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 is the first step of glycolysis?

  1. Cleavage of Fructose-1,6-diphosphate

  2. Phosphorylation of glucose

  3. Oxidative dehydrogenation

  4. Isomerisation

  5. Dehydration
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Glycolysis starts with the phosphorylation of glucose in G-6-P by using two ATP molecules in the presence of hexokinase enzyme.

Multiple choice

The set of enzymes important for the regeneration of RUBP are

  1. aldolase and fumerase

  2. phosphatase and transketolase

  3. aldolase and transketolase

  4. isomerase and sucrase

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Aldolase and transketolase are key enzymes regenerating RuBP. Aldolase forms carbon-carbon bonds; transketolase rearranges sugar phosphates to restore RuBP for continued CO2 fixation.

Multiple choice

The conditions under which RUBP carboxylase starts behaving as RUBP oxygenase are

  1. high temperature and high oxygen concentration

  2. low temperature and high oxygen concentration

  3. high temperature and low oxygen concentration

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

RuBisCO functions as an oxygenase under high temperature and high oxygen concentration conditions, leading to photorespiration. Under normal conditions, it acts primarily as a carboxylase fixing CO2. Low temperature or low oxygen favor carboxylation, while the combination of high temperature and high O2 shifts its activity toward oxygenation.

Multiple choice

The first stable product of Crassulacean acid metabolism is

  1. PGA

  2. Malic acid

  3. Citric acid

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

In Crassulacean Acid Metabolism (CAM) plants, CO2 is fixed at night into oxaloacetate, which is then converted to malic acid and stored in vacuoles. Malic acid is the first stable product of this carbon fixation pathway. PGA is the first stable product in C3 plants, while citric and succinic acids are involved in the Krebs cycle, not CAM photosynthesis.

Multiple choice

Assertion (A): The inhibition of glycolysis by oxygen is referred to as Pasteur effect. Reason (R): This is due to inhibition of the enzyme phosphofructokinase by ATP and citrate (formed in the presence of O2).

Directions: In the following question, there are two statements, Assertion (A) and Reason (R), consider both the statements independently and mark your answer as:

1. if A and R both are correct and R is the correct explanation of A 
2. if A and R both are correct and R is not the correct explanation of A 
3. if A is correct and R is incorrect 
4. if A is incorrect and R is correct 
5. if A and R both are incorrect

  1. 1

  2. 2

  3. 3

  4. 4

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

Both Assertion (A) and Reason (R) are correct and R is the correct explanation of A. The inhibition of glycolysis by oxygen is referred to as Pasteur effect.  This is due to inhibition of the enzyme phosphofructokinase by ATP and citrate (formed in the presence of O2).