Respiration in Plants — Class 11 MCQs with Answers
Class 11 CBSE Biology · Chapter 12
90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated
Practise the most important Class 11 CBSE Biology questions from Chapter 12, "Respiration in Plants". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that set top scorers in CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG apart.
To score well in "Respiration in Plants", focus on diagrams, key terms and knowing NCERT line by line. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This trains you to stay accurate under time pressure, as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Respiration in Plants, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 11 Biology mastery score. 14 sample questions are solved in full below, with the answer and a worked explanation. Sign in free to start practising.
Key concepts: Respiration in Plants (Class 11 Biology)
Cells release stored energy by oxidising food. This chapter follows glucose through glycolysis in the cytoplasm, the Krebs cycle in the mitochondrial matrix and the electron transport chain that drives ATP synthesis, contrasts these with fermentation, and uses respiratory quotient and amphibolic-pathway ideas to tie metabolism together.
- Glycolysis
- The EMP pathway in the cytoplasm splits one glucose into two pyruvate, giving a net 2 ATP and 2 NADH; it is common to all living organisms, aerobic or not.
- Fate of pyruvate
- Pyruvate may be oxidised aerobically in mitochondria, fermented to lactic acid, or fermented to ethanol and CO₂, depending on whether oxygen is available.
- Link reaction
- In the mitochondrial matrix pyruvate is decarboxylated and oxidised to acetyl-CoA, releasing one CO₂ and one NADH per pyruvate before the Krebs cycle.
- Krebs cycle
- Acetyl-CoA joins oxaloacetate to form citrate; each turn releases 2 CO₂ and yields 3 NADH, 1 FADH₂ and 1 GTP (equivalent to ATP).
Respiration in Plants — important questions & MCQs with answers (Class 11 Biology)
14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.
- Q1Easy
Glycolysis occurs in the:
A.Mitochondrial matrixB.Cytoplasm✓ CorrectC.NucleusD.ChloroplastAnswer: B. Cytoplasm
Explanation: Glycolysis is the one respiratory stage every living cell can run because it happens in the cytosol, needing no organelle — Krebs and the ETC instead need the mitochondrion, which is the mix-up tempting here.
- Q2Easy
Cellular respiration is best described as a process that:
A.Breaks C–C bonds to release energy as ATP✓ CorrectB.Synthesises glucose from CO₂C.Fixes nitrogenD.Splits water for O₂Answer: A. Breaks C–C bonds to release energy as ATP
Explanation: Cellular respiration oxidises the C–C and C–H bonds in food to release stored energy, trapped as ATP and reduced coenzymes — building glucose from CO₂ is photosynthesis, the reverse of this process.
- Q3Easy
Pyruvate dehydrogenase converts pyruvate to:
A.LactateB.Acetyl-CoA + CO₂ + NADH✓ CorrectC.EthanolD.OAAAnswer: B. Acetyl-CoA + CO₂ + NADH
Explanation: Pyruvate dehydrogenase, the mitochondrial link reaction, oxidatively decarboxylates pyruvate into acetyl-CoA, releasing CO₂ and reducing NAD⁺ — this bridges glycolysis to the Krebs cycle rather than feeding fermentation.
- Q4Easy
End product of glycolysis:
A.Pyruvate✓ CorrectB.GlucoseC.Acetyl-CoAD.CO₂Answer: A. Pyruvate
Explanation: Glycolysis splits one glucose into two 3-carbon pyruvate molecules, netting 2 ATP and 2 NADH — pyruvate, not acetyl-CoA, since that conversion needs the separate link reaction inside the mitochondrion.
- Q5Easy
The most common respiratory substrate in cells is:
A.Fructose onlyB.Glucose✓ CorrectC.Starch onlyD.CelluloseAnswer: B. Glucose
Explanation: Glucose is the default respiratory substrate glycolysis is built around; starch is hydrolysed to glucose units and fructose feeds into glycolytic intermediates, but cellulose's linkages resist ordinary cellular enzymes.
- Q6Easy
First substrate formed in Krebs cycle is:
A.Citrate✓ CorrectB.OAAC.SuccinateD.MalateAnswer: A. Citrate
Explanation: Citrate synthase joins 2-carbon acetyl-CoA to 4-carbon oxaloacetate to form 6-carbon citrate, the cycle's first product — oxaloacetate is instead the acceptor molecule regenerated at the cycle's end, not its starting product.
- Q7Medium
Krebs cycle takes place in:
A.RibosomeB.CytoplasmC.Outer membraneD.Mitochondrial matrix✓ CorrectAnswer: D. Mitochondrial matrix
Explanation: The Krebs (citric acid) cycle runs in the mitochondrial matrix, where its soluble enzymes access acetyl-CoA from the link reaction — the outer membrane and cytoplasm instead host earlier, unrelated steps.
- Q8Medium
Respiratory pathway is described as amphibolic because it:
A.Only synthesises ATPB.Is purely catabolicC.Involves both catabolism and anabolism✓ CorrectD.Only breaks down lipidsAnswer: C. Involves both catabolism and anabolism
Explanation: Respiration is amphibolic, not purely catabolic, because intermediates like acetyl-CoA and α-ketoglutarate double as starting points for synthesising fatty acids and amino acids, not just for being broken down for energy.
- Q9Medium
Net ATP yield from one glucose (aerobic, eukaryote):
A.~36-38✓ CorrectB.2C.100D.4Answer: A. ~36-38
Explanation: Complete aerobic oxidation of one glucose nets about 36-38 ATP: 2 from glycolysis, 2 from Krebs, and roughly 32-34 from the ETC — fermentation stops at just 2 ATP, the tempting low-number distractor.
- Q10Medium
Phosphorylation of glucose to glucose-6-phosphate is catalysed by:
A.AldolaseB.PhosphofructokinaseC.Pyruvate kinaseD.Hexokinase✓ CorrectAnswer: D. Hexokinase
Explanation: Hexokinase catalyses glycolysis's first, ATP-consuming step, phosphorylating glucose to glucose-6-phosphate — phosphofructokinase performs the analogous, rate-limiting phosphorylation one step later, on fructose-6-phosphate.
- Q11Medium
RQ for proteins is approximately:
A.1.0B.0.9✓ CorrectC.0.7D.0.0Answer: B. 0.9
Explanation: Proteins give an RQ of roughly 0.9, between carbohydrate's 1.0 and fat's 0.7, because their component amino acids are only partly oxidised already — an intermediate value, not a fixed round number like the others.
- Q12Hard
Fluoride inhibits glycolysis by blocking the enzyme:
A.Enolase✓ CorrectB.HexokinaseC.PFKD.Pyruvate kinaseAnswer: A. Enolase
Explanation: Fluoride combines with Mg²⁺ and phosphate to form a complex that specifically blocks enolase, the enzyme converting 2-phosphoglycerate to phosphoenolpyruvate — not the earlier hexokinase or PFK steps of glycolysis.
- Q13Hard
Photosynthesis and respiration are similar in that BOTH:
A.Produce O₂B.Involve electron transport chains and ATP synthesis by chemiosmosis✓ CorrectC.Reduce CO₂D.Occur only in green cellsAnswer: B. Involve electron transport chains and ATP synthesis by chemiosmosis
Explanation: Both photosynthesis and respiration run electron transport chains that pump protons and use the resulting gradient to drive ATP synthase — in chloroplast thylakoids for one, mitochondrial cristae for the other, not the same organelle.
- Q14Hard
Anaerobic fermentation in yeast yields:
A.Lactic acidB.Ethanol and CO₂✓ CorrectC.Acetic acidD.GlucoseAnswer: B. Ethanol and CO₂
Explanation: In anaerobic yeast, pyruvate from glycolysis is decarboxylated then reduced to ethanol and CO₂, regenerating NAD⁺ — muscle cells instead reduce pyruvate straight to lactic acid, releasing no CO₂ at all.
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Start this chapter free →Respiration in Plants — FAQs
What are the key concepts in Class 11 Biology Respiration in Plants?+
Cells release stored energy by oxidising food. This chapter follows glucose through glycolysis in the cytoplasm, the Krebs cycle in the mitochondrial matrix and the electron transport chain that drives ATP synthesis, contrasts these with fermentation, and uses respiratory quotient and amphibolic-pathway ideas to tie metabolism together. Key ideas include Glycolysis, Fate of pyruvate, Link reaction, Krebs cycle.
What does Class 11 Biology Chapter 12 (Respiration in Plants) cover on XamBaaz?+
It has 90 NCERT-based MCQs on "Respiration in Plants": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG.
Are these "Respiration in Plants" questions free to practise?+
Yes. Sign in with Google to practise "Respiration in Plants" free. Full unlimited access is ₹999/year on a launch offer until 1 December 2026. No chapter is charged separately.
How should I revise "Respiration in Plants" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Respiration in Plants" MCQs available with answers?+
Yes. 14 sample questions are shown here in full, each with the correct option and a step-by-step "Why" explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Respiration in Plants" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip, the same negative marking as NEET UG. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Respiration in Plants (Class 11 Biology)?+
The questions that matter most test Glycolysis, Fate of pyruvate, Link reaction, Krebs cycle. This page shows 14 solved important MCQs with answers and explanations; all 90 questions on the chapter are available as timed quizzes once you sign in.
Is there an online quiz for Respiration in Plants?+
Yes — Class 11 Biology Respiration in Plants has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.