All Free Biology MCQs with Answers

4111. Glycolysis is inhibited by inhibition of phosphofructokinase through feedback mechanism by accumulation of _ in mitochondrion.

• A. Citrate
• B. Oxaloacetate
• C. Succinate
• D. Adenosine triphosphate

Explanation: Citrate is a key molecule in cellular metabolism, playing a central role in both glycolysis and the citric acid cycle (also known as the Krebs cycle or tricarboxylic acid cycle).In the citric acid cycle, citrate is formed when acetyl-CoA combines with oxaloacetate.

4112. The condition in which reduced metabolic products comprising the "dept" accumulate due to inability of oxidative metabolism to function rapidly enough. The "debt" is payed off when the metabolism that produces reduced products slows. This is called:

• A. Electron debt
• B. Oxygen debt
• C. Hydrogen debt
• D. Carbon debt

Explanation: It have been taken from glossary of text book of biology book-I. It is definition of oxygen debt.

4113. The hydrogen ions move down their gradient from thylakoid space to outside through special complexes found in thylakoid membrane called:

• A. Ferredoxin
• B. ATP synthase
• C. Cytochrome complex
• D. Plastoquinone

Explanation: ATP synthase is an important enzyme that creates the energy storage molecules adenosine triphosphate (ATP). ATP is the most commonly used "energy currency" of cells from mostorganisms.

4114. In which of the following reactions of glycolysis, oxidation takes place?

• A. Glucose 6-PO4 to fructose 6-PO4
• B. Glyceraldehyde 3 - phosphate to 1, 3 - bisphosphoglycerate
• C. 1. 3 - bisphosphoglycerate to 3 - phosphoglycerate
• D. 2 - phosphoglycerate to phosphoenol pyruvate

Explanation: Oxidation is the loss of electrons by an atom or molecule. In glycolysis, there are two main reactions that involve oxidation:Phosphoglyceraldehyde oxidation: In this reaction, glyceraldehyde-3-phosphate is oxidized to 1,3-bisphosphoglycerate. This reaction is catalyzed by the enzyme glyceraldehyde-3-phosphate dehydrogenase. In the reaction, glyceraldehyde-3-phosphate loses a hydrogen atom, which is accepted by NAD+ to form NADH.Pyruvate oxidation: In this reaction, pyruvate is oxidized to acetyl-CoA. This reaction is catalyzed by the enzyme pyruvate dehydrogenase complex. In the reaction, pyruvate loses a carbon dioxide molecule and a hydrogen atom, which are accepted by NAD+ to form NADH and CO2.

4115. In the Krebs cycle, the FAD electron transport system operates during the conversion of:

• A. Succinyl CoA to succinic acid.
• B. α - ketoglutarate to succinyl CoA
• C. Succinic acid to fumaric acid
• D. Fumaric acid to malic acid

Explanation: The FAD electron transport system operates during the conversion of succinate to fumarate in the Krebs cycle.The Krebs cycle, also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle, is a series of chemical reactions that are used by all aerobic organisms to generate energy. The Krebs cycle takes place in the mitochondria of cells.

4116. How many ATP and NADPH2 are required for synthesis of one mole of glucose?

• A. 12ATP and 12NADPH2
• B. 12ATP and 18NADPH
• C. 18ATP and 12NADPH2
• D. 9ATP and 6NADPH

Explanation: The synthesis of one mole of glucose from carbon dioxide and water in the Calvin cycle requires 18 ATP and 12 NADPH.

4117. The molecular mechanism of oxidative phosphorylation takes place in conjunction with respiratory chain in the:

• A. Outer membrane of mitochondrion
• B. Inner membrane of mitochondrion
• C. Matrix of mitochondrion
• D. Inner side of thylakoid membrane

Explanation: The molecular mechanism of oxidative phosphorylation takes place in conjunction with the respiratory chain in the mitochondrial inner membrane.The respiratory chain is a series of protein complexes that are embedded in the mitochondrial inner membrane. The respiratory chain uses the energy released from the oxidation of NADH and FADH2 to pump protons across the mitochondrial inner membrane. This creates a proton gradient, which is used to drive the synthesis of ATP.

4118. The process that uses membranes to couple redox reaction to ATP production:

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

Explanation: The process that uses membranes to couple redox reactions to ATP production is called chemiosmosis.Chemiosmosis is a process that occurs in the mitochondria of cells. It is a series of reactions that use the energy released from the oxidation of NADH and FADH2 to pump protons across the mitochondrial inner membrane. This creates a proton gradient, which is used to drive the synthesis of ATP.

4119. How many electrons flow from single molecule of H2O to reduce NADP?

• A. 2
• B. 3
• C. 4
• D. 5

Explanation: Two electrons flow from a single molecule of H2O to reduce NADP+ in non-cyclic photophosphorylation.

4120. What is a copper containing protein?

• A. Cytochrome
• B. Plastoquinone
• C. Plastocyanin
• D. Ferredoxin

Explanation: Plastocyanin is a copper-containing protein that is found in the thylakoid membranes of chloroplasts. It is a blue protein that helps to transfer electrons from Photosystem II to Photosystem I in the light-dependent reactions of photosynthesis.