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Respiration in Plants — NEET MCQs with answers
Chapter 12 explains cellular respiration in plants — the breaking of C-C bonds of complex organic molecules by oxidation, releasing energy trapped as ATP, with glucose as the favoured substrate. It covers glycolysis in the cytoplasm, fermentation under anaerobic conditions, and aerobic respiration through the Krebs' cycle and the electron transport system in the mitochondria. It also discusses the amphibolic nature of the respiratory pathway and the respiratory quotient (RQ), which depends on the type of respiratory substrate.
Topics in this chapter
- 12.1 Do Plants Breathe?
- 12.2 Glycolysis
- 12.3 Fermentation
- 12.4 Aerobic Respiration
- 12.5 The Respiratory Balance Sheet
- 12.6 Amphibolic Pathway
- 12.7 Respiratory Quotient
Free practice questions
In fermentation, glucose undergoes:
- A. complete oxidation to CO2 and H2O
- B. no breakdown at all
- C. only a partial breakdown
- D. oxidation only in the mitochondria
Show answer
Answer: C — NCERT states that fermentation accounts for only a partial breakdown of glucose, whereas in aerobic respiration it is completely degraded.
NCERT Class 11 Biology Ch 12.5
Which of the following is NOT a step at which ATP is synthesised in glycolysis?
- A. BPGA to 3-phosphoglyceric acid
- B. PEP to pyruvic acid
- C. PGAL to BPGA
- D. None of these; all three yield ATP
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Answer: C — ATP is synthesised at the BPGA to PGA step and at the PEP to pyruvic acid step. The PGAL to BPGA conversion generates NADH, not ATP.
NCERT Class 11 Biology Ch 12.2
The metabolic pathway through which electrons pass from one carrier to another is called:
- A. Krebs' cycle
- B. Substrate level phosphorylation
- C. Glycolysis
- D. Electron transport system
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Answer: D — NCERT: 'The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system (ETS)'.
NCERT Class 11 Biology Ch 12.4
The term 'amphibolic' applied to the respiratory pathway means that the pathway
- A. Serves only breakdown reactions
- B. Serves only synthetic reactions
- C. Serves neither breakdown nor synthesis
- D. Serves both breakdown and synthesis
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Answer: D — NCERT derives the term from the fact that the pathway serves both catabolism (breakdown) and anabolism (synthesis). A pathway that does both is called amphibolic.
NCERT Class 11 Biology Ch 12.6
If a tissue respiring only on carbohydrate consumes 250 mL of O₂, the volume of CO₂ it evolves would be
- A. 125 mL
- B. 500 mL
- C. 250 mL
- D. 175 mL
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Answer: C — Completely oxidised carbohydrate has RQ = 1, i.e. CO₂ evolved = O₂ consumed. Hence 250 mL of O₂ consumed corresponds to 250 mL of CO₂ evolved.
NCERT Class 11 Biology Ch 12.7
In a non-green underground storage organ of a plant, respiration occurs using food that:
- A. Is obtained from dead and decaying matter
- B. Has been translocated from photosynthesising parts
- C. Is synthesised in situ by photosynthesis
- D. Is absorbed as glucose from the soil
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Answer: B — NCERT: non-green organs, tissues and cells need food for oxidation, so food has to be translocated to all non-green parts.
NCERT Class 11 Biology Ch 12.1
The substrate on which both pyruvic acid decarboxylase and lactate dehydrogenase act is:
- A. Pyruvic acid
- B. Glucose
- C. Acetyl CoA
- D. Lactic acid
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Answer: A — Both fermentation routes branch from pyruvic acid: yeast decarboxylates it, while muscle and some bacteria reduce it to lactic acid.
NCERT Class 11 Biology Ch 12.3
A calculation gives a net gain of 190 ATP. Assuming the NCERT balance sheet, the number of glucose molecules oxidised aerobically is:
- A. 6
- B. 5
- C. 4
- D. 10
Show answer
Answer: B — 190 / 38 = 5 glucose molecules.
NCERT Class 11 Biology Ch 12.5
During the conversion of PGAL to BPGA, the two redox equivalents removed from PGAL are in the form of:
- A. Two carbon dioxide molecules
- B. Two water molecules
- C. Two hydrogen atoms
- D. Two oxygen atoms
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Answer: C — NCERT states two redox-equivalents are removed 'in the form of two hydrogen atoms' from PGAL and transferred to a molecule of NAD+.
NCERT Class 11 Biology Ch 12.2
Of the eight NADH + H+ generated per glucose after glycolysis, how many arise from the citric acid cycle alone (i.e. excluding those from pyruvate oxidation)?
- A. 8
- B. 6
- C. 4
- D. 2
Show answer
Answer: B — Each pyruvate gives 1 NADH during oxidative decarboxylation, so 2 NADH come from that step. The citric acid cycle produces 3 NADH per turn and runs twice per glucose = 6 NADH. 2 + 6 = 8 in all.
NCERT Class 11 Biology Ch 12.4
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