Level 1 — RecognitionCellular Respiration

Cellular Respiration

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition

Time limit: 20 minutes Total marks: 30

Section A — Multiple Choice (1 mark each)

Choose the ONE best answer.

Q1. The overall equation for aerobic respiration is:

(a) $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$
(b) $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$
(c) $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
(d) $C_6H_{12}O_6 + 6H_2O \rightarrow 6CO_2 + 12H_2$

Q2. Glycolysis takes place in the:

(a) mitochondrial matrix
(b) inner mitochondrial membrane
(c) cytoplasm (cytosol)
(d) nucleus

Q3. The net ATP yield from glycolysis (per glucose) is:

(a) 2 ATP
(b) 4 ATP
(c) 36 ATP
(d) 38 ATP

Q4. During the link reaction (pyruvate oxidation), pyruvate is converted into:

(a) lactate
(b) acetyl-CoA
(c) ethanol
(d) citrate

Q5. The Krebs cycle occurs in the:

(a) cytoplasm
(b) mitochondrial matrix
(c) outer mitochondrial membrane
(d) ribosome

Q6. The final electron acceptor in the electron transport chain is:

(a) $NAD^+$
(b) carbon dioxide
(c) oxygen
(d) glucose

Q7. ATP synthase produces ATP using energy from:

(a) a proton (H⁺) gradient across the inner membrane
(b) direct oxidation of glucose
(c) breakdown of lactic acid
(d) sunlight

Q8. The product of lactic acid fermentation in human muscle is:

(a) ethanol and $CO_2$
(b) lactic acid (lactate)
(c) acetyl-CoA
(d) pyruvate and oxygen

Q9. Alcoholic fermentation in yeast produces:

(a) lactic acid only
(b) ethanol and carbon dioxide
(c) water and oxygen
(d) glucose

Q10. The main function of $NAD^+$ and $FAD$ in respiration is to act as:

(a) enzymes
(b) electron/hydrogen carriers
(c) structural proteins
(d) final electron acceptors

Section B — Matching (1 mark each, 5 marks)

Q11. Match each stage (i–v) to its correct location (A–E).

Stage		Location
(i) Glycolysis		A. Inner mitochondrial membrane
(ii) Link reaction		B. Cytoplasm
(iii) Krebs cycle		C. Mitochondrial matrix
(iv) Electron transport chain		D. Mitochondrial matrix
(v) Chemiosmosis (ATP synthase)		E. Inner mitochondrial membrane

(Write each location letter next to the stage number.)

Section C — True/False WITH Justification (2 marks each: 1 for T/F, 1 for reason)

Q12. Anaerobic respiration produces more ATP per glucose than aerobic respiration.

Q13. Oxygen is required for glycolysis to occur.

Q14. The link reaction releases carbon dioxide.

Q15. Chemiosmosis relies on a hydrogen ion (proton) gradient.

Q16. Fermentation regenerates $NAD^+$ so glycolysis can continue.

Q17. In aerobic respiration, most ATP is produced during glycolysis.

Q18. $FADH_2$ delivers its electrons to the electron transport chain at a later point than $NADH$ , so it yields slightly less ATP.

END OF PAPER

Answer keyMark scheme & solutions

Section A — MCQ (1 mark each)

Q1. (b) — Glucose reacts with oxygen to release $CO_2$ , water and energy. (1)

Q2. (c) — Glycolysis is anaerobic and occurs in the cytosol, not the mitochondrion. (1)

Q3. (a) — 4 ATP are produced but 2 are used to start the pathway, giving a net of 2 ATP. (1)

Q4. (b) — A 3-carbon pyruvate loses one carbon as $CO_2$ and combines with coenzyme A to form 2-carbon acetyl-CoA. (1)

Q5. (b) — The Krebs (citric acid) cycle enzymes are located in the mitochondrial matrix. (1)

Q6. (c) — Oxygen accepts electrons and $H^+$ at the end of the chain, forming water. (1)

Q7. (a) — Protons flow back through ATP synthase down their electrochemical gradient, driving ATP synthesis. (1)

Q8. (b) — Pyruvate is reduced to lactate, regenerating $NAD^+$ . (1)

Q9. (b) — Yeast converts pyruvate to ethanol and releases $CO_2$ . (1)

Q10. (b) — They pick up electrons/hydrogen (becoming $NADH$ / $FADH_2$ ) and deliver them to the ETC. (1)

Section B — Matching (Q11, 5 marks)

(i) Glycolysis → B (Cytoplasm) (1)
(ii) Link reaction → C or D (Mitochondrial matrix) (1)
(iii) Krebs cycle → C or D (Mitochondrial matrix) (1)
(iv) Electron transport chain → A or E (Inner mitochondrial membrane) (1)
(v) Chemiosmosis / ATP synthase → A or E (Inner mitochondrial membrane) (1)

Accept matrix answers C/D interchangeably and membrane answers A/E interchangeably since both refer to the same location.

Section C — True/False + Justification (2 marks each)

Q12. FALSE (1) — Aerobic respiration yields ~36–38 ATP per glucose; anaerobic (fermentation) yields only 2 ATP (from glycolysis). (1)

Q13. FALSE (1) — Glycolysis is anaerobic; it does not use oxygen and occurs whether oxygen is present or not. (1)

Q14. TRUE (1) — Each pyruvate is decarboxylated, releasing one $CO_2$ as it forms acetyl-CoA. (1)

Q15. TRUE (1) — The ETC pumps $H^+$ into the intermembrane space; the resulting proton gradient drives ATP synthase. (1)

Q16. TRUE (1) — Reducing pyruvate to lactate/ethanol reoxidises $NADH$ to $NAD^+$ , allowing glycolysis (which needs $NAD^+$ ) to keep producing ATP. (1)

Q17. FALSE (1) — Glycolysis nets only 2 ATP; most ATP (~32–34) is generated by oxidative phosphorylation at the ETC/chemiosmosis. (1)

Q18. TRUE (1) — $FADH_2$ feeds electrons in at complex II (further along), pumping fewer protons, so it yields ~1.5 ATP versus ~2.5 ATP for $NADH$ . (1)

[
  {"claim":"Net ATP from glycolysis is 2 (4 produced minus 2 invested)","code":"produced=4; invested=2; net=produced-invested; result = (net==2)"},
  {"claim":"Aerobic ATP yield (~36) exceeds anaerobic fermentation yield (2)","code":"aerobic=36; anaerobic=2; result = (aerobic > anaerobic)"},
  {"claim":"Total CO2 released per glucose in aerobic respiration is 6 (2 from link reaction + 4 from Krebs)","code":"link=2; krebs=4; total=link+krebs; result = (total==6)"},
  {"claim":"NADH yields more ATP than FADH2 in chemiosmosis (2.5 vs 1.5)","code":"nadh=Rational(5,2); fadh2=Rational(3,2); result = (nadh > fadh2)"}
]