Biology Questions and Answers – Aerobic Respiration – 1

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This set of Biology Multiple Choice Questions & Answers (MCQs) focuses on “Aerobic Respiration – 1”.

1. What is aerobic respiration?
a) Partial oxidation of glucose
b) Incomplete oxidation of glucose
c) Complete oxidation of organic substances
d) Complete oxidation of only glucose
View Answer

Answer: c
Explanation: Aerobic respiration is the complete oxidation of organic substances which occur in the presence of oxygen. It is an energy yielding process as a large amount of energy in the form of ATP is released. Water and carbon dioxide are also released as its by-products.
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2. Where does aerobic respiration usually takes place?
a) Lower vertebrates
b) Higher organisms
c) Prokaryotes
d) Only unicellular eukaryotes
View Answer

Answer: b
Explanation: Aerobic respiration is most common in higher organisms. In eukaryotes, the steps of aerobic respiration take place within the mitochondria and this requires oxygen.

3. What is the efficiency of aerobic respiration?
a) More than 75%
b) Approximately 45%
c) Less than 20%
d) 99%
View Answer

Answer: b
Explanation: The efficiency of aerobic respiration is approximately 45%. For aerobic respiration, the final product of glycolysis is transported from the cytoplasm into the mitochondria.
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4. Where does the second process of aerobic respiration take place?
a) In the lumen of mitochondria
b) In the matrix of mitochondria
c) In the inner membrane of mitochondria
d) In the cristae of mitochondria
View Answer

Answer: c
Explanation: The two stages of aerobic respiration are Kreb’s cycle and electron transport system. The first process takes place in the matric of mitochondria while the second process takes place in the inner membrane of mitochondria in eukaryotes.

5. How many CO2 molecules are left during the complete oxidation of pyruvate?
a) One
b) Two
c) Five
d) Three
View Answer

Answer: d
Explanation: The complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms takes place while leaving three molecules of Carbon-dioxide.
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6. Which of the following is a crucial event in aerobic respiration?
a) Simultaneous synthesis of ATP
b) Synthesis of ethanol and water
c) Complete oxidation of methanol
d) Complete oxidation of carbon-dioxide
View Answer

Answer: a
Explanation: The crucial events in aerobic respiration are the complete oxidation of pyruvate and the passing on of the electrons removed as a part of the hydrogen atoms to molecular oxygen with the simultaneous synthesis of ATP.

7. After entering the mitochondrial matrix, pyruvate undergoes reductive decarboxylation.
a) True
b) False
View Answer

Answer: b
Explanation: Pyruvate is the product of glycolysis which occurs in the cytoplasm of all the living organisms. Therefore, for pyruvate to enter Kreb’s cycle, it enters in the mitochondrial matrix where it undergoes oxidative decarboxylation as from 2 molecules of pyruvate, 6 molecules of carbon dioxide are released.
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8. Which of the following participates in the reaction catalysed by pyruvic dehydrogenase?
a) Carbon dioxide
b) Water
c) Ethanol
d) Coenzyme A
View Answer

Answer: d
Explanation: The reaction catalysed by pyruvic dehydrogenase requires the participation of several coenzymes that include NAD+ and Coenzyme A.

9. How many molecules of NADH are produced by the metabolism of pyruvic acid?
a) One
b) Two
c) Three
d) Four
View Answer

Answer: b
Explanation: During the process, two molecules of NADH are produced from the metabolism of two molecules of pyruvic acid i.e. produced from one glucose molecule during glycolysis.
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10. Who discovered the Tricarboxylic acid cycle?
a) Hans Krebs
b) Ernst Haeckel
c) Louis Pasteur
d) Charles Darwin
View Answer

Answer: a
Explanation: Tricarboxylic acid cycle, more commonly known as Kreb’s cycle was elucidated by Hans Krebs who first discovered it in the flight muscles of pigeon.

11. The TCA cycle starts with the condensation of which of the following compounds?
a) Sucrose
b) Acetyl group
c) Ethanol
d) Pyruvate
View Answer

Answer: b
Explanation: The TCA cycle starts with the condensation of acetyl group. It reacts with oxaloacetic acid and water and forms citric acid. This reaction is catalysed by the enzyme citrate synthase and a molecule of CoA is released. Further, citrate is isomerised to isocitrate with the help of isomerase enzyme.

12. After the condensation of an acetyl group, citrate is replaced by malic acid.
a) True
b) False
View Answer

Answer: b
Explanation: After the condensation of acetyl group with oxaloacetic acid, citric acid is formed. This citrate then isomerises to isocitrate. It then leads to the formation of α-ketoglutaric acid.

13. How many steps of decarboxylation lead to the formation of ketoglutaric acid?
a) One
b) Three
c) Two
d) Seven
View Answer

Answer: c
Explanation: Two steps of decarboxylation leads to the formation of ketoglutaric acid. When citric acid is formed in the cycle, it then forms cis-acotinic acid and then isocitric acid. Isocitric acid further forms oxalosuccinic acid which finally forms ketoglutaric acid in the presence of oxalosuccinate decarboxylase enzyme.

14. Which of the following compounds is the first member of the TCA cycle?
a) Oxaloacetic acid
b) α-ketoglutaric acid
c) Succinic acid
d) Malic acid
View Answer

Answer: a
Explanation: Oxaloacetic acid is the first member of the TCA cycle. The continued oxidation of acetyl CoA via the TCA cycle requires the continued replenishment of Oxaloacetic acid.

15. What is the full form of SLP?
a) Subgeneric Level of Phosphorylation
b) Subcutaneous Level Photophosphorylation
c) Substrate Level Phosphorylation
d) Substrate Level Pyruvatisation
View Answer

Answer: c
Explanation: SLP stands for Substrate Level Phosphorylation. During the conversion of succinyl-CoA to succinic acid, a molecule of GTP is synthesised. This is substrate-level phosphorylation.

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