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 biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Chemiosmosis hypothesis given by Peter Mitchell proposes the mechanism of

  1. Synthesis of NADH.

  2. Synthesis of ATP.
  3. Synthesis of FADH$ _2$.

  4. Synthesis of NADPH.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Chemiosmosis or chemiosmotic theory is given by Peter Mitchell explains the synthesis of ATP in the chloroplast. During the process of photosynthesis, the synthesis of ATP causes proton gradient to develop due to the accumulation of protons in thylakoid lumen that are formed by splitting of water. As the electron moves through the photosystem, protons are transported across the membrane. Now NADP reductase (enzyme) in stroma along with the electron acceptor removes protons along with the reduction of NADPH + H+. This causes proton gradient across the thylakoid membrane. The ATPase enzyme has a channel which allows the flow of proton through it and during this process the ATP is synthesised. Thus the correct answer is option B.
Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Major function of respiration is to produce

  1. NADH $(H^+)$

  2. ATP

  3. Pyruvate
  4. $C _2H _5OH$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Respiration is a process in which respiratory substrates are broken down through oxidation accompanying with the release of energy and its storage or conservation in the form of ATP with the release of carbon dioxide as a consequence. The actual mechanism of respiration is a stepwise process in which each step is catalyzed by a specific enzyme and the energy stored in the substrate is released in a stepwise series of reactions. The energy released in the process is used up in various energy-requiring processes of organisms. 

Thus, the correct answer is option B. 

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

Formation of ATP in respiration is called

  1. Photophosphorylation

  2. Substrate phosphorylation

  3. Oxidative phosphorylation

  4. Phosphorylation
Reveal answer Fill a bubble to check yourself
C 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 C. 

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

Oxidative phosphorylation of cytoplasmic $NADH (H^+)$ takes place in

  1. Cytosol

  2. E.R.

  3. Mitochondria

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

A large amount of NADH produced during glycolysis and Krebs cycle undergoes oxidation with phosphorylation of ADP to form ATP which is supported by mitochondrial electron transport assembly and ATP synthase which are integral protein complexes of the inner mitochondrial membrane. The electron transport assembly is comprised of a series of protein complexes that catalyze sequential oxidation-reduction reactions.

Thus, the correct answer is option C.

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

During carbohydrate metabolism, NADH is produced in which of the following locations?
I. Cytosol
II. Mitochondrial matrix
III. Nucleus.

  1. I only

  2. II only

  3. I and II only

  4. I, II and III
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In  the cytoplasm, one glucose molecule breaks down into two pyruvate molecules, and creates two NADH molecules by glycolysis. Transformation of one pyruvate from cytosol to one acetyl CoA produces one NADH molecule in the mitochondrial matrix. During  each turn of Krebs cycle, each acetyl CoA is systematically processed through the cycle and produces three NADH molecules.

So, the correct option is 'I and II only'. 

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

Oxidation of one molecule of glucose yields 38 mols of ATP in the proportion of

  1. 8 in cytosol and 30 in mitochondrion

  2. 30 in cytosol and 8 in mitochondrion

  3. 38 in cytosol

  4. 38 in mitochondrion
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
 Process  Site  Energy Release
 Glycolysis(breakdown of glucose into pyruvic acid)  In cytoplasm  2 ATP2 NADH
Decarboxylation(conversion of pyruvic acid into Acetyl co enzyme) mitochondria  2 ATP
 CItric Acid Cycle(Oxidation of acetyl co enzyme)(When cycle runs twice) mitochondria  8 NADH2 FADH2 GTP
 Total    10+28=38
So the correct option is "8 in cytosol and 30 in mitochondria".
Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

The role of mitochondria in oxidative phosphorylation was explained by 

  1. Leninger

  2. Embden

  3. Krebs

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

  • Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy which is used to produce ATP. In most eukaryotes, this takes place inside mitochondria. This was explained by Leininger
Thus, the correct answer is 'Leininger.'

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

In Kreb's cycle, how many oxidation (dehydrogenation) occur?

  1. 4

  2. 6

  3. 2

  4. 1
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In Kreb's cycle the oxidation or dehydrogenation reaction occurs 4 times as follows:

  1. Isocitrate to alpha-ketoglutarate (NADH is formed)
  2. alpha-ketoglutarate to succinyl co-A (NADH is formed)
  3. Succinate to Fumarate (FADH$ _{2}$ is formed)
  4. Malate to oxaloacetate (NADH is formed)
Hence, the correct answer is '4'.

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

Which is formed in oxidative phosphorylation?

  1. ATP in photosynthesis

  2. ATP in respiration
  3. $NADPH _2$ in photosynthesis
  4. $NADPH _2$ in respiration.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Oxidative phosphorylation-


This process takes place in mitochondria. In this process ATP is formed when electron are transferred from 

NADH or $FADH _2$ to $O _2$

(B) ATP in respiration occurs or is formed in oxidation phosphorylation.

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

Two copper centers are component of

  1. Cytochrome $bc _1$ complex

  2. NADH dehydrogenase complex

  3. ATP synthase complex

  4. Cytochrome c oxidase complex
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Option 'A' is correct.


Two copper centres two $W _a$ and $W _b$ are component of cytochrome $bc$, complex. $W _a$ contains two copper cone which are linked by two bridging cysteine residue, whereas $W _b$ is linked by there histidine residues.

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

Which of the following is a coenzyme?

  1. NAD

  2. NADP

  3. FAD

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

Co-enzymes are organic compounds, are bound to the the enzyme to make the enzyme catalytically active, but their association with the enzyme is only transient, usually occurring during the course of catalysis. Co-enzymes serve as co-factors in a number of different enzyme catalyzed reactions. The essential chemical components of many coenzymes are vitamins, e.g., coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain the vitamin niacin; flavin adenine dinucleotide (FAD) is derived from riboflavin vitamin.

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

All of the following is true about oxidative phosphorylation, except

  1. It occurs in the inner membrane of the mitochondrion.
  2. It involves O$ _2$ as the final electron acceptor.
  3. It produces 2 ATPs for each FADH$ _2$.

  4. It can occur under anaerobic conditions.

  5. It involves a proton gradient.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Oxidative phosphorylation is an ATP generating process, which takes place in the inner membrane of mitochondria of aerobic organisms. In a generic sense, this process generates ATP via transferring electrons from $FADH _2$ or NADH via a series of complex carriers. Oxygen is a vital constituent of this process for its role as the final electron acceptor. Therefore, oxidative phosphorylation cannot take place in absence of oxygen. Hence, the correct answer is (D).

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

Which of the following is produced by oxidative phosphorylation?

  1. Oxygen and water

  2. NADH and ATP

  3. Pyruvate and NADPH

  4. Water and ATP

  5. Oxygen and NADH
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The metabolic process of releasing energy from food can be termed as oxidative phosphorylation. It occurs in the mitochondria of eukaryotic cell. In this process, the electrons are transported through different carriers ultimately to the oxygen molecule. these electrons reduce oxygen to form water and release energy which converts ADP to ATP. 

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'