biology : class11 Anaerobic Nature : Location, Steps, Products, ATP Yield : Glycolysis MCQ Questions and Answers
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Anaerobic Nature
MCQ questions and answers.
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MCQ Questions
1. Why can glycolysis continue for a short period in a cell even when molecular oxygen is unavailable?
A.
Glycolysis directly uses oxygen to oxidize glucose
B.
NADH transfers electrons to pyruvate or its derivative, regenerating NAD+
C.
Oxygen is replaced by ATP as the final electron acceptor
D.
Mitochondria provide an alternative oxygen-independent respiratory chain
Correct Answer:
NADH transfers electrons to pyruvate or its derivative, regenerating NAD+
Explanation:
Glycolysis requires NAD+ during oxidation of glyceraldehyde-3-phosphate. Under anaerobic conditions, fermentation reoxidizes NADH to NAD+, allowing glycolysis to continue without molecular oxygen.
2. Under anaerobic conditions in skeletal muscle, which sequence most accurately describes the relationship between glycolysis and lactate formation?
A.
Glucose is converted directly into lactate, producing ATP only during lactate formation
B.
Pyruvate is reduced to lactate, and NADH is oxidized to NAD+
C.
Lactate is oxidized to pyruvate, while NAD+ is reduced to NADH
D.
Pyruvate enters the mitochondrion and is oxidized completely without oxygen
Correct Answer:
Pyruvate is reduced to lactate, and NADH is oxidized to NAD+
Explanation:
In anaerobic muscle metabolism, glycolysis produces pyruvate and NADH. Pyruvate accepts electrons from NADH to form lactate, regenerating NAD+ required for continued glycolysis.
3. Which statement best explains why anaerobic glycolysis cannot produce the same ATP yield as complete aerobic oxidation of one glucose molecule?
A.
Anaerobic glycolysis bypasses the ATP-generating steps of glycolysis
B.
Glucose is only partially oxidized to fermentation products, so much chemical energy remains unreleased
C.
Fermentation consumes all ATP formed during glycolysis
D.
The absence of oxygen prevents glucose from entering the cytoplasm
Correct Answer:
Glucose is only partially oxidized to fermentation products, so much chemical energy remains unreleased
Explanation:
Anaerobic metabolism stops at products such as lactate or ethanol, which still contain considerable energy. Therefore, only the net ATP formed directly in glycolysis is obtained.
4. A poison completely blocks the regeneration of NAD+ from NADH but does not inhibit the ATP-forming reactions of glycolysis directly. What is the most immediate consequence under anaerobic conditions?
A.
Glycolysis will accelerate indefinitely because NADH accumulates
B.
Glycolysis will soon stop because glyceraldehyde-3-phosphate oxidation requires NAD+
C.
Pyruvate will be completely oxidized using accumulated NADH
D.
The ATP investment phase will be skipped permanently
Correct Answer:
Glycolysis will soon stop because glyceraldehyde-3-phosphate oxidation requires NAD+
Explanation:
The oxidation of glyceraldehyde-3-phosphate requires NAD+ as an electron acceptor. If anaerobic pathways cannot regenerate NAD+, this step stops and glycolytic ATP production soon ceases.
5. In alcoholic fermentation by yeast, which overall change enables glycolysis to continue in the absence of oxygen?
A.
Glucose is converted to ethanol while NADH is oxidized to NAD+
B.
Pyruvate is converted to acetyl-CoA while NAD+ is reduced to NADH
C.
Ethanol is oxidized to glucose while ATP is converted to NAD+
D.
Carbon dioxide is reduced to pyruvate while NADH is produced
Correct Answer:
Glucose is converted to ethanol while NADH is oxidized to NAD+
Explanation:
In yeast, pyruvate is converted through acetaldehyde to ethanol. During this process, NADH is oxidized back to NAD+, maintaining the cofactor supply needed for anaerobic glycolysis.
6. If one molecule of glucose is metabolized anaerobically to lactate in a muscle cell, which combination correctly represents the net glycolytic outcome?
A.
2 lactate, 2 ATP, and oxidation of NADH to NAD+
B.
2 pyruvate, 4 ATP, and accumulation of NADH
C.
1 lactate, 2 ATP, and reduction of NAD+ to NADH
D.
2 acetyl-CoA, 2 ATP, and complete oxidation of NADH
Correct Answer:
2 lactate, 2 ATP, and oxidation of NADH to NAD+
Explanation:
Anaerobic glycolysis produces two pyruvate molecules, which are reduced to two lactate molecules. The net ATP gain is two molecules, while NADH is oxidized to regenerate NAD+.
7. Which observation most strongly supports the conclusion that fermentation is an anaerobic continuation of glycolysis rather than an independent pathway for glucose breakdown?
A.
Fermentation regenerates NAD+ and depends on pyruvate produced by glycolysis
B.
Fermentation produces more ATP than aerobic respiration
C.
Fermentation occurs only inside mitochondria
D.
Fermentation requires oxygen as the terminal electron acceptor
Correct Answer:
Fermentation regenerates NAD+ and depends on pyruvate produced by glycolysis
Explanation:
Fermentation uses glycolytic pyruvate and reoxidizes NADH to NAD+. Its principal role is to maintain NAD+ availability so the glycolytic sequence can continue without oxygen.
8. During oxygen deficiency, a plant cell converts pyruvate into ethanol and carbon dioxide. Which immediate biochemical purpose is served by this conversion?
A.
Generation of the majority of ATP from glucose
B.
Regeneration of NAD+ from NADH
C.
Formation of oxygen for the electron transport chain
D.
Conversion of ATP into glucose
Correct Answer:
Regeneration of NAD+ from NADH
Explanation:
Alcoholic fermentation under oxygen deficiency reoxidizes NADH to NAD+. This regenerated NAD+ permits the oxidation of glyceraldehyde-3-phosphate and sustains anaerobic glycolysis.
9. Which comparison between aerobic and anaerobic conditions is correct for glycolysis itself?
A.
The glycolytic reactions and direct net ATP yield are fundamentally the same, but the fate of pyruvate and NADH differs
B.
Glycolysis occurs only aerobically because oxygen is consumed in its first step
C.
Anaerobic glycolysis produces no pyruvate because pyruvate formation requires oxygen
D.
Aerobic glycolysis regenerates NAD+ by fermentation, whereas anaerobic glycolysis uses the electron transport chain
Correct Answer:
The glycolytic reactions and direct net ATP yield are fundamentally the same, but the fate of pyruvate and NADH differs
Explanation:
Glycolysis itself does not require oxygen and yields a net two ATP per glucose. In anaerobic conditions, fermentation handles pyruvate and regenerates NAD+, whereas aerobic cells can transfer reducing equivalents to oxygen-dependent pathways.
10. A microorganism produces ethanol and carbon dioxide from glucose only when oxygen is absent. If NAD+ regeneration is experimentally prevented, which result is most likely?
A.
Ethanol production and glycolytic flux will decline because NAD+ becomes limiting
B.
Ethanol production will increase because NADH cannot be consumed
C.
Glycolysis will yield unlimited ATP from the accumulated pyruvate
D.
Carbon dioxide will serve as the substitute electron acceptor and restore glycolysis
Correct Answer:
Ethanol production and glycolytic flux will decline because NAD+ becomes limiting
Explanation:
Anaerobic ethanol production is linked to NADH oxidation and NAD+ regeneration. Blocking this regeneration limits the NAD+ required for glyceraldehyde-3-phosphate oxidation, reducing glycolysis and ethanol formation.
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