All Free Biology MCQs with Answers

4001. Number of ATP molecules used during preparatory phase of glycolysis:

• A. 2
• B. 4
• C. 1
• D. 6

Explanation: Glycolysis comprises of two phases in 1st half, Glucose is converted into two 3 carbon compounds known as glyceraldehyde phosphate using 2 molecules of ATP in step wise reactions.

4002. Water is released during conversion of:

• A. 2-phosphoglycerate → PEP
• B. 3-phosphoglycerate → 2-phosphoglycerate
• C. 1,3 bisphosphoglycerate → 3-phosphoglycerate
• D. G3P → 1,3 bisphosphoglycerate
• E. None of these

Explanation: Water is released during conversion of 2-phosphoglycerate to phosphoenolpyruvate. So, A is correct option.

4003. Which one of the following represents de-phosphorylation?

• A. Fructose I-phosphate → Fructose 1,6-biphosphate
• B. Fructose 1 ,3 bisphosphoglyeerate → 3 phosphoglycerate
• C. Fructose I-phosphate → Fructose 6-phosphate
• D. Glucose 6-phosphate → Fructose 1-phosphate

Explanation: Removal of phosphate group from a molecule is called de-phosphorylation. Conversion of fructose 1 ,3-bisphosphoglycerate into 3-phosphoglycerate is a de-phosphorylation reaction.

4004. When products of glycolysis pass through Krebs cycle, it will produce:

• A. 2 NADH, 2 FADH2, 2 ATP
• B. 1 NADH, 1 FADH2, 1 ATP
• C. 1 NADH, 3 FADH2, 2 ATP
• D. 6 NADH, 2 FADH2, 2 ATP

Explanation: When products of glycolysis pass through Krebs cycle it will produce 6 molecules of NADH. 2 molecules of FADH2 and 2 molecules of ATP.

4005. The precursor of fumarate during Krebs cycle require _ for fumarate synthesis.

• A. Amino acid aspartate
• B. Fumarate dehydrogenase
• C. Succinate dehydrogenase
• D. FAD+ Oxidase

Explanation: Therefore, amino acid aspartate is required as a precursor for the synthesis of fumarate in the Krebs cycle.

4006. Before pyruvate enters the citric acid cycle, it is de carboxylated, oxidized and combined with coenzyme A, forming acetyl CoA, carbon dioxide and one molecule of:

• A. NADH
• B. FADH2
• C. ATP
• D. ADP

Explanation: Before pyruvate enters the citric acid cycle, it is decarboxylated, oxidized, and combined with coenzyme A, forming acetyl CoA, carbon dioxide, and one molecule of NADH.

4007. Which of the following process is used in the conversion of pyruvate to acetyl CoA?

• A. Decarboxylation
• B. Dehydration
• C. Dehydrogenation
• D. Both A and C

Explanation: When pyruvate molecule is converted into acetyl CoA, one carbon ofpyruvate is removed in the form of carbon dioxide (decarboxylation) along with hydrogen (dehydrogenation) that is added to NADH.

4008. Biological oxidation involves removal of hydrogen, linked with specific coenzymes and is catalyzed by:

• A. Carboxylase
• B. Hydrogenase
• C. Dehydrogenase
• D. Catalase

Explanation: Biological oxidation involves the removal of hydrogen. a redox reaction catalyzed by the dehydrogenases, linked to a specific coenzyme.

4009. Before entering Krebs cycle, the pyruvate decarboxylated into:

• A. a-kerogluteric acid
• B. Glyceric acid
• C. Citirc acid
• D. Acetaldehyde

Explanation: Glycolysis results in pyruvate fonnation. It enters mitochondria where an enzyme pyruvatc decarboxylase removes carbon dioxide from it. This decarboxylation results in formation of acetic acid.

4010. During respirartory chain of cellular respiration, cytochrome c oxidizes:

• A. Cytochrome a
• B. Cytochrome b
• C. Cytochrome a3
• D. Cytochrome a complex

Explanation: In electron- transport chain electrons moves through proteins named as electron carriers. Coenzyme Q reduces cytochrome b and then electrons are passed on to cytochrome c resulting in oxidation of cytochrome b.