All Free Biology MCQs with Answers

3141. Electrons from NADH accepted by oxygen form how many ATPs?

• A. 1
• B. 3
• C. 4
• D. 2

Explanation: In the electron transport chain, each NADH donates electrons that ultimately reduce oxygen to water. During this process, enough energy is released to produce approximately 3 molecules of ATP through oxidative phosphorylation.

3142. What is the end product of glycolysis that does not enter the Krebs cycle directly?

• A. Acetic acid
• B. Alpha-ketoglutarate
• C. Pyruvic acid
• D. Citrate

Explanation: Pyruvic acid is the primary end product of glycolysis. It must be converted into acetyl-CoA before it can enter the Krebs cycle.

3143. In which body component does lactic acid fermentation take place?

• A. Brain
• B. Heart
• C. Liver
• D. Muscles

Explanation: During intense exercise, when oxygen level is insufficient, lactic acid fermentation occurs in skeletal muscles, leading to the accumulation of lactic acid and resulting in muscle fatigue.

3144. The final acceptor of electrons in the respiratory chain is

• A. NADH
• B. Cytochrome a3
• C. Water
• D. Oxygen

Explanation: Oxygen is the final electron acceptor in the electron transport chain, forming water after accepting electrons.

3145. Enzymes for oxidative phosphorylation are present on:

• A. Cristae
• B. Inner compartment
• C. Outer compartment
• D. Outer membrane

Explanation: The cristae are the folded structures of the inner mitochondrial membrane where oxidative phosphorylation takes place. These folds maximize the surface area available for housing the enzymes and protein complexes involved in the electron transport chain and ATP synthesis.

3146. Which one of the following is the universal hydrogen acceptor?

• A. ATP
• B. FMN
• C. CoA
• D. NAD

Explanation: NAD is the universal hydrogen acceptor, crucial in redox reactions. It accepts electrons and a proton to form NADH, which then participates in energy transfer during processes like glycolysis and the electron transport chain.

3147. To a living organism which of the following has the greater amount of available energy per molecule?

• A. NAD
• B. ATP
• C. ADP
• D. CO2

Explanation: ATP (Adenosine Triphosphate) is the primary energy currency of the cell, storing and providing energy for a variety of cellular activities. It releases energy when its phosphate bonds are broken.

3148. Synthesis of ATP in mitochondria requires:

• A. NADP
• B. Oxygen
• C. FMN
• D. ATP

Explanation: Oxygen serves as the final electron acceptor in the electron transport chain, accepting electrons from the chain and forming water. This process, known as oxidative phosphorylation, creates a proton gradient across the inner mitochondrial membrane, which is crucial for the generation of ATP through chemiosmosis.

3149. Which of the following makes direct use of oxygen?

• A. Glycolysis
• B. Krebs or citric acid cycle
• C. Electron transport chain
• D. Fermentation

Explanation: The electron transport chain occurs in the inner mitochondrial membrane and directly uses oxygen. Oxygen serves as the final electron acceptor in the electron transport chain, accepting electrons and forming water. This proton gradient drives ATP synthesis through oxidative phosphorylation.

3150. Organelles that are regarded as the "powerhouse" of the cell and in which the oxidative reactions of the respiratory process take place are:

• A. Chloroplasts
• B. Endoplasmic reticulum
• C. Mitochondria
• D. Lysosomes

Explanation: Mitochondria are often referred to as the "powerhouse" of the cell because they are the site of oxidative phosphorylation, where the majority of ATP is produced through the electron transport chain and ATP synthase during cellular respiration.