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Master Biology for NEET & Medical Entrance Exams

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NEET 45-Question Mock 45:00

Q1. The primary function of the "Light-harvesting complex" (LHC) is:

Explanation:
Option B is correct. The LHC consists of hundreds of pigment molecules that funnel energy to a single chlorophyll "a" molecule.

Q2. Which wavelength of light is least effective in photosynthesis?

Explanation:
Option C is correct. Chlorophyll reflects green light, which is why plants appear green; therefore, it is the least absorbed/effective.

Q3. The splitting of water is associated with:

Explanation:
Option B is correct. The Oxygen Evolving Complex (OEC) is physically located on the inner side of the thylakoid membrane associated with PS-II.

Q4. Non-cyclic photophosphorylation involves:

Explanation:
Option C is correct. Both systems work in series (the Z-scheme) to produce ATP and NADPH + H.

Q5. The final electron acceptor in non-cyclic electron transport is:

Explanation:
Option B is correct. In non-cyclic electron transport (light reactions of photosynthesis), electrons ultimately reduce NADP + to form NADPH.

Q6. In PS-II, the reaction center chlorophyll "a" has an absorption peak at:

Explanation:
Option B is correct. PS-II is called P680 because its reaction center chlorophyll absorbs light most efficiently at a wavelength of 680 nm.

Q7. Cyclic photophosphorylation results in the formation of:

Explanation:
Option C is correct. In cyclic photophosphorylation, electrons excited from Photosystem I (P700) return back to the same system. Since the electrons cycle back, no water is split and no NADP is reduced. Therefore, only ATP is produced.

Q8. According to Mitchell’s chemiosmotic hypothesis, ATP is synthesized when:

Explanation:
Option B is correct. According to the chemiosmotic hypothesis, a proton gradient is created across the thylakoid membrane during photosynthesis. Protons accumulate in the lumen and then flow back into the stroma through ATP synthase. This movement of protons provides the energy required to synthesize ATP.

Q9. The enzyme responsible for the reduction of NADP plus is located on:

Explanation:
Option B is correct. The enzyme NADP reductase is located on the stroma side of the thylakoid membrane. It reduces NADP plus to NADPH, which is then used in the dark reactions (Calvin cycle) that occur in the stroma.

Q10. Which of the following ions are required for the photolysis of water?

Explanation:
Option B is correct. Photolysis of water takes place in Photosystem II with the help of the oxygen-evolving complex. This complex requires manganese ions and chloride ions as essential cofactors for splitting water into oxygen, protons, and electrons.

Q11. The first stable product of the C₃ cycle is:

Explanation:
Option B is correct. In the C₃ cycle (Calvin cycle), carbon dioxide combines with RuBP to form an unstable 6-carbon compound, which immediately breaks down into two molecules of 3-phosphoglyceric acid (3-PGA). This is the first stable product of the cycle.

Q12. The most abundant enzyme in the world is:

Explanation:
Option B is correct. RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is the most abundant enzyme on Earth. It is present in very large amounts in green plants because it plays a key role in carbon fixation during the Calvin cycle of photosynthesis.

Q13. To produce one molecule of Glucose, the Calvin cycle must run:

Explanation:
Option C is correct. In each turn of the Calvin cycle, one molecule of carbon dioxide is fixed. Since glucose has six carbon atoms, the cycle must run six times to fix six molecules of carbon dioxide and ultimately form one molecule of glucose.

Q14. For the synthesis of one glucose molecule, the C₃ pathway requires:

Explanation:
Option A is correct. In the C₃ pathway (Calvin cycle), each turn fixes one molecule of carbon dioxide and uses 3 ATP and 2 NADPH. Since one glucose molecule requires 6 turns of the cycle, the total requirement becomes 18 ATP (3 × 6) and 12 NADPH (2 × 6).

Q15. RuBisCO has a high affinity for CO₂ when:

Explanation:
Option B is correct. RuBisCO can act as both a carboxylase (adds CO₂) and an oxygenase (adds O₂). When CO₂ concentration is high, RuBisCO preferentially binds CO₂ and catalyzes carbon fixation in the Calvin cycle.

Q16. “Kranz Anatomy” is a characteristic feature of:

Explanation:
Option B is correct. Kranz anatomy is found in C₄ plants. In this arrangement, bundle sheath cells form a wreath-like structure around the vascular bundles, and mesophyll cells surround the bundle sheath cells. This specialized structure helps in efficient carbon fixation by minimizing photorespiration.

Q17. The primary CO₂ acceptor in C₄ plants is:

Explanation:
Option B is correct. In C₄ plants, carbon dioxide is first fixed in the mesophyll cells by the enzyme PEP carboxylase. The primary CO₂ acceptor is phosphoenolpyruvate (PEP), which combines with CO₂ to form a 4-carbon compound (oxaloacetic acid).

Q18. In C₄ plants, the Calvin cycle (dark reaction) occurs in:

Explanation:
Option B is correct. In C₄ plants, the Calvin cycle takes place in the bundle sheath cells. CO₂ is first fixed in mesophyll cells and then transported to bundle sheath cells, where it is released at a high concentration for use in the Calvin cycle by RuBisCO. This arrangement reduces photorespiration.

Q19. Photorespiration is a wasteful process because:

Explanation:
Option A is correct. Photorespiration uses oxygen instead of carbon dioxide in RuBisCO activity, leading to the loss of previously fixed carbon as carbon dioxide. It also consumes energy (ATP and reducing power) without producing sugars, making it an energy-wasting process for the plant.

Q20. CAM plants keep their stomata closed during the day to:

Explanation:
Option B is correct. (Succulents), CAM (Crassulacean Acid Metabolism) plants live in dry conditions. They keep their stomata closed during the day to reduce water loss through transpiration. At night, when conditions are cooler and more humid, they open stomata and fix carbon dioxide for use during the day.

Q21. "Law of Limiting Factors" was proposed by:

Explanation:
Option D is correct. Blackman’s Law states that the rate is limited by the factor at its sub-optimal level.

Q22. At higher light intensities, the rate of photosynthesis:

Explanation:
Option C is correct. At low light intensity, the rate of photosynthesis increases with increasing light. However, at higher light intensities, it reaches a point of saturation where light is no longer the limiting factor. At this stage, other factors such as carbon dioxide concentration and temperature limit the rate, so it becomes constant.

Q23. Which of the following is NOT a limiting factor under normal field conditions for C₃ plants?

Explanation:
Option D is correct. Under normal field conditions, the rate of photosynthesis in C₃ plants is usually limited by environmental factors such as carbon dioxide concentration, light intensity, and water availability. Chlorophyll content is generally not a limiting factor under normal conditions because leaves typically have sufficient chlorophyll for photosynthesis.

Q24. What is the CO₂ saturation point for C₄ plants?

Explanation:
Option B is correct. C₄ plants have a CO₂-concentrating mechanism, so they reach saturation at relatively low CO₂ concentrations compared to C₃ plants. Their photosynthetic rate typically becomes saturated around ambient or slightly above ambient CO₂ levels (about 350–360 µL/L).

Q25. Temperature mainly affects:

Explanation:
Option C is correct. Enzymatic dark reactions, Temperature mainly affects the dark reactions (Calvin cycle) because they are enzyme-controlled processes. Enzymes such as RuBisCO function optimally within a specific temperature range, and their activity decreases at very low or very high temperatures.

Q26. Who used *Cladophora* and a prism to show the action spectrum?

Explanation:
Option B is correct. Theodor W. Engelmann — He used a prism to split light and observed that aerobic bacteria accumulated in the red and blue regions, indicating the wavelengths most effective for photosynthesis.

Q27. Van Niel’s experiment on purple and green bacteria demonstrated that:

Explanation:
Option B is correct. Cornelis van Niel studied photosynthetic bacteria such as purple and green sulfur bacteria. He used hydrogen sulfide (H 2 ​ S) instead of water in photosynthesis and observed that sulfur was released instead of oxygen. From this, he concluded that in green plants, the oxygen released during photosynthesis comes from water (H 2 ​ O), not from carbon dioxide (CO 2 ​ ).

Q28. The first action spectrum of photosynthesis was described by:

Explanation:
Option A is correct. Theodor W. Engelmann demonstrated the first action spectrum of photosynthesis using a filamentous alga and aerobic bacteria. The bacteria clustered in regions where oxygen was released the most, indicating the wavelengths of light most effective for photosynthesis.

Q29. Which pigment acts as the reaction center in Photosystem I (PS I)?

Explanation:
Option C is correct. The reaction center of Photosystem I (PS I) is a special form of chlorophyll a known as P₇₀₀, which absorbs light most efficiently at a wavelength of 700 nm.

Q30. Carotenoids and chlorophyll b are called “accessory pigments” because:

Explanation:
Option B is correct. Accessory pigments such as carotenoids and chlorophyll b absorb light at wavelengths that chlorophyll a cannot, thereby broadening the spectrum of light used in photosynthesis. They also help protect chlorophyll a from photo-oxidative damage by dissipating excess energy.

Q31. In C4 plants, the four-carbon compound formed in mesophyll cells is:

Explanation:
Option A is correct. In C4 plants, carbon dioxide is initially fixed in mesophyll cells to form oxaloacetic acid (OAA), a four-carbon compound. OAA is then usually converted into malic acid or aspartic acid, which are transported to bundle sheath cells for further processing in the Calvin cycle.

Q32. The enzyme PEP carboxylase (PEPcase) is found in:

Explanation:
Option B is correct. PEP carboxylase (PEPcase) is present in the mesophyll cells of C₄ plants, where it catalyzes the initial fixation of CO₂ into a 4-carbon compound (oxaloacetate). It is absent in C₃ plants and is not found in bundle sheath cells in C₄ pathway plants.

Q33. Photosynthesis is a:

Explanation:
Option B is correct. Photosynthesis is an anabolic process because it synthesizes glucose from carbon dioxide and water. It is also endergonic, as it requires energy input in the form of light to drive the reactions.

Q34. Radioactive 14C was used by Melvin Calvin to discover:

Explanation:
Option B is correct. Melvin Calvin used radioactive carbon 14C in algal photosynthesis experiments to trace the pathway of carbon during the dark reactions. This led to the discovery of the Calvin cycle, which explains carbon fixation in photosynthesis.

Q35. Oxygenic photosynthesis occurs in:

Explanation:
Option D is correct. Cyanobacteria were the first to perform oxygen-evolving photosynthesis.

Q36. Cyclic photophosphorylation is the source of ATP in:

Explanation:
Option A is correct. Stroma lamellae lack Photosystem II (PS II) and the NADP⁺ reductase enzyme. Therefore, only cyclic photophosphorylation occurs here, which produces ATP but not NADPH or oxygen.

Q37. How many molecules of NADPH are required to fix one CO2 molecule in the C₃ cycle?

Explanation:
Option A is correct. In the C₃ (Calvin) cycle, the fixation of one CO2 molecule requires 2 NADPH and 3 ATP molecules.

Q38. The process that makes an important difference between C3 and C4 plants is:

Explanation:
Option C is correct. Photorespiration occurs significantly in C3 plants, reducing photosynthetic efficiency. In C4 plants, this process is largely minimized due to a CO₂-concentrating mechanism, which helps suppress photorespiration. C4 plants have evolved to bypass photorespiration entirely.

Q39. During the light reaction, the pH of the thylakoid lumen:

Explanation:
Option C is correct. During the light reaction, protons (H⁺) accumulate in the thylakoid lumen due to photolysis of water and proton pumping through the electron transport chain. This increases acidity, thereby lowering the pH.

Q40. The primary CO2 acceptor in C3 plants is:

Explanation:
Option B is correct. In the C3 (Calvin) cycle, CO2 is fixed by carboxylation of ribulose-1,5-bisphosphate (RuBP), a 5-carbon compound, catalyzed by the enzyme RuBisCO. This reaction forms an unstable 6-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA).

Q41. Water stress causes stomata to close, which:

Explanation:
Option A is correct. Under water stress, stomata close to minimize water loss through transpiration. This closure restricts the diffusion of CO2 into the leaf, thereby reducing its availability for photosynthesis.

Q42. Which of the following is a C4 plant?

Explanation:
Option C is correct. Maize is a C4 plant that utilizes the Hatch–Slack pathway for carbon fixation. Other common C4 plants include sorghum and sugarcane, whereas wheat, rice, and tomato are C3 plants.

Q43. The sugar exported from leaves to other parts of the plant is usually:

Explanation:
Option C is correct. Sucrose is the principal transport form of carbohydrate in plants, translocated through the phloem from source (leaves) to sink tissues. In contrast, starch serves as the primary storage form of carbohydrate.

Q44. Where does the “photo” (light-dependent) part of photosynthesis occur?

Explanation:
Option B is correct. The light-dependent reactions of photosynthesis occur in the thylakoid membranes of chloroplasts, where light energy is absorbed and converted into chemical energy in the form of ATP and NADPH.

Q45. During photosynthesis, the energy captured from sunlight is ultimately transformed and stored in which of the following forms?

Explanation:
Option C is correct. Photosynthesis converts light energy into chemical energy stored in the bonds of organic molecules (such as glucose), primarily through the formation of ATP and NADPH during the light reactions and carbohydrates during the Calvin cycle.

Test Summary