Biology

Cellular Respiration and Enzymes

1,721 Questions

Explore key concepts of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. These questions also cover ATP production, anaerobic respiration, and essential metabolic pathways. This topic forms a core part of the biology syllabus for many competitive examinations.

Glycolysis and metabolic pathwaysKrebs cycle processesElectron transport chainATP production countAnaerobic respiration products

Cellular Respiration and Enzymes Questions

Multiple choice

Which of the following enzymes belongs to the category of enzymes that act on the aldehyde or oxo group of donors?

  1. Pyruvate dehydrogenase

  2. Alcohol dehydrogenase

  3. NADH dehydrogenase

  4. Malate dehydrogenase

  5. Glycerol dehydrogenase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pyruvate dehydrogenase belongs to Category EC 1.2 of oxidoreductases (EC 1), act on the aldehyde or oxo group of donors. Pyruvate dehydrogenase performs the first two reactions within the pyruvate dehydrogenase complex: decarboxylation of pyruvate and reductive acetylation of lipoic acid.

Multiple choice

In which of the following steps of glycolysis, there is neither expenditure of energy nor formation of ATP?

  1. Phosphorylation of glucose to form glucose 6-phosphate.

  2. Conversion of fructose 6-phosphate to fructose 1,6 diphosphate.

  3. Splitting of fructose 1,6 diphosphate into two molecules of triose phosphates.

  4. Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate.

  5. Conversion of phosphoenol pyruvate to pyruvate.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Splitting of fructose 1,6 diphosphate into two molecules of triose phosphates, an aldotriose-glyceraldehyde 3-phosphate and one ketotriose - dihydroxy acetone phosphate is catalysed by the enzyme aldolase. There is neither expenditure of energy nor formation of ATP.

Multiple choice

The number of carbon dioxide molecules produced by the oxidation of one molecule of glucose during aerobic respiration is

  1. 2

  2. 4

  3. 6

  4. 8

  5. 10
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

During aerobic respiration, each carbon atoms in a glucose molecule is completely oxidized. Each oxidized carbon is released, along with two oxygen atoms, forming a molecule of carbon dioxide. Glucose contains 6 carbon atoms, thus the number of carbon dioxide molecules produced by the oxidation of one molecule of glucose during aerobic respiration is 6.

Multiple choice

Which of the following statements is/are false regarding glycolysis?

  1. Glycolysis occurs in the cytoplasm of the cell.
  2. All the steps in glycolysis are reversible.
  3. Pyruvate is the end product of glycolysis.

Select the correct answer using codes given below

  1. 1 only

  2. 2 only

  3. 3 only

  4. 1 and 2

  5. 1, 2 and 3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Three reactions of glycolysis have such a large negative ∆G in the forward direction that they are essentially irreversible.

Multiple choice

Match the entries in column I (enzymes) with that in column II (reactions catalysed by them during glycolysis) and select the correct answer.

 
Column - I
Column - II
P. Glucokinase 1. Conversion of glucose 6-phosphate to fructose 6-phosphate
Q. Phosphogluco isomerase 2. Phosphorylation of fructose 6-phosphate to produce fructose-1,6-diphosphate
R. Phosphofructokinase 3. Phosphorylation of glucose is to form glucose 6-phosphate

  1. P - 1, Q - 2, R - 3

  2. P - 3, Q -1, R - 2

  3. P - 2, Q -1, R - 3

  4. P - 2, Q - 3, R - 1

  5. P - 1, Q - 3, R - 2
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Glucose is phosphorylated to form glucose 6-phosphate by the enzyme glucokinase. Glucose 6-phosphate is converted to fructose 6-phosphate by the enzyme phosphogluco isomerise. Fructose 6-phosphate is phosphorylated irreversibly at 1 position catalyzed by the enzyme phosphofructokinase to produce fructose-1,6-diphosphate.

Multiple choice

Which of the following is not true about the chemisosmotic model?

  1. It was given by Peter Mitchell.

  2. The link between proton and ATP formation is an electrochemical potential across the membrane.

  3. It provides a very plausible explanation for the coupled ATP generation.

  4. The unidirectional pumping of protons accounts for the gradient and the capability of the gradient to drive ATP synthesis.

  5. F0F1 forms the ATP synthase complex.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The link between electron and ATP formation is an electrochemical potential across the membrane.

Multiple choice

The first event in the Calvin cycle is the attachment of carbon dioxide to the five carbon RuBP molecule, which ____________.

  1. forms a six carbon molecule that immediately breaks down into two three carbon PGA molecules

  2. is a reaction assisted by large quantities of RuBP carboxylase enzyme

  3. decreases cell carbon dioxide levels that increases the diffusion gradient

  4. 1, 2 and 3 are correct

  5. immediately becomes a six carbon sugar that is the base for starch, sucrose, cellulose, etc.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The Calvin cycle begins with CO2 fixation by RuBP carboxylase (Rubisco), forming an unstable 6-carbon intermediate that splits into two 3-carbon PGA molecules. This reaction is enzyme-assisted and helps maintain the diffusion gradient for CO2 uptake.

Multiple choice

The end product of the Calvin cycle is ________.

  1. ATP

  2. ribulose bisphosphate (RuBP)

  3. phosphoglyceraldehyde (PGAL)

  4. PEP carboxylase (PEPcase)

  5. Carbon dioxide
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Calvin cycle uses ATP and NADPH to fix carbon dioxide into G3P (phosphoglyceraldehyde), which is often referred to as PGAL.

Multiple choice

Identify the incorrectly matched pair.

  1. J. Sumner - Crystallisation of first enzyme

  2. F. A. Lipmang - Discovery of coenzyme-A and its role in metabolism

  3. E. Fischer and Krebs - Alteration of enzyme activity by phosphorylation/ dephosphorylation

  4. F. Sanger - Action of enzymes

  5. W. Arber, D. Nathans and Hamilton O. Smith - Discovery of restriction enzymes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

 Otto H. Warnburg gave action of enzymes. The Nobel Prize in Physiology or Medicine 1931 was awarded to Otto Warburg for his discovery of the nature and mode of action of the respiratory enzyme. The Nobel Prize in Chemistry 1958 was awarded to Frederick Sanger for his work on the structure of proteins, especially that of insulin.

Multiple choice

Directions: Read the following information and answer the given question.

Raman had his first day at gym today. He had exercised hard over there for the first time. After reaching home he realised his calves are paining. His mother advised him to take rest and not to get worried as he had got cramps. Raman followed his mother's advice.

Which pathway of respiration is used for breakdown of glucose during strenuous exercise?

  1. Aerobic respiration in mitochondria

  2. Anaerobic respiration

  3. Aerobic respiration in cytoplasm

  4. Fermentation
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When muscles work hard and oxygen is depleted, the body switches to anaerobic respiration to continue producing energy, resulting in lactic acid buildup.