All Free Biology MCQs with Answers

3501. Which of the following is the end product of anaerobic respiration?

• A. Methyl alcohol
• B. Acetaldehyde
• C. Formaldehyde
• D. Ethyl alcohol

Explanation: Each pyruvic acid molecule produced during glycolysis is converted to ethyl alcohol in two steps. In the first step pyruvic acid is decarboxylated under the action of enzyme to produce acetaldehyde, a two carbon molecule. NADH+H+ reduces acetaldehyde to ethyl alcohol.CH3.CO.COOH → CH3.CHO + CO2CH3.CHO + NADH + H+ → CH3.CH2.OH + NAD+

3502. What's the importance of krebs's cycle?

• A. Production of amino acids
• B. Production of vitamins
• C. Production of ATP molecules through oxidative phosphorylation
• D. Production of pyruvic acid

Explanation: During steps 3, 4, and 8 of Krebs' cycle, 3 molecules of NADH + H+ are produced by oxidative decarboxylation of isocitrate, alpha-ketoglutarate, and malate, respectively. These NADH + H+ molecules are converted into ATP molecules by oxidative phosphorylation. Hence this option is correct.

3503. The acceptor of carbon dioxide in Calvin cycle Is:

• A. RuBP
• B. RuMP
• C. PGA
• D. PGAL

Explanation: Ribulose bisphosphate (RuBP) is generally referred to as CO2 acceptor because it is capable of combining with carbon dioxide with the help of Ribulose bisphosphate (RuBP) carboxylase/oxygenase also known as RuBisCO.

3504. Anaerobic respiration, compared to aerobic respiration, produces?

• A. More ATPs
• B. Less ATPs
• C. Equal ATPs
• D. Does not produce ATPs

Explanation: During anaerobic respiration, the pyruvic acid molecules are converted either to lactic acid or ethanol with the release of a very small amount of energy, i.e., just 2 ATPs.

3505. The final acceptor of both electrons & protons during light reactions of photosynthesis is:

• A. Pq
• B. Pc
• C. Fd
• D. NADP+

Explanation: NADP+ (Nicotinamide adenine dinucleotide phosphate) is the final electron and proton acceptor during the light reactions of photosynthesis.

3506. End product of Calvin cycle is:

• A. 3 phosphoglycerate
• B. 1-3 biphosphoglycerate
• C. Glyceraldehyde 3 phosphate
• D. Glucose

Explanation: The Calvin cycle, part of photosynthesis, generates G3P (glyceraldehyde 3-phosphate) from three carbon dioxide molecules using ATP and NADPH. It produces six G3P molecules, one of which is used to form carbohydrates like glucose, while five regenerate RuBP to keep the cycle going.

3507. The only copper containing protein involved during the light reactions of photosynthesis is

• A. Plastoquionone
• B. Cytochrome
• C. Ferridoxin
• D. Plastocyanin

Explanation: Plastocyanin is the copper-containing protein in light-dependent reaction ( Z scheme)

3508. Which is the major event in the electron transport chain?

• A. ATP synthesis
• B. Substitution
• C. Decarboxylation
• D. Isomerization

Explanation: The electron transport chain is responsible for the production of ATP through a process called oxidative phosphorylation. As electrons are passed along the chain, a proton gradient is established, and the energy released during this process is used to drive the synthesis of ATP from ADP and inorganic phosphate. This ATP synthesis is the primary purpose of the electron transport chain in cellular respiration. The other options listed (decarboxylation, isomerization, and substitution) are not the major events in the electron transport chain.

3509. Out of 36 ATPs, how many are produced in the electron transport chain?

• A. 28
• B. 30
• C. 32
• D. 34

Explanation: Out of the 36 ATPs that can potentially be generated through oxidative phosphorylation and the electron transport chain, approximately **32** ATPs are produced. The precise number can vary depending on specific factors and conditions, but 32 ATPs is a commonly cited estimate for the net ATP yield in eukaryotic cells during cellular respiration.

3510. The major enzyme involved in the transfer of the phosphate group from ATP to glucose is:

• A. Isomerase
• B. Dehydrogenase
• C. Kinase
• D. Decarboxylase

Explanation: The major enzymes involved in the transfer of a phosphate group from ATP to glucose are kinases (Option C). Specifically, the enzyme hexokinase is responsible for catalyzing this phosphorylation reaction, where a phosphate group is transferred from ATP to glucose to form glucose-6-phosphate.The other enzymes listed (isomerase, dehydrogenase, and decarboxylase) are involved in different types of biochemical reactions and are not responsible for this specific phosphorylation step in glucose metabolism.