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

Biological phosphorylation is the formation of 

  1. $N _{2}$
  2. $CO _{2}$
  3. $ATP$
  4. $SO _{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Biological phosphorylation is of two types- protein phosphorylation and oxidative phosphorylation. In protein phosphorylation, the proteins get attached with a phosphate group. 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.

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

$FAD^+$ is reduced during conversion of 

  1. Citric acid to isocitric acid
  2. Isocitric acid to $ \alpha - $ ketoglutaric acid
  3. $ \alpha - $ ketoglutaric acid to succinyl CoA

  4. Succinic acid to fumaric acid
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

During one of the steps of Krebs cycle, succinic acid is converted to fumaric acid. The reaction is accompanied by coenzyme FAD (flavin adenine nucleotide). This oxidation reaction liberates less free energy as compared to other oxidation reactions. FAD$^+$ is the hydrogen acceptor in this reaction as there is very less free-energy change. In this reaction, succinic acid is oxidized to fumaric acid. At the same time, FAD$^+$ is reduced to FADH$ _2$. 

Thus, the correct answer is option D.

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

Choose the correct answers from the alternatives given :
Substrate-level phosphorylation takes place in 

  1. Krebs cycle and the transition reaction

  2. glycolysis and the electron transport system

  3. electron transport system and the transition reaction

  4. glycolysis and the Krebs cycle
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Substrate level phosphorylation is the reaction where ATP is formed by the phosphate molecule that is taken from the substrate in the reaction.
  • In glycolysis during the conversion of 1,3 bisphosphoglyceric acid to 3 phosphoglyceric acid and coversion of phosphophenol to pyruvic acid; one molecule of ATP is formed during each reaction.
  • In kerb cycle during the formation of succinic acid from succinyl CoA GTP is formed which is a substrate level phosphorylation, afterwards this GTP is converted to ATP in a coupled reaction.
  • No substrate level phosphorylation takes place in oxidative phosphorylation or ETS
  • Therefore the answer 'glycolysis and the Krebs cycle' is correct.
Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Choose the correct answers from the alternatives given :
Which of the following occurs only in aerobic conditions?

  1. Glycolysis

  2. Lactate respiration

  3. Oxidative phosphorylation

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

  • Glycolysis is the first part of the reaction that provides substrate for the further reaction of aerobic and anaerobic reaction. IT takes place in cytoplasm and does not require any oxygen.
  • LActate respiration and fermentation both are the reaction that take place in the cells or the tissues which respiration in anaerobic conditions or when there is not enough oxygen.
  • Oxidative phosphorylation is the process that takes place in the in the inner mitochondrial membrane where the electrons and hydronium ions are transported through a series of complexs and at the end the electrons and hydronium are accepted by the oxygen and water is formed, this is the process in the aerobic respiration where the oxygen is used and it cannot be completed with it.
  • Therefore the answer option 'Oxidative phosphorylation' is correct.







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

Choose the correct answers from the alternatives given :
The direct energy source that drives ATP synthesis during oxidative phosphorylation is 

  1. a difference of $^H+$ concentration on opposite sides of the inner mitochondrial membrane

  2. the affinity of oxygen for electrons

  3. oxidation of glucose and other organic compounds

  4. endergonic flow of electrons down the electron transport chain
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • In mitochondria the ETS is used for the transport of electrons and hydronium ions from inner mitochondrial membrane to the inter membrane matrix of mitochondria.
  • Due to this the concentration of hydronium ions increases in the intermembrane matrix.
  • The ATP synthase complex which is present in the inner membrane of the mitochrondria are used for the synthesis of ATP.
  • The complex is used to transport hydronium ions from the intermembrane matrix down its concentration gradient
  • For every 2 hydronium ions transported through the complex one molecule of ATP is generated.
  • Therefore the transport of the H+ ions due the difference in the concentration provides direct energy for the formation of ATP.
  • Therefore the correct answer is option 'a difference of H+ concentration on opposite sides of the inner mitochondrial membrane'.









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

Choose the correct answers from the alternatives given :
The final electron acceptor of the electron transport chain that functions in oxidative phosphorylation 

  1. pyruvic acid

  2. oxygen

  3. water
  4. $NAD^+$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • Electrons that are transported through the ETS are passed through various complexs of the transport chain such as complex I, cytochrome c cytochrome b, etc
  • When the electrons are passed through the complexs one after the other hydrogen ions are also passed through along with it.
  • After the electrons and the hydrogen have passed through the last of the complex the last acceptor of the electron in this chain will be a molecule of oxygen after reacting to which a molecule of water is formed.
  • Therefore the correct answer is option 'oxygen'.








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

Choose the correct answers from the alternatives given :
Most of the ATP made during cellular respiration is generated by 

  1. direct synthesis of ATP by the Krebs cycle

  2. substrate-level phosphorylation

  3. oxidative phosphorylation

  4. glycolysis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  • Oxidation phosphorylation is the process where the electron acceptor such as NADH and FADH release their H ions and the ions and the electrons are tranported through various complexs of electron transport system.
  • NADH gives electrons which pass through 5 complexs of the ETS and FADH pass through 4 complexs of the ETS 
  • These electron at the end of the transport system react with oxygen and form a molecule of water.
  • Where the proton which is released by the complexs of the ETS during the transport of electrons are used in formation of ATP.
  • one molecule of NADH forms 3 molecules of ATP and one molecule of FADH forms 2 molecules of ATP
  • So after one cycle of kerb 4 molecules of NADH are released and one molecule of FADH which results in formation of 12 ATP and 2 ATP respectively. Thus generating 14 ATP for each pyruvic acid.
  • Therefore the amount of the maximum generated ATP in cellular respiration is done by oxidative phosphorylation.
  • Therefore the answer option 'oxidative phosphorylation' is correct.
Multiple choice bio-chemistry biological oxidation oxidative phosphorylation living organisms and energy production glycolysis

Which one is not correct for oxidation of food?

  1. It is multiple process

  2. All released energy is traped in form of ATP

  3. Traped energy is further used for bio synthesis of other molecules

  4. Oxidisable compound is known as respiratory substrate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

During the oxidation of carbon atoms from complex organic food molecule, carbon dioxide is released as a waste product. The energy released from these reactions is not used up by the cells completely. Alternatively, it is converted into ATP and NADH, and this can be used throughout the cell to power metabolism and construct new cellular components. In addition, workhorse proteins called enzymes use this chemical energy to catalyze chemical reactions within the cell.

So, the correct option is 'All released energy is trapped in form of ATP'.

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

During oxidative phosphorylation, proton return to

  1. Matrix from outside

  2. Outside from matrix

  3. In both directiion

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

Oxidative phosphorylation is the process of formation of ATP (energy) molecules inside the plant and animal cells. It takes place inside the mitochondria. During the oxidative phosphorylation, electrons flow from NADH  or FADH to O2 through the four different type complexes found in the inner mitochondrial membrane, which leads the pumping of the proton from outside to the matrix.

So, the correct answer is ' Matrix from outside '

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

Correct answer(w.r.t. ETS and oxidative phosphorylation in mitochondria):
(i) $F _1$ headpiece is a peripheral membrane complex and contains site of ATP synthesis
(ii) Passage of electrons through channel is coupled to catalytic site of $F _0$ component for ATP production.
(iii) $F _0$ is integral membrane protein  complex that forms the channel through which protons cross inner membrane
(iv) Cyt c is small protein attached to inner surface of inner mitochondrial membrane.
*

  1. (i) and (iii) are correct

  2. (ii) and (iii) are incorrect

  3. (iii) and (iv) are correct

  4. (i) and (i)v are incorrect
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

F1 is the peripheral complex for ATP synthesis, and F0 is the integral membrane protein forming the proton channel. Statements (i) and (iii) are correct.

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

In case NADH is oxidised in a single step to form water.

  1. Cell will burn

  2. Most of energy is liberated as heat
  3. $3$ ATP are formed
  4. $5$ ATP are formed
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

NADH is reoxidized in a single step to form water (in the presence of oxygen). NADH to donate electrons directly to Oxygen to water. NADH to Oxygen the many-electron carriers in the electron transport chain and heat is liberated as most of the energy.

So the correct answer is 'Most of the energy is liberated as heat'.

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

The function of ATP synthase enzyme is that

  1. It uses energy to move ions against their concentration gradient by removing a phosphate group from ATP.

  2. It uses the power of ions moving against their concentration gradient to add a phosphate group to ADP.

  3. It uses the power of ions moving down their concentration gradient to add a phosphate group to ADP.

  4. It uses the power of ions moving against their concentration gradient to remove a phosphate group from ATP.

  5. It uses the power of ions moving down their concentration gradient to remove a phosphate group from ATP.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Electron transport chain includes the downhill flow of electrons to final electron acceptor through a chain of membrane-bound carriers to facilitate the uphill transport of protons across a proton-impermeable membrane. It produces proton gradient that drives transport of protons (ions) down the concentration gradient through Fo particles of ATP synthase. The proton-motive force that drives movement of protons (ions) provides the energy for ADP phosphorylation. Thus, the correct answer is option C.

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

NAD of Krebs cycle functions as

  1. Acceptor of hydrogen ion and electrons

  2. Oxygen acceptor

  3. Oxygen donor

  4. Donor of phosphate ions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

NAD is a coenzyme which acts as an electron acceptor in Krebs cycle and acquires hydrogen ions to become NADH.

So the correct option is 'Acceptor of hydrogen ion and electrons'.