Bio-13: Photosynthesis in Higher Plants25 Questions
1. Who demonstrated that oxygen evolved during photosynthesis comes from water and not from carbon dioxide using purple and green sulfur bacteria?
A. C. van Niel
B. Joseph Priestley
C. Jan Ingenhousz
D. Julius von Sachs
Answer: A. C. van Niel
Explanation: Cornelius van Niel based on his studies of purple and green bacteria demonstrated that photosynthesis is a light-dependent reaction in which hydrogen from a suitable oxidizable compound reduces carbon dioxide to carbohydrates.
2. Who plotted the first action spectrum of photosynthesis using a green alga Cladophora and aerobic bacteria?
A. T.W. Engelmann
B. Joseph Priestley
C. Jan Ingenhousz
D. Melvin Calvin
Answer: A. T.W. Engelmann
Explanation: T.W. Engelmann split light into its spectral components using a prism and illuminated Cladophora placed in a suspension of aerobic bacteria to observe oxygen evolution in blue and red light regions.
3. In a chloroplast, the light reactions take place in the:
A. Thylakoid membranes / Grana
B. Stroma
C. Outer membrane
D. Periplastidial space
Answer: A. Thylakoid membranes / Grana
Explanation: The membrane system (grana and stroma lamellae) is responsible for trapping light energy and synthesizing ATP and NADPH (Light Reaction).
4. The primary photosynthetic pigment in higher plants that appears bright or blue-green on a chromatogram is:
A. Chlorophyll a
B. Chlorophyll b
C. Xanthophyll
D. Carotenoid
Answer: A. Chlorophyll a
Explanation: Chlorophyll a shows a bright or blue-green color in paper chromatography, Chlorophyll b is yellow-green, xanthophylls are yellow, and carotenoids are yellow to yellow-orange.
5. The reaction center of Photosystem I (PS I) has an absorption peak at:
A. 700 nm
B. 680 nm
C. 400 nm
D. 550 nm
Answer: A. 700 nm
Explanation: The reaction center chlorophyll a molecule in PS I has an absorption peak at 700 nm, hence called P700, whereas in PS II it absorbs at 680 nm (P680).
6. Water splitting complex (Photolysis of water) is physically associated with:
A. Photosystem II on the inner side of thylakoid membrane
B. Photosystem I on the outer side of thylakoid membrane
C. Stroma matrix
D. Cytochrome b6f complex in stroma lamellae
Answer: A. Photosystem II on the inner side of thylakoid membrane
Explanation: The water splitting complex is associated with PS II and is located on the inner side (lumen side) of the thylakoid membrane.
7. Cyclic photophosphorylation involves only:
A. Photosystem I
B. Photosystem II
C. Both PS I and PS II
D. Stroma enzymes
Answer: A. Photosystem I
Explanation: Cyclic photophosphorylation occurs when only PS I is functional, resulting in the synthesis of ATP only (no NADPH or $O_2$ is produced).
8. The enzyme ATP synthase consists of $F_0$ and $F_1$ parts. $F_0$ is located in the:
A. Embedded within the thylakoid membrane
B. Protruding on the stroma side
C. Lumen matrix
D. Outer membrane of chloroplast
Answer: A. Embedded within the thylakoid membrane
Explanation: $F_0$ is embedded in the thylakoid membrane and forms a transmembrane channel for proton diffusion, while $F_1$ protrudes on the stroma side.
9. According to Peter Mitchell's Chemiosmotic Hypothesis, ATP synthesis in chloroplasts requires a proton gradient created across the thylakoid membrane, where protons accumulate in the:
A. Thylakoid lumen
B. Stroma
C. Cytosol
D. Intermembrane space
Answer: A. Thylakoid lumen
Explanation: Protons accumulate inside the thylakoid lumen due to water splitting, electron movement through carriers, and NADP reductase activity on the stroma side.
10. The primary $CO_2$ acceptor in the C3 pathway (Calvin Cycle) is a 5-carbon ketose sugar called:
A. Ribulose-1,5-bisphosphate (RuBP)
B. Phosphoenolpyruvate (PEP)
C. Oxaloacetic acid (OAA)
D. Glyceraldehyde-3-phosphate
Answer: A. Ribulose-1,5-bisphosphate (RuBP)
Explanation: In C3 plants, the primary $CO_2$ acceptor is a 5-carbon sugar, RuBP, which combines with $CO_2$ catalyzed by RuBisCO.
11. The first stable product of $CO_2$ fixation in C3 plants is:
A. 3-Phosphoglyceric acid (PGA)
B. Oxaloacetic acid (OAA)
C. Malic acid
D. RuBP
Answer: A. 3-Phosphoglyceric acid (PGA)
Explanation: Melvin Calvin discovered that the first stable product formed after $CO_2$ fixation in C3 plants is a 3-carbon organic acid, 3-PGA.
12. How many ATP and NADPH molecules are required for the synthesis of one molecule of glucose through the Calvin cycle?
A. 18 ATP and 12 NADPH
B. 12 ATP and 12 NADPH
C. 30 ATP and 12 NADPH
D. 18 ATP and 18 NADPH
Answer: A. 18 ATP and 12 NADPH
Explanation: For every $CO_2$ molecule fixed, 3 ATP and 2 NADPH are required. For 6 turns (1 glucose molecule), $6 \times 3 = 18$ ATP and $6 \times 2 = 12$ NADPH are consumed.
13. C4 plants possess a characteristic leaf anatomy called:
A. Kranz anatomy
B. Isobilateral anatomy
C. Dorsiventral anatomy
D. Xeromorphic anatomy
Answer: A. Kranz anatomy
Explanation: C4 plants have large bundle sheath cells arranged in a wreath-like manner around vascular bundles, known as Kranz anatomy.
14. The primary $CO_2$ acceptor in C4 plants is:
A. Phosphoenolpyruvate (PEP)
B. RuBP
C. Oxaloacetic acid
D. Pyruvate
Answer: A. Phosphoenolpyruvate (PEP)
Explanation: In C4 plants, the primary $CO_2$ acceptor is a 3-carbon compound phosphoenolpyruvate (PEP) present in mesophyll cells.
15. In C4 plants, the enzyme PEP carboxylase (PEPcase) is located in:
A. Mesophyll cells
B. Bundle sheath cells
C. Epidermal cells
D. Xylem parenchyma
Answer: A. Mesophyll cells
Explanation: Mesophyll cells of C4 plants lack RuBisCO but possess PEPcase, which fixes $CO_2$ into a 4-carbon acid (OAA).
16. The Calvin cycle (C3 cycle) in C4 plants takes place in the:
A. Bundle sheath cells
B. Mesophyll cells
C. Guard cells
D. Epidermal cells
Answer: A. Bundle sheath cells
Explanation: Bundle sheath cells in C4 plants are rich in RuBisCO and lack PEPcase; hence, the Calvin cycle takes place in bundle sheath cells.
17. Photorespiration is a wasteful process because it produces neither ATP nor sugars, and it is initiated when RuBisCO binds to:
A. Oxygen ($O_2$)
B. Carbon dioxide ($CO_2$)
C. Water ($H_2O$)
D. Nitrogen ($N_2$)
Answer: A. Oxygen ($O_2$)
Explanation: RuBisCO has active sites for both $CO_2$ and $O_2$. When $O_2$ binds, RuBP is converted to 1 molecule of PGA and 1 molecule of phosphoglycolate, wasting energy.
18. Which group of plants does NOT undergo photorespiration?
A. C4 plants
B. C3 plants
C. Algae
D. Bryophytes
Answer: A. C4 plants
Explanation: C4 plants have a mechanism that increases $CO_2$ concentration at the RuBisCO enzyme site in bundle sheath cells, ensuring photorespiration does not occur.
19. Law of Limiting Factors was proposed by Blackman in the year:
A. 1905
B. 1860
C. 1931
D. 1954
Answer: A. 1905
Explanation: F.F. Blackman (1905) formulated the Law of Limiting Factors, stating that if a chemical process is affected by more than one factor, its rate is determined by the factor nearest to its minimal value.
20. Light saturation for photosynthesis occurs at what percentage of full sunlight?
A. 10%
B. 50%
C. 75%
D. 100%
Answer: A. 10%
Explanation: Except for plants in shade or dense forests, light is rarely a limiting factor in nature because light saturation occurs at 10% of full sunlight.
21. What is the atmospheric concentration of $CO_2$ at which C3 plants show saturation?
A. 450 $\mu L L^{-1}$
B. 360 $\mu L L^{-1}$
C. 200 $\mu L L^{-1}$
D. 600 $\mu L L^{-1}$
Answer: A. 450 $\mu L L^{-1}$
Explanation: C4 plants saturate at about 360 $\mu L L^{-1}$, whereas C3 plants respond to increased $CO_2$ concentration and saturation is seen only beyond 450 $\mu L L^{-1}$.
22. Which cell organelles are involved in the photorespiratory pathway (C2 cycle)?
A. Chloroplast, Peroxisome, and Mitochondria
B. Chloroplast, Golgi body, and Ribosome
C. Mitochondria, Endoplasmic reticulum, and Lysosome
D. Chloroplast, Nucleus, and Vacuole
Answer: A. Chloroplast, Peroxisome, and Mitochondria
Explanation: Photorespiration requires sequential cooperation among three organelles: chloroplast, peroxisome, and mitochondrion.
23. In CAM (Crassulacean Acid Metabolism) plants, stomata remain:
A. Open during night and closed during day
B. Open during day and closed during night
C. Continuously open
D. Continuously closed
Answer: A. Open during night and closed during day
Explanation: CAM plants (succulents like pineapple, cactus) keep stomata open at night (scotoactive) to absorb $CO_2$ and minimize water loss during dry hot days.
24. Total number of ATP consumed to produce one molecule of glucose in C4 plants is:
A. 30 ATP
B. 18 ATP
C. 12 ATP
D. 24 ATP
Answer: A. 30 ATP
Explanation: C4 plants require 5 ATP per $CO_2$ fixed (3 for Calvin cycle + 2 for PEP regeneration). For 6 $CO_2$, total ATP = $6 \times 5 = 30$ ATP.
25. Which mineral elements are directly involved in the oxygen-evolving complex during photosynthesis?
A. Manganese, Chlorine, and Calcium
B. Iron, Magnesium, and Zinc
C. Copper, Boron, and Molybdenum
D. Potassium, Sulfur, and Phosphorus
Answer: A. Manganese, Chlorine, and Calcium
Explanation: $Mn^{2+}$, $Cl^-$, and $Ca^{2+}$ ions are essential cofactors for the oxygen-evolving complex in Photosystem II during water photolysis.
