101. How many ATP molecules are consumed during the preparatory phase of glycolysis?
ⓐ. Two ATP
ⓑ. Four ATP
ⓒ. One ATP
ⓓ. Three ATP
Correct Answer: Two ATP
Explanation: The preparatory phase of glycolysis requires an investment of energy to activate glucose for further breakdown. In this phase, two ATP molecules are consumed in phosphorylation steps. These early reactions help convert glucose into intermediates that can be split and processed further. Because of this ATP investment, the final energy gain of glycolysis is lower than the total ATP produced later. This is why the pathway is described as having an energy investment phase followed by an energy payoff phase. Thus two ATP molecules are consumed during the preparatory part of glycolysis.
102. Besides ATP and pyruvate, which reduced coenzyme is formed during glycolysis?
ⓐ. $FADH_2$
ⓑ. NADPH
ⓒ. NADH
ⓓ. Coenzyme A
Correct Answer: NADH
Explanation: During glycolysis, NAD is reduced and forms NADH as electrons and hydrogen are transferred during the oxidation of intermediate molecules. This makes NADH one of the important products of the pathway along with ATP and pyruvate. The reduced coenzyme stores reducing power that can be used in later metabolic processes. It is not the same as $FADH_2$, which is associated with later stages of respiration, or NADPH, which is more closely linked with biosynthetic pathways. Thus the reduced coenzyme generated in glycolysis is NADH. This is a key part of the energy yield of the pathway.
103. How many molecules of NADH are formed per molecule of glucose during glycolysis?
ⓐ. One
ⓑ. Four
ⓒ. Two
ⓓ. Three
Correct Answer: Two
Explanation: One molecule of glucose gives rise to two molecules of glyceraldehyde-3-phosphate during glycolysis, and each of these contributes to the formation of one NADH in the later part of the pathway. As a result, the total number of NADH molecules formed per glucose is two. This matches the fact that glycolysis processes two three-carbon units after the cleavage step. The reduced NADH molecules represent stored reducing power and are counted among the key products of the pathway. Their formation is one reason glycolysis is energetically important. Therefore the correct number of NADH molecules formed is two.
104. The ATP formed directly during glycolysis is produced mainly by:
ⓐ. oxidative phosphorylation
ⓑ. chemiosmosis
ⓒ. terminal oxidation
ⓓ. substrate-level phosphorylation
Correct Answer: substrate-level phosphorylation
Explanation: ATP in glycolysis is formed by substrate-level phosphorylation, which means that a phosphate group is directly transferred from a phosphorylated intermediate to ADP. This is different from oxidative phosphorylation, which occurs later in respiration through the electron transport system. Glycolysis takes place in the cytoplasm and does not depend on the mitochondrial electron transport chain for its ATP production. The pathway therefore provides ATP through direct chemical transfer steps. This mechanism explains how ATP can be produced even in the absence of oxygen. Hence the ATP generated in glycolysis arises mainly by substrate-level phosphorylation.
105. Which set correctly represents the main products obtained from one molecule of glucose at the end of glycolysis?
ⓐ. 2 pyruvate, 2 NADH, and net 2 ATP
ⓑ. 1 pyruvate, 4 NADH, and net 1 ATP
ⓒ. 2 acetyl-CoA, 2 $FADH_2$, and net 2 ATP
ⓓ. 6 carbon dioxide, 6 water, and 38 ATP
Correct Answer: 2 pyruvate, 2 NADH, and net 2 ATP
Explanation: At the end of glycolysis, one molecule of glucose yields two molecules of pyruvate, two molecules of NADH, and a net gain of two ATP molecules. These are the principal products used to summarize the pathway outcome. The glucose molecule is first split into two three-carbon units, which are then processed to pyruvate. During this process, ATP and NADH are also formed. This product pattern belongs specifically to glycolysis and should not be confused with the complete outputs of aerobic respiration. Therefore the correct set of major glycolytic products is 2 pyruvate, 2 NADH, and net 2 ATP.
106. What is the most important factor that determines the fate of pyruvate formed in glycolysis?
ⓐ. amount of chlorophyll in the cell
ⓑ. colour of the cytoplasm
ⓒ. thickness of the cell wall
ⓓ. availability of oxygen
Correct Answer: availability of oxygen
Explanation: The fate of pyruvate depends mainly on whether oxygen is available after glycolysis. If oxygen is present, pyruvate usually enters aerobic pathways for further oxidation. If oxygen is absent or insufficient, pyruvate is diverted into anaerobic pathways such as fermentation. This makes oxygen availability the key deciding condition for its next metabolic step. The structure or colour of the cell has no such direct control over pyruvate fate. Therefore the most important determining factor is the availability of oxygen.
107. Under aerobic conditions in eukaryotic cells, pyruvate formed in glycolysis is generally transported into the:
ⓐ. chloroplast
ⓑ. mitochondrion
ⓒ. vacuole
ⓓ. ribosome
Correct Answer: mitochondrion
Explanation: In eukaryotic cells, glycolysis occurs in the cytoplasm and produces pyruvate there. When oxygen is available, the pyruvate does not remain in the cytoplasm for fermentation but is transported into the mitochondrion for further aerobic breakdown. This transfer links glycolysis with the later stages of respiration. The mitochondrion is therefore the organelle that receives pyruvate under aerobic conditions. This movement is an important transition from cytoplasmic respiration to mitochondrial respiration. Hence pyruvate generally enters the mitochondrion when aerobic conditions prevail.
108. When oxygen is absent, pyruvate formed during glycolysis is most likely to:
ⓐ. remain permanently unchanged in the cytoplasm
ⓑ. enter the nucleus for ATP storage
ⓒ. undergo fermentation for further processing
ⓓ. convert directly into glucose without enzymes
Correct Answer: undergo fermentation for further processing
Explanation: In the absence of oxygen, pyruvate cannot continue through the normal aerobic route and is instead processed through fermentation. This allows the cell to maintain some metabolic activity even when oxygen is unavailable. Fermentation does not completely oxidize the substrate, but it provides a way for glycolysis-linked metabolism to continue under anaerobic conditions. The exact end products may differ in different organisms or tissues, but the general fate is fermentation. This makes fermentation the characteristic anaerobic continuation of glycolysis. Therefore pyruvate most likely undergoes fermentation when oxygen is absent.
109. If three glucose molecules undergo glycolysis completely, how many ATP molecules are formed in total before subtracting the ATP invested?
ⓐ. 3 ATP
ⓑ. 6 ATP
ⓒ. 12 ATP
ⓓ. 8 ATP
Correct Answer: 12 ATP
Explanation: One molecule of glucose yields a total of four ATP molecules during the energy-producing phase of glycolysis. The question asks for the gross ATP formed before subtracting the ATP used earlier, so the investment phase is not yet considered in the calculation. For three glucose molecules, this total is simply three times four. That gives twelve ATP molecules produced in all during glycolysis. This value represents the gross output, not the net gain. Therefore the correct total ATP formed before subtraction is 12 ATP.
110. If two glucose molecules complete glycolysis, what is the net ATP gain?
ⓐ. 4 ATP
ⓑ. 8 ATP
ⓒ. 2 ATP
ⓓ. 6 ATP
Correct Answer: 4 ATP
Explanation: The net gain of ATP from glycolysis is two ATP molecules per molecule of glucose. This net value is obtained after accounting for the ATP invested in the early preparatory phase and the ATP formed later in the pathway. When two glucose molecules undergo glycolysis, the net gain is doubled. Thus two glucose molecules yield four ATP molecules as the usable final gain from glycolysis itself. The question tests ATP accounting rather than gross production alone. Hence the correct net ATP gain is 4 ATP.
111. Which product of glycolysis represents stored reducing power rather than immediate ATP currency?
ⓐ. Pyruvate
ⓑ. Carbon dioxide
ⓒ. Glucose
ⓓ. NADH
Correct Answer: NADH
Explanation: NADH is formed during glycolysis when NAD accepts hydrogen and electrons during oxidation of an intermediate compound. This makes NADH a reduced coenzyme that stores reducing power rather than acting as the direct energy currency of the cell. ATP is the molecule used immediately for cellular work, whereas NADH mainly carries high-energy electrons for later metabolic use. Pyruvate is a carbon product of glycolysis, not a reduced coenzyme. Glucose is the starting substrate, not the reducing equivalent formed. Therefore NADH is the product that represents stored reducing power.
112. Assertion (A): The net ATP yield of glycolysis is lower than the total ATP formed during the pathway. Reason (R): Some ATP is consumed in the preparatory phase before later ATP-producing steps occur.
ⓐ. A is false, but R is true.
ⓑ. Both A and R are true, and R is the correct explanation of A.
ⓒ. Both A and R are true, but R is not the correct explanation of A.
ⓓ. A is true, but R is false.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: The assertion is correct because glycolysis forms more ATP in total than it finally contributes as net gain. The reason is also correct, since two ATP molecules are invested during the early phase of glycolysis to activate glucose and its intermediates. Later, ATP is produced, but the ATP already used must be subtracted to obtain the true net yield. This directly explains why gross ATP and net ATP are not the same. The relationship between the two statements is therefore logically sound. Hence both statements are true, and the reason correctly explains the assertion.
113. A plant cell has completed glycolysis and immediately uses one of its products for active transport across a membrane. Which product is being used directly?
ⓐ. ATP
ⓑ. Pyruvate
ⓒ. NADH
ⓓ. Oxygen
Correct Answer: ATP
Explanation: Active transport requires immediate usable energy, and ATP serves as the direct energy currency for such cellular work. Glycolysis produces ATP in the cytoplasm, and this ATP can be used directly by the cell without waiting for pyruvate to enter later respiratory stages. NADH carries reducing power but is not the usual immediate phosphate-energy currency for membrane transport. Pyruvate is mainly an intermediate whose later fate depends on metabolic conditions. Oxygen is not a product of glycolysis at all. Therefore ATP is the product used directly for active transport.
114. Which statement best corrects the misconception that pyruvate is the final end of respiration?
ⓐ. Pyruvate is a waste product that has no later metabolic role
ⓑ. Pyruvate is formed only when oxygen is absent
ⓒ. Pyruvate is the end product of glycolysis but a starting point for later respiratory pathways
ⓓ. Pyruvate is always stored permanently in the cytoplasm after glycolysis
Correct Answer: Pyruvate is the end product of glycolysis but a starting point for later respiratory pathways
Explanation: Pyruvate is correctly described as the final product of glycolysis, but that does not mean respiration ends there. It is actually an important intermediate from which later pathways continue depending on oxygen availability and cellular conditions. Under aerobic conditions, it undergoes further oxidation, while under anaerobic conditions it is diverted into fermentation-related routes. This makes pyruvate a transition point rather than a useless end product. The idea is important because students often confuse the end of glycolysis with the end of all respiration. Therefore pyruvate is the end product of glycolysis but a starting point for later pathways.
115. Under both aerobic and anaerobic conditions, which outcome of glycolysis is certainly common before the later fate of pyruvate becomes different?
ⓐ. Direct formation of acetyl-CoA
ⓑ. Release of large amounts of carbon dioxide
ⓒ. Complete oxidation of glucose to water
ⓓ. Formation of pyruvate with net ATP and NADH
Correct Answer: Formation of pyruvate with net ATP and NADH
Explanation: Glycolysis is the common initial stage of respiration and occurs before the pathway branches according to oxygen availability. Whether the cell later follows aerobic respiration or an anaerobic route, glycolysis first produces pyruvate, a net gain of ATP, and NADH. These outcomes are therefore common to both conditions. The difference arises only afterward, when pyruvate follows different metabolic fates. The pathway does not directly form acetyl-CoA under all conditions, nor does glycolysis itself completely oxidize glucose. Hence the common outcome is the formation of pyruvate along with net ATP and NADH.
116. Which comparison between ATP and NADH formed in glycolysis is correct?
ⓐ. ATP stores reducing equivalents, whereas NADH is used only for membrane transport
ⓑ. ATP is the immediate energy currency, whereas NADH carries reducing equivalents for later use
ⓒ. ATP and NADH are identical in role because both are direct end products of fermentation
ⓓ. ATP is formed only in the mitochondrion, whereas NADH is absent from glycolysis
Correct Answer: ATP is the immediate energy currency, whereas NADH carries reducing equivalents for later use
Explanation: ATP and NADH are both important products of glycolysis, but they do not play the same role. ATP is the molecule used directly by the cell for immediate energy-requiring work such as transport, synthesis, and movement at the cellular level. NADH, on the other hand, acts as a reduced coenzyme that carries electrons and hydrogen for later metabolic use. This distinction helps students separate direct energy currency from stored reducing power. Glycolysis forms both, but their functions are different. Therefore ATP is the immediate energy currency, while NADH carries reducing equivalents for later use.
117. What is fermentation in the context of respiration?
ⓐ. A complete oxidation of glucose in the presence of oxygen
ⓑ. An anaerobic breakdown of pyruvate with limited energy release
ⓒ. A process in which carbon dioxide is fixed into glucose
ⓓ. A pathway that occurs only inside mitochondria
Correct Answer: An anaerobic breakdown of pyruvate with limited energy release
Explanation: Fermentation is a type of anaerobic respiration in which pyruvate formed after glycolysis is further processed without the use of oxygen. It allows the cell to continue releasing a small amount of energy when oxygen is absent or insufficient. The breakdown in fermentation is incomplete, so the energy yield is much less than in aerobic respiration. It is therefore considered an alternative pathway rather than the main high-energy route. Fermentation is closely associated with the continuation of glycolysis under anaerobic conditions. Thus it is best defined as anaerobic processing of pyruvate with limited energy release.
118. Which are the main end products of alcoholic fermentation?
ⓐ. Lactic acid and oxygen
ⓑ. Ethanol and carbon dioxide
ⓒ. Pyruvate and water
ⓓ. Acetyl-CoA and carbon dioxide
Correct Answer: Ethanol and carbon dioxide
Explanation: In alcoholic fermentation, pyruvate is ultimately converted into ethanol, and carbon dioxide is released during the process. This pathway is characteristic of certain microorganisms such as yeast. The formation of ethanol and carbon dioxide distinguishes alcoholic fermentation clearly from lactic acid fermentation. The products show that the substrate is not completely oxidized, which is why the energy yield remains low. These end products are the central identifying feature of alcoholic fermentation. Therefore ethanol and carbon dioxide are the correct products.
119. Alcoholic fermentation commonly occurs in:
ⓐ. yeast cells
ⓑ. guard cells of leaves
ⓒ. xylem vessels
ⓓ. root cap only
Correct Answer: yeast cells
Explanation: Yeast is the classic organism associated with alcoholic fermentation. Under anaerobic conditions, yeast cells convert pyruvate into ethanol and carbon dioxide after glycolysis. This ability is widely used in baking and brewing, which makes yeast an especially important biological example of fermentation. The question focuses on the organism most commonly cited for this pathway. While fermentation is a biochemical pathway, its association with yeast is fundamental to its understanding. Thus yeast cells commonly carry out alcoholic fermentation.
120. What is the principal end product of lactic acid fermentation?
ⓐ. Ethanol
ⓑ. Pyruvate
ⓒ. Carbon dioxide
ⓓ. Lactic acid
Correct Answer: Lactic acid
Explanation: In lactic acid fermentation, pyruvate is reduced to lactic acid under anaerobic conditions. This pathway differs from alcoholic fermentation because it does not end in ethanol. The formation of lactic acid is the key identifying feature of this type of fermentation. It is important because it allows glycolysis to continue in conditions where oxygen is not adequately available. The process therefore serves as an anaerobic alternative for continued metabolism. Hence lactic acid is the principal product of lactic acid fermentation.
