All Free Biology MCQs with Answers

4101. In glycolysis, the six-carbon molecule is split into G-3-P and DAP, then DAP is also converted into G-3-P in step no. _.

• A. 2 & 3
• B. 3 & 4
• C. 4 & 5
• D. 5 & 6

Explanation: Fructose 1, 6 bisphosphate splits up into glyceroldehyde 3.phosphate and dihydroxyacetone phosphate during step no.4 of glycolysis which is followed by step no.5 in which dihydroxyacetone phosphate is also converted into glyceraldehyde three phosphate (G.3.P). See explanation of question # 27

4102. The step of glycolysis that involves removal of high energy phosphate by two ADP molecules to get two ATP molecules and two 3PGA molecules is:

• A. Step - 4
• B. Step - 6
• C. Step - 5
• D. Step - 7

Explanation: In step no. 7 of glycolysis, two molecules of 1, 3 bisphosphoglycerate are dephosphorylated, two molecules of ADP are phosphorylated to get two ATPs and as a result two molecules of 3PGA are formed.

4103. The oxidation - reduction substances which take part in respiratory chain are following EXCEPT:

• A. Coenzyme Q
• B. Molecular oxygen
• C. Cytochromes b, c, a and a3
• D. Cytochrome f

Explanation: Cytochrome f is a protein involved in photosynthesis and is not part of the respiratory chain. It functions as an electron carrier in the electron transport chain of photosystem I in photosynthetic organisms, such as cyanobacteria and algae.

4104. In respiratory electron transport chain, the first ATP is formed from ADP and inorganic phosphate, utilizing the free energy obtained by oxidation of :

• A. NADH
• B. FADH
• C. Coenzyme Q
• D. Cytochrome C

Explanation: It is first step of respiratory electron transport chain in which NADH is oxidized by coenzyme Q. This oxidation yields enough free energy to permit the synthesis of a molecule of ATP from ADP from ADP and inorganic phosphate.

4105. In respiratory electron transport chain coenzyme - Q is reduced by:

• A. NADH
• B. Cytochrome - C
• C. FADH
• D. Cytochrome - a

Explanation: As NADH stands at higher energy level and electron move from higher to lower energy level, thus NADH is oxidized and coenzymes Q is reduced.

4106. In respiratory electron transport chain cytochrome - b is reduced by:

• A. NADH
• B. FADH
• C. Cytochrome - C
• D. Coenzyme - Q

Explanation: Cytochrome-b is reduced by electrons which are released by the oxidation of coenzyme Q.

4107. In respiratory electron transport chain cytochrome - a is reduced by oxidation of:

• A. NADH
• B. FADH
• C. Cytochrome - C
• D. Coenzyme - Q

Explanation: Cytochrome-a is reduced by cytochrome c which is oxidized and electrons are used to reduced cytochrome a

4108. In respiratory electron transport chain, the third ATP is produced by the oxidation of:

• A. NADH
• B. Cytochrome - b
• C. Cytochrome - c
• D. Cytochrome - a3

Explanation: When cytochrome a3 is oxidized and O2 is reduced to form water, electrons release some free energy to come to the lower energy state and as a result ADP is phosphorylated into ATP by inorganic phosphate using that free energy.

4109. NADH + H+ + 3ADP + 3Pi + ½ O2 ⎯⎯→ 3NAD+ + H2O + 3ATP. The equation has summarized:

• A. Glycolysis
• B. Respiratory chain
• C. Kreb's cycle
• D. Photosynthetic electron transport chain

Explanation: This is summary equation of respiratory electron transport chain.

4110. Pumping of protons (H+) across the inner membrane of mitochondrion folded into cristae, between matrix of mitochondrion and mitochondrion's intermembrane space occur for chemiosmosis of:

• A. Oxidative phosphorylation
• B. Cyclic phosphorylation
• C. Photophosphorylation
• D. Non-cyclic phosphorylation

Explanation: The organelle (mitochondrion) clearly indicates it.