All Free Biology MCQs with Answers

3241. ATP synthase is located in the _ of the mitochondrion.

• A. Intermembrane space
• B. Outer membrane
• C. Matrix
• D. Inner membrane

Explanation: ATP synthase is located in the inner mitochondrial membrane of the mitochondrion. More specifically, it is embedded in the inner mitochondrial membrane and protrudes into the mitochondrial matrix. This location is crucial for the function of ATP synthase in the process of oxidative phosphorylation.

3242. FADH2 is produced in_:

• A. Glycolysis
• B. The oxidation of pyruvates
• C. Kreb's cycle
• D. All of these

Explanation: FADH2 (flavin adenine dinucleotide) is produced during cellular respiration, specifically in the citric acid cycle (also known as the Krebs cycle). The citric acid cycle is a series of chemical reactions that take place in the mitochondrial matrix, and it plays a central role in the breakdown of acetyl-CoA (a two-carbon compound derived from the breakdown of glucose) and the production of energy-rich molecules.

3243. NADPH2 is formed in photosynthesis but in respiration, it forms during _.

• A. HMP
• B. ETS
• C. Kreb's cycle
• D. None of these

Explanation: NADPH (reduced nicotinamide adenine dinucleotide phosphate) is more directly associated with other pathways, such as the pentose phosphate pathway (also known as the hexose monophosphate shunt or HMP). In the pentose phosphate pathway, glucose-6-phosphate is converted into ribulose-5-phosphate, and NADPH is produced during this process. The pathway serves various functions, including the generation of NADPH for biosynthetic processes and the reduction of oxidative stress.

3244. Succinate is oxidized and forms:

• A. FAD
• B. FADH
• C. FADH2
• D. NADH2

Explanation: Succinate is oxidized to fumarate in the citric acid cycle, and during this process, FAD is reduced to form FADH2. FADH2, along with NADH, plays a crucial role in the electron transport chain to produce ATP during oxidative phosphorylation. The overall reaction is: Succinate+FAD→Fumarate+FADH2

3245. The spent energy in the form of ADP is regenerated by mitochondria into which of the following?

• A. AMP
• B. ATP
• C. ADP
• D. All of these

Explanation: The correct answer is ATP. Mitochondria are known as the powerhouse of the cell because they convert ADP into ATP through cellular respiration, a process that includes glycolysis, the citric acid cycle, and the electron transport chain. ATP serves as the main energy carrier in the cell. Other options like AMP and ADP are not the end products of this energy regeneration process.

3246. In this stage of photosynthesis, ATP and NADPH converted to ADP+Pi and NADP+:

• A. Light dependent reaction
• B. Light independent reaction
• C. Both of these
• D. None of above

Explanation: The stage of photosynthesis where ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) are converted to ADP (adenosine diphosphate) + Pi (inorganic phosphate) and NADP+ is the Calvin Cycle, also known as the light-independent reactions or dark reactions.

3247. Oxygen plays _ role in respiration.

• A. It combines with acetyl-CoA at the start of the Krebs cycle
• B. It plays no role
• C. It is given off as a by-product during the oxidation of pyruvates
• D. It is the final electron acceptor at the end of the electron transport chain

Explanation: During oxidative phosphorylation, oxygen serves as the final electron acceptor in the electron transport chain. Electrons derived from the breakdown of glucose are passed through a series of protein complexes in the inner mitochondrial membrane, and oxygen ultimately accepts these electrons, forming water. This process is essential for the efficient production of ATP, the energy currency of the cell, from water molecules. The energy released by electrons is used for the generation of ATP by oxidative phosphorylation.

3248. Fermentation products produced by yeast include:

• A. H2O + CO2
• B. Methyl alcohol + CO2
• C. Methyl alcohol + water
• D. Ethyl alcohol + CO2

Explanation: Fermentation in yeast, particularly alcoholic fermentation, produces ethanol (alcohol) and carbon dioxide as the main products. Yeast cells produce ethanol (ethyl alcohol), which is commonly used in the production of alcoholic beverages and has industrial applications. Carbon dioxide is released as a byproduct of the fermentation process. In the context of baking, the carbon dioxide produced contributes to the leavening of bread, causing it to rise. The overall reaction for alcoholic fermentation in yeast is as follows: Glucose→2 Ethanol+2 Carbon Dioxide+Energy

3249. Dark reaction and light reaction of photosynthesis takes place in the:

• A. Stroma and grana of the chloroplast, respectively
• B. Grana and stroma of the chloroplast respectively
• C. Grana only
• D. Stroma only

Explanation: The light reactions occur in the thylakoid membra,nes, while the dark reactions (Calvin Cycle) ,take place in the stroma of the chloroplasts. Together, these processes enable the conversion of light energy into chemical energy stored in the form of carbohydrates.

3250. Glycolysis takes place in the _ of cells.

• A. Nucleus
• B. Mitochondria
• C. Golgi complex
• D. Cytoplasm

Explanation: Glycolysis, the first step of aerobic respiration, which results in the formation of two molecules of pyruvate from one molecule of glucose, occurs in the cytoplasm of the cell.