All Free Biology MCQs with Answers

3351. What are the different stages of the Calvin cycle?

• A. Carbon fixation
• B. RUBP regeneration
• C. Reduction
• D. Carbon fixation,Reduction, and RUBP regeneration

Explanation: The correct answer is Carbon fixation,Reduction,and RUBP regeneration. The Calvin cycle involves three crucial stages: Carbon fixation, where CO2 is attached to a 5-carbon sugar; Reduction, where ATP and NADPH are used to transform 3-phosphoglycerate into G3P; and RUBP regeneration, where the cycle's initial 5-carbon molecule is regenerated. Option A only mentions Carbon fixation, and Option C only mentions Reduction, making them incomplete. RUBP regeneration is essential for the cycle's continuity; thus, combining all these steps reflects the full cycle.

3352. Each Kreb's cycle forms how many molecules of NADH?

• A. 3
• B. 2
• C. 4
• D. 1

Explanation: 1 NADH molecule is produced at each of the following stages of a single Krebs cycle; therefore, 3 NADH molecules in total.1. Conversion of isocitrate to alpha-ketoglutarate2. Conversion of alpha-ketoglutarate to succinyl-CoA3. Conversion of malate to oxaloacetate

3353. Photosystems are located in:

• A. Stroma
• B. Chloroplast envelope
• C. Thylakoid membranes
• D. The intergrana

Explanation: The thylakoid membrane systems of cyanobacteria and of plant and algal chloroplasts contain the specialized photosystems, photosystem I (PSI), and photosystem II (PSII), in which the reaction centers photochemically transform light energy into usable chemical energy in the form of ATP and NADPH through photosynthetic electron transport (PET).

3354. What is produced in the muscle cells during extreme physical activity?

• A. Acetyl coA
• B. Alcohol
• C. Lactic acid
• D. All of these

Explanation: Muscle cells perform lactic acid fermentation (a form of anaerobic respiration) during vigorous exercise due to decrease amount or absence of oxygen.

3355. The synthesis of ATP in the presence of oxygen is called?

• A. Respiration
• B. Calvin cycle
• C. Oxidative phosphorylation
• D. Chemiosmosis

Explanation: Oxidative phosphorylation is the process by which ATP synthesis is coupled to the movement of electrons through the mitochondrial electron transport chain and the associated consumption of oxygen.

3356. Photosynthesis is a process in which _ compounds of carbon and hydrogen are reduced to carbohydrate-like compounds (glucose) using light energy.

• A. Organic
• B. Energy-poor
• C. Energy-rich
• D. Reduced

Explanation: During photosynthesis, energy-rich carbohydrates are formed from inorganic compounds like carbon dioxide and water that have much less chemical energy stored in them.

3357. What percentage of carbon dioxide does air contain?

• A. 0.02-0.03%
• B. 0.03-0.04%
• C. 0.04-0.05%
• D. 0.05-0.06%

Explanation: The Earth's atmosphere contains about 0.03-0.04 % carbon dioxide.Hence, B is the correct option.

3358. About what percentage of photosynthesis is carried by terrestrial plants, while the rest occurs in ocean, lakes, and ponds?

• A. 40
• B. 10
• C. 20
• D. 30

Explanation: 90% of total photosynthesis is carried out by aquatic plants. Most of them are marine algae, which account for nearly 80%. The rest is produced by freshwater algae about 10%. Only the remaining 10% of total photosynthesis is performed by land plants.Hence, B is the correct option.

3359. What is generated during non-cyclic flow of photosynthesis?

• A. ATP
• B. NADPH
• C. Oxygen
• D. All of these options are correct

Explanation: During the non-cyclic electron flow of photosynthesis, which occurs in the thylakoid membranes of the chloroplasts, light energy is used to produce ATP and NADPH. These molecules are essential energy carriers for the Calvin cycle, the next stage of photosynthesis. Additionally, oxygen is produced as a byproduct from the splitting of water molecules. Therefore, the correct answer is that all these substances-ATP, NADPH, and oxygen-are generated during this process.Options A, B, and C individually describe components that are indeed produced, but each misses the full picture, which is captured by Option D.

3360. Carbon dioxide is fixed in:

• A. Light reaction
• B. Dark reaction
• C. Aerobic respiration
• D. Anaerobic respiration

Explanation: The dark reaction, or light-independent reaction, occurs in the stroma of the chloroplast and involves the fixation of carbon dioxide through the Calvin cycle. This process does not directly require light and can occur in the absence of light.