Bioenergetics

Bioenergetics MDCAT MCQs with answers

54 past paper MCQs from Biology unit 2, Bioenergetics, across 1 topic. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Respiration

1.What is the end product of glucose breakdown by yeast in anaerobic respiration? (MDCAT 2022)

  1. ethanol and oxygen
  2. ethanol and water
  3. ethanol and $\mathrm{CO_2}$
  4. lactic acid and $\mathrm{CO_2}$
Show answer

Correct answer: (c) ethanol and $\mathrm{CO_2}$

Yeast ferments sugar to ethanol and carbon dioxide.

2.Each carrier in the electron transport chain is first ______ and then ______. (MDCAT 2022)

  1. broken down, regenerated
  2. generated, broken down
  3. oxidized, reduced
  4. reduced, oxidized
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Correct answer: (d) reduced, oxidized

A carrier takes electrons from the one before it, which reduces it, and passes them on, which oxidizes it again.

3.The electron transport chain explains: (MDCAT 2022)

  1. photophosphorylation
  2. the Z-scheme
  3. photolysis
  4. the mechanism of ATP synthesis
Show answer

Correct answer: (d) the mechanism of ATP synthesis

The energy released as electrons fall down the chain is what pumps protons and drives ATP synthase.

4.Which of the following is NOT a consequence of anaerobic respiration in human muscle cells? (MDCAT 2022)

  1. cramps
  2. high consumption of energy
  3. pain
  4. tiredness
Show answer

Correct answer: (b) high consumption of energy

Anaerobic respiration yields far less energy per glucose, not more; the lactic acid it leaves behind causes the rest.

5.The most primitive respiratory process occurring in a living cell is; (UHS MDCAT 2025)

  1. Lactic acid fermentation
  2. Alcoholic fermentation
  3. Glycolysis
  4. Krebs's cycle
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Correct answer: (c) Glycolysis

Glycolysis needs no oxygen and no organelle, and every kind of cell still uses it.

6.Living cells Do NOT directly acquire energy released from the breakdown of food molecules because: (KMU MDCAT 2025)

  1. Glucose cannot be broken down inside the cells
  2. Energy released is too small to be used by the cells
  3. Glucose molecules do not store any energy
  4. The energy released is too large, leading to heating and wastage
Show answer

Correct answer: (d) The energy released is too large, leading to heating and wastage

Oxidizing the whole molecule at once would waste the energy as heat, so it is released in small steps into ATP.

7.In glycolysis glucose is: (NUMS MDCAT 2025)

  1. Oxidized into pyruvic acid
  2. Reduced into pyruvate
  3. Broken down to G3P
  4. Reduced to NADPH
Show answer

Correct answer: (a) Oxidized into pyruvic acid

Glycolysis oxidizes glucose to two molecules of pyruvic acid and gives up hydrogen to NAD.

8.In the following process the cells release energy from oxidation of food molecules? (SIBA MDCAT 2025)

  1. Cellular respiration
  2. Photosynthesis
  3. DNA replication
  4. Protein synthesis
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Correct answer: (a) Cellular respiration

Cellular respiration is the controlled oxidation of food to release energy as ATP.

9.How many NADH are produced, when one Acetyl co-A is oxidized during Krebs's cycle? (SIBA MDCAT 2025)

  1. 1
  2. 2
  3. 3
  4. 6
Show answer

Correct answer: (c) 3

One turn of the cycle yields three NADH, one FADH2 and one GTP.

10.How many ATPs are produced during oxidative phase of glycolysis? (SZABMU MDCAT 2025)

  1. 2
  2. 4
  3. 34
  4. 36
Show answer

Correct answer: (b) 4

The payoff phase makes four ATP, of which two repay the investment of the first phase.

11.The process of ATP synthesis through a combination of electrochemical and osmotic events is known as: (KMU MDCAT 2024)

  1. Fermentation
  2. Glycolysis
  3. Oxidative phosphorylation
  4. Oxidation of pyruvate to acetyl CoA
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Correct answer: (c) Oxidative phosphorylation

Electrons passed down the chain pump protons, and their return through ATP synthase makes the ATP.

12.During glycolysis, isomerization takes place in the formation of: (NUMS MDCAT 2024)

  1. Dihydroxyacetone phosphate and 2-phosphoglycerate
  2. G3P and fructose 6-phosphate
  3. PEP and pyruvate
  4. Fructose 6-phosphate and 3-phosphoglycerate
Show answer

Correct answer: (b) G3P and fructose 6-phosphate

Glucose 6-phosphate is isomerized to fructose 6-phosphate, and dihydroxyacetone phosphate to G3P.

13.Fats and proteins are metabolized via — which of the following serves as common duct for both metabolisms? (NUMS MDCAT 2024)

  1. Acetyl-CoA
  2. Pyruvate
  3. G3P
  4. Lactate
Show answer

Correct answer: (a) Acetyl-CoA

Fatty acids and most amino acids are cut down to acetyl coenzyme A before entering the Krebs cycle.

14.What is the end product of glucose by yeast in anaerobic respiration? (UHS MDCAT 2023)

  1. Ethanol and oxygen
  2. Ethanol and water
  3. Ethanol and CO2
  4. Lactic acid and CO2
Show answer

Correct answer: (c) Ethanol and CO2

Yeast ferments glucose to ethanol and carbon dioxide.

15.Each carrier in Electron Transport Chain is first ______ and then ______. (UHS MDCAT 2023)

  1. Broken-down, Regenerate
  2. Generated, Broken-down
  3. Oxidized, Reduced
  4. Reduced, Oxidized
Show answer

Correct answer: (d) Reduced, Oxidized

Each carrier takes the electrons from the one before, so it is reduced, then passes them on and is oxidized again.

16.Electron transport chain explains: (UHS MDCAT 2023)

  1. Photophosphorylation
  2. Z-Scheme
  3. Photolysis
  4. Mechanism of ATP synthesis
Show answer

Correct answer: (d) Mechanism of ATP synthesis

The chain pumps protons whose return through ATP synthase makes the ATP.

17.Which of the following is NOT a consequence of anaerobic respiration in humans muscles cells? (UHS MDCAT 2023)

  1. Cramps
  2. High consumption of energy
  3. Pain
  4. Tiredness
Show answer

Correct answer: (b) High consumption of energy

Anaerobic respiration yields far less energy, not more; the cramps and pain come from the lactic acid.

18.Which of the following is used in baking? (UHS MDCAT 2023)

  1. Aerobic respiration
  2. Anaerobic respiration
  3. External respiration
  4. Internal respiration
Show answer

Correct answer: (b) Anaerobic respiration

The yeast in dough ferments anaerobically, and the carbon dioxide raises the bread.

19.Which is the major event in electron transport chain? (UHS MDCAT 2023)

  1. ATP synthesis
  2. Substitution
  3. Decarboxylation
  4. Isomerisation
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Correct answer: (a) ATP synthesis

The chain pumps protons whose return through ATP synthase makes most of the cell’s ATP.

20.Metabolism is about _____. (PMC MDCAT 2022)

  1. All chemical reactions taking place in a cell
  2. All chemical reactions in prokaryotic bodies
  3. All chemical reactions In eukaryotic bodies
  4. All chemical reactions in an industry
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Correct answer: (a) All chemical reactions taking place in a cell

Metabolism is the whole of the chemical change going on in a cell.

21.The end products of aerobic respiration are: (PMC MDCAT 2022)

  1. Sugar and oxygen
  2. Water and energy
  3. Carbon dioxide, water, and energy
  4. Carbon dioxide and energy
Show answer

Correct answer: (c) Carbon dioxide, water, and energy

Aerobic respiration ends in carbon dioxide, water and ATP.

22.The prime function of ATP is to: (PMC MDCAT 2022)

  1. Act as a catalyst
  2. describe the function of a cell
  3. Act as a template for protein synthesis
  4. Act as an energy currency
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Correct answer: (d) Act as an energy currency

ATP is the molecule in which energy is carried from where it is released to where it is spent.

23.The quantitative study of energy relationships in a biological system is called? (PMC MDCAT 2022)

  1. Bioenergetics
  2. Biochemistry
  3. Biotechnology
  4. Biophysics
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Correct answer: (a) Bioenergetics

The study of energy changes in living systems is bioenergetics.

24.Oxidative phosphorylation during the respiratory electron transport chain requires: (PMC MDCAT 2022)

  1. NAD+ as oxidising agent
  2. NADP+ as oxidising agent
  3. Molecular oxygen
  4. Light energy
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Correct answer: (c) Molecular oxygen

Oxygen is the last acceptor of the electrons, and without it the chain stops.

25.How many phosphate groups are present in nicotinamide adenine dinucleotide phosphate? (PMC MDCAT 2022)

  1. 1
  2. 2
  3. 3
  4. 4
Show answer

Correct answer: (c) 3

NADP carries the two phosphates of the dinucleotide and one more on the ribose, three in all.

26.In glycolysis, the conversion of Glucose-6-phosphate to fructose-6-phosphate involves: (PMC MDCAT 2022)

  1. Phosphorylation
  2. Oxidation
  3. Isomerization
  4. Reduction
Show answer

Correct answer: (c) Isomerization

An aldose is rearranged into a ketose with no atoms gained or lost, which is isomerization.

27.Which of the following chemical activity is involved in the conversion of pyruvate into acetaldehyde during anaerobic respiration? (PMC MDCAT 2022)

  1. Reduction
  2. Decarboxylation
  3. Oxidation
  4. Phosphorylation
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Correct answer: (b) Decarboxylation

Pyruvate loses a molecule of carbon dioxide to give acetaldehyde.

28.Which of the following releases 7.3 kCal energy when terminal phosphate is lost? (PMC MDCAT 2022)

  1. NADP
  2. ADP
  3. ATP
  4. FAD
Show answer

Correct answer: (c) ATP

Hydrolysing the terminal phosphate of ATP releases about $7.3\,\mathrm{kcal}$ a mole.

29.To reduce one molecule of O2, _ _ _ electron(s) must be passed through the electron transport chain and _ _ _ molecule(s) of NADH ls(are) oxidized (PMC MDCAT 2022)

  1. 1:1
  2. 4:4
  3. 1:2
  4. 4:2
Show answer

Correct answer: (d) 4:2

Oxygen takes four electrons and four protons to give two molecules of water, and each NADH gives two electrons.

30.Which of the following is the correct path of alcoholic fermentation? (PMC MDCAT 2022)

  1. Glycolysis –> Reduction
  2. Glycolysis –> Reduction –> Decarboxylation
  3. Glycolysis –> Decarboxylation –> Reduction
  4. Glycolysis –> Link reaction –> Kreb cycle –> ETC
Show answer

Correct answer: (c) Glycolysis –> Decarboxylation –> Reduction

Glucose is broken to pyruvate, the pyruvate loses carbon dioxide, and the acetaldehyde is reduced to ethanol.

31.The initial process of breaking down glucose is called (PMC MDCAT 2022)

  1. Reduction
  2. Glycolysis
  3. Chemiosmosis
  4. Oxidation
Show answer

Correct answer: (b) Glycolysis

Glycolysis is the first stage, in which glucose is split to pyruvate.

32.What is the net gain of ATP In glycolyslis, if it occurs during anaerobic respiration? (PMC MDCAT 2022)

  1. 2 ATP/glucose molecule
  2. 4 ATP/glucose molecule
  3. 6 ATP/glucose molecule
  4. 8 ATP/glucose molecule
Show answer

Correct answer: (a) 2 ATP/glucose molecule

Four ATP are made and two spent, so the net gain is two.

33.Which respiration is directly involved in the production of energy, necessary for all living activities? (PMC MDCAT 2022)

  1. Organismic
  2. Cellular
  3. Breathing
  4. External respiration
Show answer

Correct answer: (b) Cellular

Cellular respiration is where the energy of food is actually released into ATP.

34.One ATP molecule contains 1% of total energy of glucose. In anaerobic reactions how much energy of glucose is released as ATP: (PMC MDCAT 2022)

  1. 1%
  2. 2%
  3. 36%
  4. 38%
Show answer

Correct answer: (b) 2%

Anaerobic respiration nets two ATP from a glucose molecule, that is about two per cent of its energy.

35.In aerobic respiration, chemiosmosis occurs during : (PMC MDCAT 2022)

  1. Electron transport chain
  2. Photophosphorylation
  3. Glycolysis
  4. Kreb's cycle
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Correct answer: (a) Electron transport chain

Protons pumped by the electron transport chain return through ATP synthase, and that is chemiosmosis.

36.Which of the following is the final electron acceptor in the respiratory electron transport chain? (PMC MDCAT 2022)

  1. NADP+
  2. Molecular oxygen
  3. PS-I
  4. PS-II
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Correct answer: (b) Molecular oxygen

Oxygen takes the electrons at the end of the chain and is reduced to water.

37.oxygen is available, the complete breakdown of glucose produces ----- ATP molecules in prokaryotes: (NUMS MDCAT 2022)

  1. 20
  2. 36
  3. 38
  4. 40
Show answer

Correct answer: (c) 38

A prokaryote has no mitochondrial membrane to cross, so it nets the full thirty-eight.

38.It is the most energy rich compound. (PMC Practice 2021)

  1. FADH2
  2. ATP
  3. NADH
  4. GTP
Show answer

Correct answer: (c) NADH

Each NADH yields about three ATP, more than any of the others here.

39.Carbohydrate catabolism is concerned with the fate of: (PMC Practice 2021)

  1. ATP
  2. Glucose
  3. Aminoacid
  4. All of these
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Correct answer: (b) Glucose

Carbohydrate catabolism is the breaking down of glucose.

40.What is the final product of the Krebs cycle? (PMC Practice 2021)

  1. Malate
  2. Succinate
  3. Oxaloacetate
  4. Fumarate
Show answer

Correct answer: (c) Oxaloacetate

Oxaloacetate is regenerated at the end of each turn, ready to take the next acetyl group.

41.What are the end products of the electron transport chain in animals? (PMC Practice 2021)

  1. ATP
  2. Carbon dioxide
  3. Water
  4. Both Options A and C are correct
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Correct answer: (d) Both Options A and C are correct

The chain makes ATP and leaves water where the electrons and protons meet the oxygen.

42.The end product in anaerobic respiration is: (PMC MDCAT 2020)

  1. Ethanol and Carbon dioxide
  2. Lactate
  3. Pyruvate
  4. Both A and B
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Correct answer: (d) Both A and B

Yeast ferments to ethanol and carbon dioxide, muscle to lactate.

43.The end product of glycolysis in acrobic respiration is (PMC MDCAT 2020)

  1. Ethanol and carbon dioxide
  2. Lactate
  3. Pyruvate
  4. Acetyl CoA
Show answer

Correct answer: (c) Pyruvate

With oxygen present, glycolysis ends at pyruvate, which then enters the mitochondrion.

44.How many molecules of ATP would be utilized for phosphorylation of one glucose molecule during glycolysis? (UHS MDCAT 2019)

  1. Three
  2. Two
  3. Four
  4. One
Show answer

Correct answer: (b) Two

Two ATP are spent in phosphorylating the glucose before any is made.

45.Glycolysis takes place in the ______ of cells. (UHS MDCAT 2019)

  1. Nucleus
  2. Mitochondria
  3. Golgi complex
  4. Cytoplasm
Show answer

Correct answer: (d) Cytoplasm

Glycolysis needs no organelle and goes on in the cytoplasm.

46.The enzymes required for the Kreb cycle are found in ________. (UHS MDCAT 2018)

  1. F1 particles
  2. Lysosomes
  3. Cytoplasm
  4. Matrix
Show answer

Correct answer: (d) Matrix

The Krebs cycle enzymes are dissolved in the mitochondrial matrix.

47.In aerobic respiration (UHS MDCAT 2018)

  1. Pyruvate is completely oxidized to form carbon dioxide and water
  2. Pyruvate is completely oxidized to form oxygen and water
  3. Pyruvate carboxylated to produce citrate
  4. Pyruvate is converted to ethanol and carbon dioxide
Show answer

Correct answer: (a) Pyruvate is completely oxidized to form carbon dioxide and water

With oxygen present the pyruvate is oxidized right through to carbon dioxide and water.

48.At the last step of Glycolysis, which of the following compound is formed: (UHS MDCAT 2018)

  1. Pyruvic acid/ Pyruvate
  2. Lactic acid
  3. Ethyl Alcohol
  4. Fructose Phosphate
Show answer

Correct answer: (a) Pyruvic acid/ Pyruvate

Glycolysis ends at pyruvate.

49.The enzymes required in Glycolysis are present in: (UHS MDCAT 2018)

  1. Golgi Apparatus
  2. Cell cytoplasm
  3. Inner Mitochondrial Membrane
  4. Matrix of Mitochondria
Show answer

Correct answer: (b) Cell cytoplasm

Glycolysis needs no organelle and goes on in the cytoplasm.

50.In Citric Acid Cycle Acetyl CoA combines with: (UHS MDCAT 2017)

  1. Glucose
  2. CO2
  3. Rubisco
  4. Oxaloacetate
Show answer

Correct answer: (d) Oxaloacetate

Acetyl coenzyme A joins oxaloacetate to give citrate and start the cycle.

51.The term glycolysis refers to the conversion of: (UHS MDCAT 2017)

  1. Pyruvate to Glucose
  2. Glucose to Pyruvate
  3. Citric acid to CO2
  4. Both Pyruvate to Glucose and Glucose to Pyruvate
Show answer

Correct answer: (b) Glucose to Pyruvate

Glycolysis is the splitting of glucose to two molecules of pyruvate.

52.Malate is oxidized by (UHS MDCAT 2015)

  1. ATP
  2. NADP to oxaloacetate in Krebs’s Cycle.
  3. NAD
  4. FAD
Show answer

Correct answer: (c) NAD

Malate dehydrogenase passes the hydrogen to NAD.

53.In electron transport chain, the electrons from NADH and FADH2 are passed to; (UHS MDCAT 2015)

  1. Cytochrome a
  2. Cytochrome a3
  3. Co-enzyme c
  4. Co-enzyme Q
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Correct answer: (d) Co-enzyme Q

Both feed their electrons into coenzyme Q, which passes them along the chain.

54.Carriers of the respiratory chain are located on: (UHS MDCAT 2015)

  1. Matrix of mitochondria
  2. Outer membrane of mitochondria
  3. Inner membrane of mitochondria
  4. Cytoplasmic matrix
Show answer

Correct answer: (c) Inner membrane of mitochondria

The carriers sit in the inner mitochondrial membrane.

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