Biology

Cellular Respiration and Enzymes

1,551 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

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 '

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

Mark the incorrect statement

  1. The breaking of c-c bonds of complex organic molecules by oxidation cells leading to the release of a lot of energy is called cellular respiration

  2. Initial stage of cellular respiration takes place in cytoplasm

  3. Incomplete oxidation of pyruvate by stepwise removal of all the hydrogen atoms leaving 3 molecules of CO2

  4. TCA cycle starts with condensation of acetyl group with OAA and water to yield citric acid
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Aerobic respiration is comprised by

1) The complete oxidation of pyruvate by stepwise removal of all hydrogen atoms leaving 3 molecules of CO$ _2$. 
2) The passing of the electrons removed as apart of the hydrogen atoms to molecular O$ _2$with the simultaneous synthesis of ATP.
So, the incorrect statement is ' Incomplete oxidation of pyruvate by stepwise removal of all hydrogen atoms leaving 3 molecules of CO$ _2$'.
rest all are correct statements w.r.t. Respiration. 

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

Out of $36$ ATP molecules produced per glucose molecule during respiration.

  1. $2$ are produced outside glycolysis and $34$ during respiratory chain
  2. $2$ are produced outside mitochondria and $34$ inside mitochondria
  3. $2$ during glycolysis and $34$ during Krebs cycle

  4. All are formed inside mitochondria
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process, as weak so-called "high-energy" bonds are replaced by stronger bonds in the products. Respiration is one of the key ways a cell releases chemical energy to fuel cellular activity.  The chemical energy stored in ATP (its third phosphate group is weakly bonded to the rest of the molecule and is cheaply broken allowing stronger bonds to form, thereby transferring energy for use by the cell) can then be used to drive processes requiring energy. Since the cellular respiration happens inside mitochondria, and glucose being given out as a by-product, glucose is produced inside and outside mitochondria.

So the correct option is '2 are produced outside mitochondria and 34 inside mitochondria'.

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

Complete oxidation of a molecule of glucose yields?

  1. $15$ ATP molecules
  2. $2$ ATP molecules
  3. $36$ ATP molecules
  4. $8$ ATP molecules
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Oxidation is a chemical process that, loosely defined, involves removing electrons from particular areas of a molecule. In biochemical processes, oxidation generally results in the release of energy. The glucose molecule contains stored energy in its bonds, just as other nutrient molecules do, including starch, proteins and fats. When you consume food that contains glucose, you digest the food and absorb the glucose into your bloodstream. From there, cells take up the glucose and either store it for later use or chemically burn it to provide energy. Oxidation of glucose is analogous to burning wood in many ways: It releases chemical energy. The complete aerobic oxidation of glucose is coupled to the synthesis of as many as 36 molecules of ATP.

So the correct option is '36 ATP molecules'.

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

Number of ATP obtained at the end of Kreb's cycle?

  1. $2$ ATP
  2. $4$ ATP
  3. $36$ ATP
  4. $38$ ATP
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For every molecule of glucose, two molecules of acetyl-CoA enter the Krebs cycle, each producing one GTP (which is readily converted to ATP) through substrate-level phosphorylation. Thus, a total of 2 ATP molecules are obtained directly per glucose molecule from the Krebs cycle.

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

How many ATP molecules will be produced when one molecule of $3$-phosphophoglyceric acid is completely oxidised?

  1. $16$
  2. $17$
  3. $32$
  4. $20$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

3-phosphoglyceric acid is an intermediate in glycolysis. Its oxidation involves conversion to pyruvate and subsequent entry into the Krebs cycle and ETC, yielding approximately 16 ATP.

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

The incremental oxidation of 1 molecule of glucose during cellular respiration produces 30 molecules of ATP according to the balanced equation:
$C _6H _{12}O _6+6O _2+30ADP+30P _i\rightarrow 6H _2O+6CO _2+30ATP$
ATP is then hydrolyzed by cells for a variety of biochemical processes.
Changes in free energy between glucose oxidation and ATP hydrolysis were compared. The table below illustrates the data collected:

Reaction Change in Free Energy ($\triangle G$)
Glucose Oxidation -686 kcal/mol
ATP Hydrolysis -13 kcal/mol

Which statement best explains the data?

  1. Both glucose oxidation and ATP hydrolysis, are exergonic because they have negative $\triangle G$ values.

  2. Both glucose oxidation and ATP hydrolysis, are exergonic because their products have more free energy than their reactants.
  3. Both glucose oxidation and ATP hydrolysis, are endergonic because they have negative $\triangle G$ values.

  4. Both glucose oxidation and ATP hydrolysis, are endergonic because their products have less free energy than their reactants.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Both ATP and Glucose oxidation are energy releasing or exergonic processes as the value of $\delta$G is negative

So, the correct answer is 'Both glucose oxidation and ATP hydrolysis, are exergonic because they have negative △G△G values'