All Free Biology MCQs with Answers

4131. One molecule of FADH2 is produced in Krebs cycle during conversion of:

• A. Fumarate to malate
• B. Succinate to fumarate
• C. Malate to oxaloacetate
• D. Alpha Ketoglutarate to succinate

Explanation: Only one molecule of FADH2 is produced in the Krebs cycle during the conversion of succinate to fumarate.FADH2 is a reduced form of flavin adenine dinucleotide (FAD). It is produced when FAD is oxidized by the enzyme succinate dehydrogenase. Succinate dehydrogenase is a membrane-bound enzyme that is located in the inner mitochondrial membrane.The oxidation of succinate to fumarate by succinate dehydrogenase releases two electrons. These electrons are then transferred to FAD, which is reduced to FADH2.FADH2 can then enter the electron transport chain and be used to produce ATP. However, it produces fewer ATP molecules than NADH. For every molecule of FADH2 that is oxidized, only 2 protons are pumped across the inner mitochondrial membrane. This creates enough energy to synthesize 2 ATP molecules.

4132. Final acceptor of electron in respiratory chain is:

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

Explanation: The final acceptor of electrons in the respiratory chain is oxygen. Oxygen is a highly electronegative molecule, which means that it has a strong affinity for electrons. This affinity for electrons is what allows oxygen to accept electrons from the electron transport chain and to be reduced to water.

4133. Which one of the following molecules of respiratory chain is found at the lowest energy level?

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

Explanation: Cytochrome a3, also known as cytochrome c oxidase or Complex IV, is a crucial enzyme in the electron transport chain of cellular respiration. This enzyme plays a central role in the process of oxidative phosphorylation, where electrons are transferred through a series of protein complexes, ultimately leading to the production of adenosine triphosphate (ATP), the cell's primary energy currency.

4134. NADP+ reductase accept electron from?

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

Explanation: Ferredoxin is a small iron-sulfur protein that acts as an electron carrier in photosynthetic organisms.Ferredoxin receives electrons from PSI and transfers them to ferredoxin-NADP+ reductase, which catalyzes the reduction of NADP+ to NADPH. This step is crucial for the production of NADPH, which is used in the Calvin cycle for carbon fixation.

4135. Common step of aerobic and anaerobic respiration is:

• A. Glycolysis
• B. Pyruvic acid oxidation
• C. Krebs cycle
• D. Respiratory chain

Explanation: "The explanation for this question will be added soon!".

4136. At which numbered stages does decarboxylation take place?

• A. 1 and 2
• B. 1,2 and 3
• C. 1,3 and 4
• D. 1,2,3 and 4

Explanation: At stage 1,2 and 3, decarboxylation take place.

4137. Where are the enzymes located which are involved in the chemical reactions which occur during glycolysis?

• A. In the fluid matrix of cytoplasm
• B. In the mitochondria! matrix
• C. In the nuclear sap
• D. On the cristae of a mitochondrion

Explanation: Enzymes located in the fluid matrix of cytoplasm are involved in the chemical reactions which occur during glycolysis.

4138. Photosynthesis consists of emsentitilly two biological reaction systems, one following the other. The second of these systems does which of the following?

• A. Fixes carbon dioxide
• B. Works only in the presence of light
• C. Traps light energy
• D. Synthesis of ATP

Explanation: The second of these systems fixes carbon dioxide.

4139. The final acceptor of electron during non-cyclic electron pathway is:

• A. PS I
• B. PS II
• C. ATP
• D. NADP+

Explanation: The final acceptor of electron during non-cyclic electron pathway is NADP+ .

4140. During light reaction of photosynthesis ,which of the following phenomenon observed during cyclic phosphorylation as well as noncyclic phosphorylation?

• A. Formation of ATP
• B. Involvement of both PSI and PSI I pigment systems
• C. Release of NADPH
• D. Release of O2

Explanation: This option is incorrect, as formation of ATP is observed during cyclic phosphorylation as well as noncyclic phosphorylation.