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

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

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'

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

Respiratory substrate yielding maximum number of ATP molecules is

  1. Ketogenic amino acids

  2. Glucose

  3. Amylose

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

The process of glycolysis in respiration requires glucose as the primary substrate to be oxidised. Any other substrate is first converted to glucose before it can enter glycolysis. Certain substrates like ketogenic amino acids, amylose, glycogen need to be converted to glucose first at a cost of some energy in the form of ATP. Hence their net yield of ATP is less than that of glucose as a substrate.

So the answer is 'Glucose'.

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

Metabolism of one palmitic acid yields 

  1. 36 ATP

  2. 56 ATP

  3. 129 ATP

  4. 48 ATP
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Oxidation of palmitic acid yields 7 NADH + 7 FADH2 + 8 acetyl-CoA in 7 cycles of mitochondrial beta-oxidation. Every acetyl-CoA yields 3 NADH + 1 FADH2 + 1 GTP (=ATP) during Krebs cycle. An average production of 3 ATP/NADH and 2 ATP/FADH2 using the respiratory chain, We get  131 ATP molecules. However, you have to use 2 ATP molecules for the initial activation of every fatty acid that is going to be oxidized in the mitochondria.

So the correct option is '129 ATP'.

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

How many ATP molecules are released when one molecule of glucose is oxidised in our liver cells?

  1. 36

  2. 38

  3. 2

  4. 8
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

38 ATP molecules are produced for the oxidation of one molecule of glucose. 2 from glycolysis, 2 from the Citric acid cycle, and about 34 from the electron transport system.

So the correct option is '38.'

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

How many ATPs are formed per glucose molecule in Krebs cycle?

  1. 2

  2. 24

  3. 6

  4. 28
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

During the process of Krebs cycle 2 molecules of ATP, 8 molecules of NADH and 2 molecules of FADH2 were produced per molecule of glucose. A total of 28 ATPs are produced during Krebs cycle per a glucose molecule.

So the correct option is '28.'

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

From the oxidation of one molecule of palmitic acid (fatty acid), the number of ATP molecules gained as net are

  1. $131$
  2. $129$
  3. $38$
  4. $142$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The oxidation of fatty acid occurs in the following step in mitochondria:

1. activation of fatty acid
2. beta-oxidation
3. Kreb's cycle
Palmitic acid is made up of 16 carbons, so going by the formula C$ _{2n}$, then 2n=16 for palmitic acid, hence, n=8. So, 8 acetyl Co-A are produced. Now, n-1 will be the number of NADH and FADH$ _{2}$ produced, so, n-1=7 for palmitic acid. Hence, there will be 7 FADH$ _{2}$ and 7 NADH.
Now, 1 NADH gives 3 ATP, so 7 NADH will give 21 ATP
          1 FADH$ _{2}$ gives 2 ATP, so 7  FADH$ _{2}$ will give 14 ATP
          1 Acetyl Co-A through Kreb's cycle gives 12 ATP, so 8 Acetyl Co-A will give 96 ATP.
Hence, a total of 131 ATP will be formed. But 2 ATPs have been used in the activation of the fatty acid in the first step so, 131-2=129 ATPs as net will be formed. 
Hence, the correct answer is '129'

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

In aerobic respiration,if 38 molecules of ATP are produced,then the number of ATP produced in glycolysis (X), pyruvate to acetyl- CoA (Y) and Krebs cycle (Z) will be

  1. X- 2,Y-6,Z-30

  2. X-8,Y-6,Z-24

  3. X-8,Y-10,Z-24

  4. X-2,Y-12,Z-24
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  •  Glycolysis: (2 ATP)
ATP formation by substrate phosphorylation = 4 ATP
ATP consumed in Glycolysis = 2 ATP 
  •  Pyruvate to Acetyl CoA: (2 NADH$ _{2}$ = 6 ATP) 
  • Kreb's Cycle: (30 ATP)
ATP formation by substrate phosphorylation = 2 ATP
ATP formation by oxidative phosphorylation = 28 ATP
So, the correct option is 'A) X- 2, Y - 6 ,Z-30'.