate, protein, lipid
B
lipid, protein, carbohydrate
C
lipid, carbohydrate, protein
D
protein, lipid, carbohydrate
Show answer
Answer: B. Typical values are about 39 kJ g−1 for lipid, 17 kJ g−1 for protein and 16 kJ g−1 for carbohydrate. Protein is only slightly higher than carbohydrate.
2. Palmitic acid is respired aerobically: C16H32O2 + 23O2 → 16CO2 + 16H2O. What is the RQ?
A
1.00
B
1.44
C
0.70
D
0.35
Show answer
Answer: C. RQ = 16 ÷ 23 = 0.70, typical of lipids. 1.44 is the ratio upside down, and 1.00 compares carbon dioxide with water instead of with oxygen.
3. How is the inner membrane of a mitochondrion adapted for oxidative phosphorylation?
A
it is freely permeable to protons, so they can diffuse quickly from the intermembrane space to the matrix
B
it is folded into cristae, giving a large area for electron carriers and ATP synthase
C
it holds the enzymes of the Krebs cycle attached to its outer surface
D
it contains circular DNA and 70S ribosomes that make ATP
Show answer
Answer: B. Folding into cristae increases the surface area for electron transport chains and ATP synthase. The membrane must be impermeable to protons so that a gradient can build up, and the Krebs cycle enzymes are in the matrix.
4. A chemical makes the inner mitochondrial membrane leaky to protons, so they can pass back into the matrix without going through ATP synthase. What is the effect?
A
ATP synthesis falls, but electron transport and oxygen uptake continue
B
electron transport stops, so oxygen uptake falls to zero
C
ATP synthesis rises because protons enter the matrix faster than before
D
protons build up in the intermembrane space, so more ATP is made by ATP synthase
Show answer
Answer: A. The proton gradient is lost, so little ATP is made and the energy is released as heat instead. Electron transport is not blocked, so electrons still flow to oxygen and oxygen uptake continues.
5. Methylene blue is added to a suspension of yeast in glucose solution. After some time the blue colour disappears. Why?
A
hydrogen removed by dehydrogenase enzymes reduces the methylene blue
B
oxygen released by the yeast cells oxidises the methylene blue to a colourless form
C
carbon dioxide from the yeast lowers the pH, and the acid bleaches the dye
D
the yeast absorbs the methylene blue and respires it
Show answer
Answer: A. Dehydrogenases remove hydrogen from respiratory substrates; methylene blue can accept this hydrogen, becoming reduced and colourless. The faster the colour is lost, the faster the rate of respiration.
6. A poison stops reduced NAD from passing its hydrogen to the carriers in the inner mitochondrial membrane. What happens to the Krebs cycle?
A
it slows and stops because oxidised NAD runs out
B
it continues at the same rate, using FAD instead of NAD
C
it speeds up because reduced NAD builds up in the matrix
D
it continues because it does not use oxygen directly
Show answer
Answer: A. The Krebs cycle needs oxidised NAD for its dehydrogenation steps. If reduced NAD is not reoxidised at the inner membrane, the NAD supply is used up and the cycle stops, even though oxygen is not used directly in it.
7. ATP is called the universal energy currency. What does 'universal' mean in this phrase?
A
it is the only molecule from which cells can release energy
B
it is made only in mitochondria in every type of cell
C
it is used to transfer energy in all known living organisms
D
it can pass from one organism to another in food chains
Show answer
Answer: C. All living cells, prokaryotic and eukaryotic, use ATP to transfer energy to the reactions that need it. Cells release energy from many substrates, and ATP is also made in the cytoplasm and in chloroplasts.
8. A respirometer contains germinating seeds and a small tube of potassium hydroxide solution, which absorbs carbon dioxide. The coloured liquid in the capillary tube moves towards the seeds. What does this movement measure?
A
the volume of carbon dioxide released by the seeds
B
the volume of oxygen taken in by the seeds
C
the difference between the carbon dioxide released and the oxygen taken in
D
the volume of water vapour absorbed by the seeds
Show answer
Answer: B. The potassium hydroxide removes carbon dioxide as it is released, so the fall in gas volume is due only to oxygen uptake. Without the potassium hydroxide, the movement shows the difference between the two gases.
9. Electron micrographs show that mitochondria in heart muscle have many more cristae than mitochondria in skin cells. What is the best explanation?
A
heart muscle respires anaerobically more, so it needs more glycolysis enzymes
B
heart muscle carries out more of the link reaction, which happens on the cristae
C
heart muscle needs more space in its mitochondria to store glycogen
D
heart muscle has a high demand for ATP, so a large area for oxidative phosphorylation is needed
Show answer
Answer: D. More cristae give more surface for electron transport chains and ATP synthase, matching the constant, high ATP demand of heart muscle. Glycolysis is in the cytoplasm and the link reaction in the matrix.
10. Which events occur during the link reaction?
A
pyruvate is reduced to an acetyl group, using reduced NAD produced during glycolysis
B
pyruvate is phosphorylated and split into two acetyl groups, which each join coenzyme A
C
pyruvate combines with oxaloacetate to form citrate, and coenzyme A is released again
D
pyruvate is decarboxylated and dehydrogenated, and the acetyl group joins coenzyme A
Show answer
Answer: D. Pyruvate (3C) loses carbon dioxide and hydrogen, which reduces NAD. The remaining 2C acetyl group combines with coenzyme A to form acetyl coenzyme A. Forming citrate is the first step of the Krebs cycle.
56, each with the answer and a short explanation, across 2 topics: Energy, Respiration. Every chapter test draws ten of them, so you can take it many times.
Is the A Level Biology (A2) chapter 1 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
