Respiration in Plants — Class 11 MCQs with Answers

Respiration in Plants — important questions & MCQs with answers (Class 11 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Glycolysis occurs in the:

   AMitochondrial matrixBCytoplasmCNucleusDChloroplast
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   Answer: 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.

2. Q2 of 6Easy

   Cellular respiration is best described as a process that:

   ABreaks C–C bonds to release energy as ATPBSynthesises glucose from CO₂CFixes nitrogenDSplits water for O₂
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   Answer: 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.

3. Q3 of 6Medium

   Net ATP yield from one glucose (aerobic, eukaryote):

   A~36-38B2C100D4
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   Answer: ~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.

4. Q4 of 6Medium

   Krebs cycle takes place in:

   ARibosomeBCytoplasmCOuter membraneDMitochondrial matrix
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   Answer: 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.

5. Q5 of 6Hard

   Photosynthesis and respiration are similar in that BOTH:

   AProduce O₂BInvolve electron transport chains and ATP synthesis by chemiosmosisCReduce CO₂DOccur only in green cells
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   Answer: 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.

6. Q6 of 6Hard

   Anaerobic fermentation in yeast yields:

   ALactic acidBEthanol and CO₂CAcetic acidDGlucose
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   Answer: 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.

Respiration in Plants notes: key concepts (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).

Electron transport system

NADH and FADH₂ hand electrons to carriers on the inner membrane; the energy pumps protons, and O₂ is the final electron acceptor, forming water.

Oxidative phosphorylation

The proton gradient drives ATP synthase by chemiosmosis; each NADH yields about 3 ATP and each FADH₂ about 2 ATP during electron flow.

Net ATP yield

Complete aerobic oxidation of one glucose yields roughly 36–38 ATP, versus only a net 2 ATP from glycolysis alone under anaerobic conditions.

Fermentation

Anaerobic: yeast makes ethanol and CO₂ while muscle and bacteria make lactic acid, regenerating NAD⁺ but releasing under 7% of glucose's energy (2 ATP).

Respiratory quotient

RQ is CO₂ released divided by O₂ consumed; it is 1 for carbohydrates, below 1 for fats and proteins, and above 1 for organic acids.

Amphibolic pathway

Respiration is both catabolic and anabolic (amphibolic): intermediates are withdrawn to build fats, amino acids and other molecules, not just broken down.

Aerobic vs anaerobic

Aerobic respiration needs O₂ and fully oxidises glucose to CO₂ and water; anaerobic respiration partly breaks glucose down without O₂, yielding far less energy.

Respiratory substrates

Glucose is the preferred substrate, but fats, proteins and organic acids can also be respired, each shifting the RQ in a characteristic direction.