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 biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

ATP is produced by oxidative phosphorylation in

  1. Glycolysis.

  2. Krebs cycle.

  3. Chemiosmosis.

  4. B and C only.

  5. A, B and C.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Glycolysis and Kreb's cycle form total 4 ATPs by substrate level phosphorylation wherein the direct transfer of phosphate group to ADP or GDP during chemical reactions leads to the synthesis of ATP/GTP. Oxidative phosphorylation is the process wherein oxidation of reducing equivalent generate energy to drive ATP synthesis. Chemiosmosis includes the use of proton gradient generated across the inner mitochondrial membrane, during transfer of electrons from NADH and FADH$ _2$ to O$ _2$, to drive ATP synthesis. During chemiosmosis, 10 molecules of NADH power synthesis of 10*3 = 30 ATP while 2 molecules of FADH$ _2$ power synthesis of 2*2 = 4 ATP.
Thus, the correct answer is option C.
Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Electron carriers such as nicotinamide adenine dinucleotide (NAD) are used in energy capturing processes such as photosynthesis and respiration. They play a central role in the redox reactions that occur at the time of energy harvest from the carbon source.
What is the function of an oxidizing agent?

  1. Molecules that donate electrons.

  2. A molecule that becomes oxidized.

  3. A molecule that gains electrons.

  4. Molecules that combines with oxygen.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

NAD$^+$ accepts electrons/H$^+$ released by water.

So, the correct answer is 'A molecule that gains electrons'

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Terminal oxidation comprises

  1. Synthesis of metabolic water

  2. Electron transport

  3. Oxidative phosphorylation

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

The respiratory breakdown of glucose in the presence of oxygen is an oxidative process. During this process, several intermediates such as pyruvic acid, isocitric acid, succinic acid and oxalic acid are oxidized. Each oxidation step involves the release of 2 H which goes to reduce various coenzymes i.e. NAD+ and FAD. Reduced NAD+ and FAD released in the glycolysis and Krebs cycle finally reduce oxygen to water. This transfer of H+ and e- from NADH + H+ or FADH2 to oxygen is not a simple process and the direct transfer of electrons from coenzymes to oxygen is thermodynamically not possible. To facilitate this transfer, many intermediate cytochromes and other carriers are arranged in a series which transport electrons from NADH or FADH2 to oxygen. This sequence of electron carriers constitutes electron transport system. The electron transport proceeds from carriers that have low redox potential to those having high redox potential. The electron transport down to the energy gradient through electron transport system leads to the formation of ATP from ADP and inorganic phosphate. This generation of ATP is called oxidative phosphorylation. 

Thus, the correct answer is option D. 

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

When a pair of electrons from NADH+$H^+$ transported through respiratory ETS, results in the formation of 

  1. 2 ATPs

  2. 4 ATPs

  3. 3 ATPs

  4. 5 ATPs
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  • Glycolysis and Krebs cycle yield certain reduced coenzymes like NADH+H+ and FADH2.
  • ETS is metabolic pathway of electron transport that oxidizes these coenzymes to release energy from them.
  • NADH+H+ gets oxidized at Complex I of ETS and as the electrons are transferred to other Complexes, it creates a proton gradient for ATP production. One NADH+H+ yields 3 ATPs and one FADH2 yields 2 ATPs.
  • So the correct answer is '3 ATPs'.
Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Oxidative phosphorylation is production of

  1. ATP in photosynthesis

  2. NADH in photosynthesis

  3. ATP in respiration

  4. NADH in respiration
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Formation of ATP from ADP in the presence of oxygen during the Krebs cycle is known as oxidative phosphorylation.

This takes place in mitochondria of the cell during oxidative phosphorylation a total of 28 ATP are formed.
So the correct option is 'ATP in respiration'

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

ATP is produced during

  1. Cyclic photophosphorylation

  2. Non cyclic photophosphorylation

  3. Both (A) and (B)

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

ATP is produced during both cyclic and non-cyclic photophosphorylation. During non-cyclic photophosphorylation when electrons move from PS II to PS I, then ATP and $NADPH _2$ is generated and during cyclic photophosphorylation only ATP is generated.

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Which is product of oxidative pentose phosphate pathway?

  1. Pyruvic acid

  2. Acetyl CoA
  3. NADH$ _2$

  4. NAD(P)H

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

Pentose phosphate pathway or HMP is an oxidative phosphate pathway of cellular respiration in which glucose 6-phosphate acts as the substrate. After its complete oxidation through HMP, 12 NADPH + H+ and 6 CO2 are formed. This pathway is an alternate pathway to glycolysis and is seen in RBC, adrenal cortex, liver, etc. A net gain of 35 ATP is achieved through this pathway.

So the answer is 'NAD(P)H'.

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

One molecule of NADH and one molecule of $FADH _2$ yield

  1. 2 and 3 ATP

  2. 18 and 36 ATP

  3. 36 and 18 ATP

  4. 3 and 2 ATP

  5. 2 and 36 ATP
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Reduced molecules like NADH+H+ and FADH2 yield energy in the form of ATP when they undergo ETC in mitochondria. NADH+H+ enter ETC at higher complex than FADH2 so they release energy as 3 ATP and 2 ATP respectively.

So the answer is '3 and 2 ATP'.

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

FAD is electron acceptor in citric acid cycle during the oxidation of

  1. Malic acid to oxaloacetatic acid.

  2. Succinic acid to malic acid.

  3. Citric acid to -ketoglutaric acid.
  4. $\alpha$-ketoglutaric acid to succinic acid.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The Krebs cycle is the condensation of acetyl group with oxaloacetic acid and water to yield citric acid and leads to the formation of Oxalo acetic acid.

Eighth step in which Succinic acid converts into Fumaric acid in the presence of enzyme succinic dehydrogenase release energy and form FADH which yields 2ATP.
So the correct option is 'Succinic acid to Fumaric acid.'

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

The process of phosphorylation takes place in

  1. Glycolysis

  2. Kreb's cycle

  3. HMP pathway

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

Phosphorylation is the addition of a phosphate (PO$ _{4}^{3-}$) group to a protein or other organic molecule. Phosphorylation results in the formation of ATP, which is the energy currency of cell. Phosphorylation occurs as a part of glycolysis, Kreb's cycle and HMP pathway.

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

In oxidative phosphorylation, oxidation and phosphorylation take place simultaneously and forms:

  1. NADP

  2. DPN

  3. Pyruvic acid

  4. ATP

  5. Both B and D
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Oxidative phosphorylation refers to synthesis of ATP by ADP and Pi driven by energy released from oxidation of reducing powers NADH and FADH2 by transfer of their electrons through electron trasnport chain to oxygen. Electron trasnport chain is present in inner mitochondrial membrane and passes the electrons down a series of carriers and pump protons into the intermembrane space. Oxygen serves as final electron acceptor in oxidation of NADH and FADH2 and the resulting proton gradient serves as energy source for the enzyme ATP synthase to synthesize ATP. So final products of oxidative phosphorylation are ATP, NAD and FAD. DPN (diphosphopyridine nucleotide), also called as NAD. Correct answers are D and B. NADP is coenzyme of photosynthetic light reactions. Puruvic acid is product of glycolysis. 

Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Oxidative phosphorylation is the formation of 

  1. NADPH$ _{2}$ in respiration

  2. ATP in respiration
  3. NADPH$ _{2}$ in photosynthesis

  4. ATP in photosynthesis
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Oxidative phosphorylation is the metabolic pathway in which the mitochondria in cells use their structure, enzymes and energy released by the oxidation of nutrients to reform ATP in respiration.