All Free Biology MCQs with Answers

4121. How many CO2 molecules are inserted into one Calvin cycle per RUBP:

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: Three CO2 molecules enter Calvin cycle per 3 RUBP molecules. to generate one molecule of carbohydrates. So for one RUBP molecule one CO2 molecule would be inserted.

4122. Most abundant protein on earth:

• A. Cellulose
• B. Rubisco
• C. Actin
• D. Myosin

Explanation: The most abundant protein on Earth is RuBisCO, which stands for Ribulose-1,5-bisphosphate carboxylase/oxygenase. It is an enzyme that is found in all photosynthetic organisms, including plants, algae, and cyanobacteria. RuBisCO is responsible for the fixation of carbon dioxide into glucose during photosynthesis.

4123. Cytochromes are electron transport intermediates containing Haem related:

• A. Coenzymes
• B. Prosthetic group
• C. Activator
• D. Ribozyme

Explanation: Cytochromes are electron transport intermediates that contain heme as a prosthetic group. A prosthetic group is an organic or inorganic non-protein part of an enzyme that is essential for its activity. Heme is a prosthetic group that is found in many different proteins, including cytochromes.

4124. C3 H6 O3 is:

• A. Pyruvic acid
• B. Lactic acid
• C. Ethyl alcohol
• D. Acetyl CoA

Explanation: C3H6O3 is the chemical formula for lactic acid.

4125. In which movement of electrons energy is released to yield an ATP:

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: When electrons move from cytochrome b to cytochrome c, they release a small amount of energy. This energy is not enough to make an ATP molecule. However, it is enough to help the ETC pump protons across the inner mitochondrial membrane. This creates a proton gradient, which is used to make ATP molecules later on.So, the movement of electrons from cytochrome b to cytochrome c is an important step in the ETC, even though it doesn't directly make ATP. It helps to create the conditions that are necessary for ATP synthesis to happen.

4126. Oxidative phosphorylation, synthesis of ATP in presence of oxygen occurs in:

• A. All types of cells
• B. All anaerobic cells
• C. All primitive cells
• D. All aerobic cell

Explanation: Oxidative phosphorylation, the synthesis of ATP in the presence of oxygen, occurs in all aerobic cells. Aerobic cells are cells that require oxygen to survive. They use oxidative phosphorylation to generate most of their ATP, which is the main source of energy for cellular processes.

4127. Before entering into Krebs cycle, the pyruvate is first decarboxylated and oxidized into:

• A. Alpha ketoglutaric acid
• B. Citric acid
• C. Glyceric acid
• D. Acetic acid

Explanation: Before entering the Krebs cycle, pyruvate is first decarboxylated and oxidized into acetyl-CoA. Acetyl-CoA is a two-carbon molecule that is the starting point for the Krebs cycle.The decarboxylation of pyruvate is a reaction that removes a carbon dioxide molecule from pyruvate. This reaction is catalyzed by the pyruvate dehydrogenase complex, which is an enzyme complex that is found in the mitochondrial matrix.The oxidation of pyruvate is a reaction that removes two electrons from pyruvate. These electrons are transferred to NAD+, which is reduced to NADH.

4128. Z-scheme is:

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

Explanation: The Z-scheme is a graphical representation of the electron transport pathway in non-cyclic photophosphorylation. It is called the Z-scheme because the pathway resembles the letter Z.The Z-scheme shows the movement of electrons from water to NADP+, with the help of a series of electron carriers. As the electrons move down the pathway, they release energy, which is used to pump protons across the inner mitochondrial membrane. This creates a proton gradient, which drives the synthesis of ATP by the enzyme ATP synthase.

4129. The product(s) of cyclic phosphorylation is/are:

• A. ATP
• B. NADP
• C. NADP and ATP
• D. NADP, ATP and oxygen

Explanation: The product(s) of cyclic phosphorylation are ATP only.Cyclic phosphorylation is a process that occurs in the chloroplasts of plants. It is a type of photophosphorylation, which means that it uses light energy to produce ATP. However, cyclic phosphorylation does not produce NADPH, which is a different molecule that is also produced by photophosphorylation.The process of cyclic phosphorylation begins with the absorption of light energy by chlorophyll molecules in the thylakoid membrane. This energy is used to pump protons across the thylakoid membrane, creating a proton gradient. The proton gradient is then used to drive the synthesis of ATP by the enzyme ATP synthase.No electrons are transferred to NADP+ in cyclic phosphorylation, so NADPH is not produced. Therefore, the only product of cyclic phosphorylation is ATP.

4130. Total NADH formed by one glucose molecule during Krebs cycle are:

• A. 6
• B. 3
• C. 8
• D. 18

Explanation: The total NADH formed by one glucose molecule during the Krebs cycle is 3*2=6. The Krebs cycle is a series of chemical reactions that occur in the mitochondria of cells. It is the second stage of cellular respiration, and it is responsible for the production of ATP. There are two cycles of krebs cycle per glucose molecule. During the Krebs cycle, six molecules of NADH are produced. These molecules are produced in the following reactions: