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 bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

During which stage in the complete oxidation of glucose are the greatest number of ATP molecules formed from ADP -

  1. Glycolysis

  2. Krebs cycle

  3. Electron transport chain

  4. Conversion of pyruvic acid to acetyl CoA
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In glycolysis 4 ATP and 2NADH2 molecules are formed. These 2NADH2  molecules go to electron transport chain. In oxidative decarboxylation no ATP molecule is formed but two molecules of 2NADH2  are formed from two molecules of pyruvate. These two NADH2 go to electron transport chain. In Kreb's cycle 2 ATP, 6NADH2 and 2FADH2 molecules are formed from two molecule of acetyl Co-A. These NADH2 and 2FADH2  go to electron transport chain. In electron transport chain all 2NADH2   and 2FADH2  pass to electron carriers and yield 3 ATP and 2 ATP molecules per 2NADH2   and 2FADH2  respectively. Thus,  4 ATP are formed in glycolysis, 2 ATP in Krebs cycle and 34 ATP from electron transport chain. 40 ATP and 2 ATP molecules are used during glycolysis. So, net gain of ATP molecules during one complete oxidation of a glucose molecule is 38 ATP.


So, the correct answer is 'Electron transport chain'.

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Out of $38$ ATP molecule how many ATP are formed by substrate level phosphorylation by aerobic respiration of $1$ glucose?

  1. $2$
  2. $3$
  3. $4$

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

Substrate level phosphorylation involves the conversion of 1,3 bisphosphoglycerate to 3 phosphoglycerate producing ATP.

For 1 molecule of glucose, 2 (1,3 bisphosphoglycerate) are formed, hence 2 ATP are formed.  

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Number of ATP molecules formed during aerobic respiration in break down of one glucose molecule via malate aspartate shuttle is 

  1. 38

  2. 18

  3. 28

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

In aerobic respiration, the malate-aspartate shuttle is more efficient than the glycerol-3-phosphate shuttle. It results in the production of 38 ATP molecules per glucose molecule in prokaryotes or specific eukaryotic tissues.

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

If $4$ molecules of glucose are synthesized during photosynthesis, how many ATP molecules are released and how many molecules of ATP are utilized respectively?

  1. $8 ATP, 72 ATP$
  2. $2 ATP, 18 ATP$
  3. $8 ATP, 36 ATP$
  4. $4 ATP, 36 ATP$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
For the synthesis of one molecule of glucose by photosynthesis, 2 ATP molecules are released and 18 ATP molecules are utilized. 18 ATP molecules are utilized in the sense that in most of the plants the mode of CO$ _2$ fixation is C$ _3$ cycle or Calvin cycle. In C$ _3$ cycle for each molecule of CO$ _2$ to be fixed, 3 ATP are required. Thus, for the synthesis of one Glucose molecule, 6 CO$ _2$ molecules are fixed. Thus, 18 ATP molecules in total are utilized for the formation of one Glucose molecule.
Hence, for the synthesis of 4 glucose molecules in photosynthesis,
ATP molecules released = 4 × 2 = 8
ATP molecules utilized = 4 × 18 = 72.
So, the correct answer is A.
Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Choose the correct answers from the alternatives given :
In eukaryotes complete oxidation of a glucose molecule results in the net gain of how many ATP molecules?

  1. 2

  2. 4

  3. 36

  4. 38
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Complete oxidation of glucose occurs through three steps : 

  1. Glycolysis
  2. Krebs cycle
  3. Terminal oxidation
During glycolysis glucose changes to pyruvic acid gaining total energy as 2 ATP molecules and 2 molecules of NADH$ _2$ then later on in Krebs cycle 30 ATP molecules and 2 FADH$ _2$ are produced. One NADH$ _2$ produces 3 ATP molecules while one FADH$ _2$ produces two ATP molecules. Therefore in complete oxidation of one molecule of glucose, a total of 38 ATP's are gained.
So, the correct option is ' 38'. 

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell


In aerobic cellular respiration, most of the ATP is synthesized during:

  1. Electron transport

  2. Glycolysis

  3. Krebs cycle

  4. Oxidation of pyruvic acid
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cellular respiration occurs in three steps :

  1. Glycolysis 
  2. Krebs cycle 
  3. Terminal oxidation 
Glycolysis is the breakdown of glucose into two molecules of pyruvate where 2 NADH and 2 ATP molecules are formed which in total is 8 ATP molecules as 1 NADH = 3 ATP, While in Krebs cycle reaction occurs in mitochondria where 10 NADH molecules, 2 FADH, and 4 ATP molecules are formed, in total 38 ATP molecules are formed .
So, the correct option is ' Krebs cycle'.

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Choose the correct answers from the alternatives given :
Which one of the following is the energy currency of the cell?

  1. AMP

  2. ADP

  3. ATP

  4. NADP
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

ATP ( Adenosine triphosphate ) is the energy currency of the cell, it helps in the completion of all the metabolic processes by utilization of its phosphorus molecule. It is generated by mitochondria. One molecule of ATP releases around 30.5 kJ /mol of energy.

So, the correct option is ' ATP'.

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Choose the correct answers from the alternatives given :
Of the 36 ATP molecules that are produced during the complete breakdown of glucose, most are due to the action of 

  1. substrate-level phosphorylation

  2. electron transport system

  3. chemiosmotic phosphorylation

  4. both (b) and (c)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Substrate level phosphorylation is the part of glycolysis reaction whihc will give the cell 2 molecules of ATP at the end of the reaction.
  • Electron transport system is the transport system that is present in the mitochondrial membrane where it transports the electrons and hydronium ions from NADH and FAD through various complex of the chain.
  • In chemiosmotic phosphorylation the $F _1$-$F _0$ complex is used for the synthesis of one molecule of ATP for every 2 hydronium ion that is transported through the complex from the intermembrane matrix.
  • For each NADH transported through the chain 3 times 2 hydronium ions are released which means every molecule of NADH produces 3 molecules of ATP. For every FADH molecules passed 2 times 2 hydronium are released which means that every molecule of FADH gives 2 ATP molecules.
  • Therefore when per pyruvic acid after going under kerb cycle gives 4 NADH and 1 FADH molecule that gives the cell with  12 ATP and 2 ATP molecules respectively per cycle.
  • Therefore ETS and the chemisomotic phosphorylation give the major contribution in the formation of ATP i.e. 15 ATP per cycle.
  • Therefore the answer option 'both (b) and (c)' is correct.
Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Choose the correct answers from the alternatives given :
The greatest contributor of electrons to the electron transport system is

  1. oxygen

  2. transition reaction

  3. glycolysis

  4. Krebs cycle
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Electron transport system is the transport system that is present in the mitochondrial membrane where it transports the electrons and hydronium ions from NADH and FAD through various complex of the chain.
  • In chemiosmotic phosphorylation the $F _1$-$F _0$ complex is used for the synthesis of one molecule of ATP for every 2 hydronium ion that is transported through the complex from the intermembrane matrix.
  • For each NADH transported through the chain 3 times 2 hydronium ions are released which means every molecule of NADH produces 3 molecules of ATP. For every FADH molecules passed 2 times 2 hydronium are released which means that every molecule of FADH gives 2 ATP molecules.
  • Therefore when per pyruvic acid after going under kerb cycle gives 4 NADH and 1 FADH molecule that gives the cell with  12 ATP and 2 ATP molecules respectively per cycle.
  • Therefore it can be said that kerb cycle is the major contributor to the electron that are provides to the ETS for the production of ATP.
  • Therefore option 'Krebs cycle' is the correct answer.
Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

How many ATP molecules will be generated in a plant system during complete oxidation of $40$ molecules of glucose?

  1. $180$
  2. $360$
  3. $1440$
  4. $3040$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$36 $ ATP molecules are produced during complete oxidation of one molecule of glucose.
So, $40$ molecules of glucose will produce $(36 \times 40) ATP= 1440$ ATP.

So the correct option is C.

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

The net yield of ATP, except substrate-level phosphorylation, from Krebs cycle per glucose molecule is

  1. $12$
  2. $24$
  3. $22$
  4. $36$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

From one molecule of glucose, 38 ATP molecules can be produced during cellular respiration. Glycolysis produces net 2 ATP molecules by substrate level phosphorylation. Kreb cycle produces 2 ATP molecules by substrate level phosphorylation. About 34 ATP are produced from oxidative Phosphorylation. During Kreb cycle, 6 molecules of NAD$^+$ are reduced to NADH and 2 molecules of FAD are reduced to FADH$ _2$. Now 6 NADH produce 6 x 3 = 18 ATP molecules. Similarly, 2 FADH$ _2$ produce 2 x 2 = 4 ATP molecules. Hence, total 18 + 4 = 22 molecules of ATP are produced per glucose molecule from Kreb cycle except substrate level phosphorylation.

Thus, the correct answer is '22.'

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

If one triose phosphate completely oxidized inside prokaryotic cell than gain of ATP of energy equal to?

  1. $5$ ATP
  2. $4$ ATP
  3. $20$ ATP
  4. $19$ ATP
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Triose phosphate is another name of glyceraldehyde 3- phosphate

Total NADH and ATP are produced in the cycle are as follows as -

 Name of process  Gain of ATP
 Glycolysis: glyceraldehyde 3- phosphate $\rightarrow$pyruvate  1 NADH ( each NADH is equal to 3 ATP) + 1 ATP3ATP+ 1ATP = 4ATP
 Oxidative decarboxylation pyruvate $\rightarrow$acetyl CoA  1 NADH = 3 ATP
 Tricarboxylic acid cycle  3NADH +1 FADH (each FADH is equal to 2ATP) + 1 GTP(equivalent to ATP) =  12 ATP

Total gain of ATP, when one triose phosphate is completely oxidised =  4 ATP =3 ATP =12 ATP $\rightarrow$  19 ATP

So, the correct answer is ' 19 ATP '