All Free Biology MCQs with Answers

3321. Which is the correct order of energy transfer from accessory pigments to main photo synthetic pigment?

• A. Carotenoids, Chlorophyll a, Chlorophyll b
• B. Chlorophyll b, Carotenoids, Chlorophyll a
• C. Carotenoids, chlorophyll b, Chlorophyll a
• D. Chlorophyll a, Chlorophyll b, Carotenoids

Explanation: In the process of photosynthesis, energy transfer occurs in a specific sequence: from accessory pigments to the main photosynthetic pigment. Carotenoids capture light energy and pass it to chlorophyll b. Chlorophyll b then transfers this energy to chlorophyll a, where it is used in the photosynthetic reactions. Options A, B, and D are incorrect because they do not follow this correct sequence.

3322. What does NADPH2 provide during photosynthesis?

• A. Energized electrons
• B. Uncharged electrons
• C. Energy
• D. All of these

Explanation: NADPH, produced during the light-dependent reactions of photosynthesis, provides high-energy electrons and hydrogen ions to the Calvin cycle. These electrons are crucial for the reduction of carbon compounds, leading to the synthesis of glucose. Options B and C are incorrect because the Calvin cycle requires specifically energized electrons, not uncharged ones or standalone energy. Option D is incorrect as NADPH does not provide all of these; it specifically provides energized electrons.

3323. The difference in photosynthesis spectrum and action spectrum occurs due to _.

• A. Carbon dioxide
• B. Oxygen
• C. Carotenoids
• D. Wavelength

Explanation: Photosynthesis is a complex process that converts light energy into chemical energy, producing glucose and oxygen. The difference between the photosynthesis spectrum and the action spectrum is due to the presence of carotenoids, which extend the range of light wavelengths that plants can utilize for photosynthesis. Additionally, carbon dioxide is a necessary raw material, and oxygen is a byproduct of this vital biological process. The wavelength of light affects the efficiency of photosynthesis, and only certain wavelengths are effectively used by the plant's pigments to drive the process.

3324. The oxidation phase of glycolysis is _.

• A. Energy consuming
• B. Energy yielding
• C. Net neutralization of energy
• D. Both a and c

Explanation: The oxidation phase of glycolysis is energy-yielding because it results in the production of energy-rich molecules (NADH and ATP) that can be used by the cell to fuel other metabolic processes.

3325. Which of the following statements about the head of a chlorophyll molecule is incorrect?

• A. It is a porphyrin ring or tetrapyrrole ring structure
• B. It is flat, square and light absorbing
• C. Composed of carbon and nitrogen atoms with magnesium as the central metal ion
• D. It is hydrophobic

Explanation: Chlorophyll molecules have a complex structure consisting of the hydrophobic tail region and hydrophilic head region because they need to interact with the surrounding aqueous environment. Now this is the wrong option and the question did ask for an incorrect one, hence option D is right.

3326. Phosphofructokinases enzyme converts fructose-6-phosphate into:

• A. Fructose-1,4-phosphate
• B. Fructose-1,6-bisphosphate
• C. Bisphosphate
• D. Fructose

Explanation: Phosphofructokinase (PFK) plays a critical role in glycolysis by catalyzing the conversion of fructose-6-phosphate into fructose-1,6-bisphosphate. This reaction involves the transfer of a phosphate group from ATP to fructose-6-phosphate, forming fructose-1,6-bisphosphate and ADP. This step is key for regulating the glycolytic pathway. Option B is correct because it reflects the specific phosphorylated product of this reaction. Option A is incorrect because it specifies the wrong positions for phosphorylation. Option C is too vague, as it does not specify the positions of the phosphate groups. Option D is incorrect because it suggests a conversion that does not occur in this enzymatic reaction.

3327. At what times is there a no net gaseous exchange between leaves and the atmosphere?

• A. Day
• B. Night
• C. Dawn and Dusk
• D. Midnight

Explanation: Dusk there is no net gaseous exchange between leaves and atmosphere. At dawn and dusk,when light intensity is low, the rate of photosynthesis and respiration may, for a short time, equal one another. Thus the oxygen released from photosynthesis is just the amount required for cellular respiration. Also, the carbon dioxide released by respiration just equals the quantity required by photosynthesizing cells. At this moment there is no net gas exchange between the leaves and the atmosphere. This is termed as compensation point.

3328. What is reduced during sugar production in photosynthesis?

• A. NADH
• B. DNA
• C. Oxygen
• D. Carbon dioxide

Explanation: Option D is correct because, in the Calvin cycle of photosynthesis, carbon dioxide is reduced to produce carbohydrates (sugars). This reduction is crucial for forming glucose and other sugars. The other options are incorrect as NADH is primarily involved in cellular respiration, DNA is not directly involved in this part of photosynthesis, and oxygen is a product of the light-dependent reactions, not involved in the reduction process of sugar production.

3329. When 100% carbon is oxidized to CO2, the efficiency of such respiration is?

• A. 40%
• B. 60%
• C. 90%
• D. 100%

Explanation: Option A suggests that the efficiency of respiration, when 100% carbon is oxidized to CO2, is 40%. It means that approximately 40% of the energy released during respiration is converted to ATP, while the remaining 60% is lost as heat.

3330. Cellular respiration is carried out in:

• A. Ribosome
• B. Mitochondria
• C. Chloroplast
• D. Golgi bodies

Explanation: Mitochondria are often referred to as the "powerhouses" of the cell because they are the primary sites of cellular respiration. These organelles have a double membrane and contain enzymes and other molecules necessary for the various steps of cellular respiration, such as glycolysis, the Krebs cycle (also known as the citric acid cycle), and the electron transport chain.