Fermentation (Anaerobic) — NEET Biology MCQs with Solutions
Free NEET Biology Fermentation (Anaerobic) MCQs with step-by-step solutions (35 questions). Part of Respiration in Plants. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Fermentation (Anaerobic) · easy · theory
In yeast, anaerobic respiration (fermentation) converts pyruvate to:
A. Water
B. Ethanol and CO₂ ✓ Correct
C. Lactic acid
D. Acetyl CoA
Solution: Yeast performs alcoholic fermentation: pyruvate → acetaldehyde → ethanol + CO₂.
Q2 — Fermentation (Anaerobic) · easy · theory
In our muscle cells during vigorous exercise, pyruvate is converted to ______ under low oxygen:
A. CO₂ and water
B. Glucose
C. Ethanol
D. Lactic acid ✓ Correct
Solution: Lack of O₂ forces lactic acid fermentation in muscles, regenerating NAD⁺ for glycolysis.
Q3 — Fermentation (Anaerobic) · medium · theory
The purpose of fermentation (reducing pyruvate) is to:
A. Fix carbon dioxide
B. Regenerate NAD⁺ so that glycolysis can continue ✓ Correct
C. Produce large amounts of ATP
D. Synthesise glucose
Solution: Fermentation reoxidises NADH back to NAD⁺, allowing glycolysis to keep making its small ATP yield without O₂.
Q4 — Fermentation (Anaerobic) · medium · theory
The net ATP yield per glucose in fermentation is only ______, because:
A. 4 ATP; ETS runs
B. 38 ATP; O₂ is used
C. 2 ATP; glucose is only partially oxidised ✓ Correct
D. 36 ATP; glucose is fully oxidised
Solution: Without the Krebs cycle and ETS, only the 2 ATP of glycolysis are gained — glucose is not fully broken down.
Q5 — Fermentation (Anaerobic) · hard · theory
Both alcoholic and lactic acid fermentation are hazardous because:
A. They produce too much ATP
B. Less than 7% of the energy in glucose is released and not all of it is trapped as ATP ✓ Correct
C. They consume oxygen
D. They release only water
Solution: Fermentation is energetically inefficient (only ~2 ATP) and yields incompletely oxidised, sometimes toxic, products.
Q6 — Fermentation (Anaerobic) · hard · theory
The enzyme pyruvic acid decarboxylase and alcohol dehydrogenase are required in ______ fermentation:
A. Alcoholic (yeast) ✓ Correct
B. Photorespiratory
C. Lactic acid
D. Aerobic
Solution: Alcoholic fermentation needs pyruvate decarboxylase (→ acetaldehyde) and alcohol dehydrogenase (→ ethanol).
Q7 — Fermentation (Anaerobic) · easy · numerical
Alcoholic fermentation in yeast converts pyruvate to ethanol in two enzymatic steps. Which pair of enzymes carries this out, in order?
A. Alcohol dehydrogenase, then pyruvate decarboxylase
B. Pyruvate dehydrogenase, then alcohol dehydrogenase
C. Lactate dehydrogenase, then pyruvate decarboxylase
D. Pyruvate decarboxylase, then alcohol dehydrogenase ✓ Correct
Solution: Pyruvate decarboxylase removes CO₂ from pyruvate to give acetaldehyde, then alcohol dehydrogenase reduces acetaldehyde to ethanol using NADH, regenerating NAD⁺.
Q8 — Fermentation (Anaerobic) · easy · numerical
Which of the following distinguishes alcoholic fermentation from lactic acid fermentation?
A. CO₂ is released in alcoholic fermentation but not in lactic acid fermentation ✓ Correct
B. ATP is produced in lactic acid fermentation but not in alcoholic fermentation
C. NADH is oxidised in alcoholic fermentation but reduced in lactic acid fermentation
D. Oxygen is required for alcoholic fermentation but not for lactic acid fermentation
Solution: Alcoholic fermentation decarboxylates pyruvate, releasing CO₂ before producing ethanol; lactic acid fermentation reduces pyruvate directly to lactate with no CO₂ release. Both are anaerobic and regenerate NAD⁺.
Q9 — Fermentation (Anaerobic) · easy · numerical
Both lactic acid and alcoholic fermentation yield less than 7% of the energy available in glucose and do not release all of it. Which statement correctly explains this?
A. Fermentation destroys the NADH so no energy can be captured
B. The end products (lactic acid or ethanol) still contain most of the chemical energy of glucose ✓ Correct
C. Fermentation converts glucose entirely to CO₂ and water
D. All the energy of glucose is lost as heat during fermentation
Solution: Fermentation stops at lactate or ethanol, both energy-rich molecules; only the net 2 ATP of glycolysis are captured, so less than 7% of glucose energy is released.
Q10 — Fermentation (Anaerobic) · easy · numerical
During strenuous exercise, when muscle cells run short of oxygen, the immediate benefit of converting pyruvate to lactate is that it:
A. Reoxidises NADH to NAD⁺ so that glycolysis can keep producing ATP ✓ Correct
B. Generates additional ATP directly from lactate
C. Produces oxygen needed for the electron transport system
D. Releases CO₂ that stimulates faster breathing
Solution: Lactate dehydrogenase transfers electrons from NADH to pyruvate, regenerating NAD⁺. This keeps glycolysis (and its ATP output) running when oxygen is scarce, even though no extra ATP comes from the reduction itself.
Q11 — Fermentation (Anaerobic) · medium · numerical
A brewer notices vigorous bubbling in a fermenting yeast vat. Which two products of alcoholic fermentation are responsible for this observation and the eventual alcohol content?
A. Oxygen (the bubbles) and lactic acid (the alcohol)
B. Hydrogen gas (the bubbles) and ethanol (the alcohol)
C. Carbon dioxide (the bubbles) and lactic acid (the alcohol)
D. Carbon dioxide (the bubbles) and ethanol (the alcohol) ✓ Correct
Solution: Yeast decarboxylates pyruvate, releasing CO₂ (the visible bubbles), and reduces the resulting acetaldehyde to ethanol — the alcohol that accumulates.
Q12 — Fermentation (Anaerobic) · medium · numerical
Assertion (A): Yeasts poison themselves to death during fermentation. Reason (R): The accumulation of ethanol beyond a certain concentration becomes toxic to the yeast cells.
A. A is false but R is true
B. Both A and R are true but R is not the correct explanation of A
C. A is true but R is false
D. Both A and R are true and R is the correct explanation of A ✓ Correct
Solution: In distilleries yeasts continue fermenting until the ethanol they produce accumulates to a level that is toxic to them, which is why fermentation-derived alcohol cannot exceed roughly 13%.
Q13 — Fermentation (Anaerobic) · medium · numerical
A microbiologist tracks the fate of the two NADH molecules made in glycolysis under strictly anaerobic conditions in yeast. What happens to them?
A. They are used to reduce pyruvate directly to lactate
B. They are reoxidised to NAD⁺ as acetaldehyde is reduced to ethanol ✓ Correct
C. They pass their electrons to oxygen via the ETS to make ATP
D. They accumulate unchanged because there is no way to reoxidise them
Solution: In yeast the glycolytic NADH is reoxidised when alcohol dehydrogenase reduces acetaldehyde to ethanol; there is no oxygen and no ETS involvement in anaerobic yeast.
Q14 — Fermentation (Anaerobic) · medium · numerical
Which statement about the ATP economics of fermentation compared with aerobic respiration is correct?
A. Fermentation nets 36–38 ATP per glucose, similar to aerobic respiration
B. Fermentation nets only 2 ATP per glucose, far fewer than aerobic respiration, because pyruvate is not fully oxidised ✓ Correct
C. Fermentation produces ATP only during the reduction of pyruvate
D. Fermentation produces more ATP than aerobic respiration because it is faster
Solution: All fermentation ATP comes from glycolysis (net 2). The reduction of pyruvate merely recycles NAD⁺ and yields no ATP, so fermentation is far less efficient than aerobic respiration.
Q15 — Fermentation (Anaerobic) · medium · numerical
Certain bacteria, our muscle cells, and some fungi and plants can respire anaerobically. Which grouping correctly pairs the organism/tissue with its principal fermentation product?
A. Human muscle → lactic acid; yeast → ethanol + CO₂ ✓ Correct
B. Human muscle → CO₂ + water; yeast → lactic acid
C. Human muscle → ethanol; yeast → lactic acid
D. Human muscle → ethanol + CO₂; yeast → lactic acid
Solution: Skeletal muscle performs lactic acid fermentation, whereas yeast performs alcoholic fermentation producing ethanol and CO₂.
Q16 — Fermentation (Anaerobic) · medium · numerical
In lactic acid fermentation, how many carbon atoms does the end product (lactate) contain, and how does this compare with the substrate pyruvate?
A. Two carbons — one less than pyruvate, because CO₂ is released
B. Six carbons — twice pyruvate, since two pyruvates combine
C. Four carbons — one more than pyruvate, because CO₂ is added
D. Three carbons — the same as pyruvate, since no CO₂ is lost ✓ Correct
Solution: Lactic acid fermentation simply reduces the three-carbon pyruvate to three-carbon lactate; no decarboxylation occurs, so no carbon is lost (unlike alcoholic fermentation).
Q17 — Fermentation (Anaerobic) · medium · theory
How many statements are correct about fermentation? i. Very low energy is released, < 7% of the energy in glucose. ii. In animal cells, when oxygen is inadequate, acetic acid is formed during respiration. iii. It can be dangerous as it leads to acid and alcohol formation.
A. 3
B. 2 ✓ Correct
C. 1
D. 0
Solution: Statements i and iii are correct; ii is wrong because lactic acid (not acetic acid) is formed in animal cells under low oxygen.
Q18 — Fermentation (Anaerobic) · easy · theory
Yeasts poison themselves to death during alcoholic fermentation when the concentration of alcohol reaches about
A. 12%
B. 15%
C. 13% ✓ Correct
D. 17%
Solution: NCERT states yeasts poison themselves to death when alcohol concentration reaches about 13 per cent.
Q19 — Fermentation (Anaerobic) · easy · theory
Fermentation occurs when there is
A. No supply of water
B. Complete supply of oxygen
C. Complete supply of water
D. No supply of oxygen ✓ Correct
Solution: Fermentation is anaerobic, occurring in the absence of oxygen.
Q20 — Fermentation (Anaerobic) · medium · theory
In alcoholic fermentation, pyruvate is converted to which among the following?
A. CO2 and carboxylic acid
B. CO2 and methanol
C. Ethanol, CO2 and NADH is reoxidised ✓ Correct
D. CO2 and ethanol only
Solution: Pyruvate is converted to ethanol and CO2, with NADH being reoxidised to NAD+ in the process.
Q21 — Fermentation (Anaerobic) · medium · theory
Which enzyme(s) are responsible for alcoholic fermentation?
A. Both pyruvic acid decarboxylase and alcohol dehydrogenase ✓ Correct
B. Only pyruvic acid decarboxylase
C. Only alcohol dehydrogenase
D. Lactate dehydrogenase
Solution: Alcoholic fermentation involves both pyruvic acid decarboxylase and alcohol dehydrogenase.
Q22 — Fermentation (Anaerobic) · easy · theory
Which enzyme is involved in lactic acid fermentation?
A. Aldolase
B. Lactate dehydrogenase ✓ Correct
C. Pyruvic acid decarboxylase
D. Alcohol dehydrogenase
Solution: Lactate dehydrogenase converts pyruvate to lactic acid in lactic acid fermentation.
Q23 — Fermentation (Anaerobic) · medium · theory
Choose the correct option about the fermentation process: i. Oxidation of ADP to ATP takes place. ii. Reduction of ATP to ADP takes place. iii. Reducing agent NADH + H+ is reoxidised to NAD+. iv. Formation of NADH + H+ takes place by oxidation.
A. Only iii ✓ Correct
B. ii and iii
C. ii and iv
D. Both i and iii
Solution: In fermentation NADH + H+ is reoxidised to NAD+; the other statements are incorrect.
Q24 — Fermentation (Anaerobic) · medium · theory
Assertion (A): Anaerobic respiration in plants produces ethanol and CO2. Reason (R): It occurs in the absence of oxygen in the cytoplasm.
A. A false, R true
B. Both true, R does not explain A ✓ Correct
C. A true, R false
D. Both true, R explains A
Solution: Both are correct, but the anaerobic cytoplasmic condition does not directly explain the specific end products.
Q25 — Fermentation (Anaerobic) · medium · theory
Assertion (A): Fermentation yields only 2 ATP. Reason (R): Glucose is incompletely oxidized to pyruvate or ethanol.
A. A true, R false
B. Both true, R explains A ✓ Correct
C. A false, R true
D. Both true, R does not explain A
Solution: Incomplete oxidation leaves most energy locked in the products, explaining the low 2 ATP yield.
Q26 — Fermentation (Anaerobic) · medium · theory
Assertion (A): In waterlogged conditions, plants switch to anaerobic respiration. Reason (R): Roots lack oxygen supply.
A. Both true, R does not explain A
B. Both true, R explains A ✓ Correct
C. A true, R false
D. A false, R true
Solution: Oxygen deprivation of roots in waterlogged soil forces the switch to anaerobic respiration, so R explains A.
Q27 — Fermentation (Anaerobic) · medium · theory
Assertion (A): Anaerobic respiration is less efficient. Reason (R): The net gain is only 2 ATP versus about 36 in aerobic respiration.
A. Both true, R does not explain A
B. A false, R true
C. A true, R false
D. Both true, R explains A ✓ Correct
Solution: The far lower ATP yield (2 vs 36) is exactly why anaerobic respiration is less efficient, so R explains A.
Q28 — Fermentation (Anaerobic) · medium · theory
Statement I: Fermentation in yeast produces ethanol but no CO2. Statement II: Fermentation occurs in both prokaryotes and eukaryotes.
A. Statement I is incorrect but Statement II is correct ✓ Correct
B. Statement I is correct but Statement II is incorrect
C. Both Statement I and Statement II are incorrect
D. Both Statement I and Statement II are correct
Solution: Alcoholic fermentation produces both ethanol and CO2 (I incorrect), and fermentation does occur in prokaryotes and eukaryotes (II correct).
Q29 — Fermentation (Anaerobic) · medium · theory
Statement I: Pyruvate is decarboxylated to acetyl CoA under anaerobic conditions. Statement II: Under anaerobic conditions, pyruvate forms lactate in plants.
A. Both Statement I and Statement II are correct
B. Statement I is correct but Statement II is incorrect
C. Both Statement I and Statement II are incorrect ✓ Correct
D. Statement I is incorrect but Statement II is correct
Solution: Pyruvate to acetyl CoA is an aerobic step (I incorrect), and plants form ethanol, not lactate, anaerobically (II incorrect).
Q30 — Fermentation (Anaerobic) · medium · theory
Statement I: In alcoholic fermentation, pyruvic acid is converted to lactic acid and CO2. Statement II: Aldolase catalyses this reaction in yeast.
A. Both Statement I and Statement II are incorrect ✓ Correct
B. Statement I is correct but Statement II is incorrect
C. Statement I is incorrect but Statement II is correct
D. Both Statement I and Statement II are correct
Solution: Alcoholic fermentation gives ethanol and CO2, not lactic acid (I incorrect), and is catalysed by pyruvate decarboxylase and alcohol dehydrogenase, not aldolase (II incorrect).