Lakshya Education MCQs

Question: In Kreb’s cycle ______.
Options:
A.ADP is converted to ATP
B.acetyl-CoA is converted to CO2 and H2O
C.glucose is converted in CO2
D.pyruvic acid is converted to ATP
Answer: Option B
: B

Kreb’s cycle, also known as tricarboxylic acid cycle is a process in whichthe glycolytic product - pyruvic acid is converted to CO2and H2O. Pyruvic acid enters Kreb's cycle as acetyl-CoA. Kreb's cycle takes place in the mitochondria.

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Question 1. Link enzyme in cellular respiration which catalyzes the substrate produced during glycolysis, and funnels it into the Kreb's cycle is ______.
  1.    Citrate synthetase
  2.    Pyruvate dehydrogenase
  3.    Isocitrate dehydrogenase
  4.    Succinyl thiokinase
Answer: Option B
: B

Pyruvic acid synthesized in glycolysis must enter inside the mitochondria, where oxidative decarboxylation occurs in the presence of NAD+and coenzyme-A. This results in the formation of acetyl CoA which can enter the Kreb's cycle. This reaction is catalyzed by pyruvate dehydrogenase.
Question 2. When one molecule of glucose is completely oxidised during aerobic respiration, how many molecules of carbon dioxide are released due to tricarboxylic acid cycle?
  1.    One
  2.    Two
  3.    Three
  4.    Four
Answer: Option D
: D

Six carbon dioxide molecules are released by complete oxidation of one glucose molecules. Two carbon dioxide molecules are released during oxidative decarboxylation reaction when the glycolytic products, that is two molecules of pyruvate areconverted into two molecules of acetyl CoA and channelled into the Kreb's cycle. And four carbondioxide molecules are released during theKreb’s cycle, during the breakdown of two molecules of isocitrate to alpha-ketoglutarate and the breakdown of alpha-ketoglutarates to succinyl CoA.
Question 3. The mechanism of ATP formation both in chloroplast and mitochondria is explained by ______.
  1.    Relay pump theory of Godlewski
  2.    Munch’s pressure/mass flow model
  3.    Chemiosmotic theory of Mitchell
  4.    Cholondy – Went’s model
Answer: Option C
: C

As per Peter Mitchell’s chemiosmotic – coupling hypothesis, outward pumping of protons across the inner chloroplast or mitochondrial membrane results in accumulation of protons between outer and inner membrane. A proton gradient is thus established. As protons now flow back passively down the gradient, the proton motive force is utilized to synthesize ATP.
Question 4. In Kreb’s cycle ______.
  1.    ADP is converted to ATP
  2.    acetyl-CoA is converted to CO2 and H2O
  3.    glucose is converted in CO2
  4.    pyruvic acid is converted to ATP
Answer: Option B
: B

Kreb’s cycle, also known as tricarboxylic acid cycle is a process in whichthe glycolytic product - pyruvic acid is converted to CO2and H2O. Pyruvic acid enters Kreb's cycle as acetyl-CoA. Kreb's cycle takes place in the mitochondria.
Question 5. Cyanide resistant pathway is _____.
  1.    Anaerobic respiration
  2.    Aerobic respiration
  3.    Both (a) and (b)
  4.    Krebs cycle
Answer: Option A
: A

Cyanide is a deadly poison of respiration and inhibit the activity of cytochrome –coxidase complex (which contains cytochromeaand cytochromea3) of the electron transport chain inaerobic respiration. Thus, no proton gradient will be established and no ATP will be formed. As the reoxidationof NADH and FADH2ceases, due to the blockageof the ETC, the availability of hydrogen acceptors like NAD+and FADfor Kreb’s cycle and glycolysis pathways also ceases. Thus stopping respiration. In anaerobic respiration the electron acceptors NAD+ and FADH2 can be regenerated anaerobically and therefore anaerobic respiration is a cyanide resistant pathway.
Question 6. Which of the following molecules is a product in respiration and substrate in photosynthesis?
  1.    O2
  2.    CO2
  3.    CO
  4.    N2
Answer: Option B
: B

CO2 is released during respiration and forms the product of respiration. Whereas in photosynthesis, the carbon dioxide molecule is fixed to form glucose. ThereforeCO2forms the substrate in photosynthesis.

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