Photosynthesis - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Case Study 1: Experiment to test the necessity of light for photosynthesis.

1. Why destarch?
   • Answer: To ensure that any starch found at the end of the experiment was synthesized during the experiment, not before.
2. boiling in alcohol?
   • Answer: To remove chlorophyll (decolorize the leaf) so that the blue-black color change with Iodine is clearly visible.
3. Designing: Predict observation.
   • Answer: Exposed part turns blue-black (starch present). Covered part stays brown/yellow (no starch).
4. Analysis: Why use a water bath?
   • Answer: Alcohol is highly inflammable and should not be heated directly over a flame.
5. If forgot to destarch?
   • Answer: The entire leaf would turn blue-black, giving a false-positive result for the covered part.

Case Study 2: Engelmann's experiment with Spirogyra and aerobic bacteria. 6. Conclusion on wavelengths.

• Answer: Blue and red light are the most effective for photosynthesis.

7. Why did bacteria accumulate?
   • Answer: Photosynthesis was highest in blue and red regions, releasing the most Oxygen. Aerobic bacteria move towards oxygen-rich areas (Chemotaxis).
8. Creating: Action Spectrum graph.
   • Answer: [Graph showing two peaks, one in blue and one in red region].
9. Critical Thinking: Why do leaves appear green?
   • Answer: Green light is reflected or transmitted by the leaf, not absorbed.
10. Role of Chlorophyll a and b.
    • Answer: Chlorophyll a is the primary pigment (Reaction center). Chlorophyll b is an accessory pigment that captures light and passes it to Chlorophyll a.

Section B: Assertion-Reasoning Questions

Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.

11. Assertion (A): Rate of photosynthesis decreases at very high temps. Reason (R): Enzymes are denatured.
    • Answer: (a) Both A and R are true and R is the correct explanation.
12. Assertion (A): Dark reaction occurs only at night. Reason (R): It is light-independent.
    • Answer: (d) A is false but R is true. (It occurs during the day using products of light reaction).
13. Assertion (A): Oxygen comes from water. Reason (R): Photolysis splits H2O.
    • Answer: (a) Both A and R are true and R is the correct explanation.
14. Assertion (A): Green plants are transducers. Reason (R): They convert solar energy to chemical energy.
    • Answer: (a) Both A and R are true and R is the correct explanation.
15. Assertion (A): Opening of stomata facilitates photosynthesis. Reason (R): It allows CO2 diffusion.
    • Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

16. Designing: Mohl's Half-Leaf Experiment.
    • Answer: Part of leaf inside bottle with KOH (absorbs CO2). After starch test, part inside bottle shows no starch.
17. Creating: Flowchart.
    • Answer: Light Phase (Grana, uses Light/H2O, produces ATP/NADPH/O2) -> Dark Phase (Stroma, uses CO2/ATP/NADPH, produces Glucose).
18. Analysis: Plant in atmosphere without CO2.
    • Answer: Photosynthesis stops. It will use stored starch for respiration until it's exhausted, then die.
19. Designing: Chloroplast diagram.
    • Answer: [Description: Outer/Inner membrane, stacks of Thylakoids (Grana), fluid Stroma]. Chlorophyll is in Thylakoid membranes.
20. Visualisation: Balanced equation.
    • Answer: 6CO2 + 12H2O --(Light / Chlorophyll)--> C6H12O6 + 6H2O + 6O2.
21. Application: Sleeping under a tree.
    • Answer: At night, trees only respire, releasing CO2 and taking in O2, which can cause discomfort/suffocation.
22. Creating: World with Green-light plants.
    • Answer: Plants would likely appear Red or Purple (reflecting what they don't use).
23. Analysis: Limiting Factors.
    • Answer: The rate is determined by the factor that is at its lowest level (e.g., low CO2 even in bright light).
24. Designing: Phosphorylation vs Photophosphorylation.
    • Answer: Photophosphorylation uses light energy to add phosphate to ADP.
25. Creating: Carbon Cycle role.
    • Answer: Photosynthesis is the only major process that removes CO2 from the atmosphere and fixes it into organic matter.

Section D: Competency & Critical Thinking

26. Photolysis fate.
    • Answer: H+ ions reduce NADP to NADPH. Electrons (e-) replace those lost by Chlorophyll. O is released as gas.
27. Scenario: Why not land plants for O2 bubbles?
    • Answer: In land plants, O2 diffuses out through stomata; in aquatic plants, it's released as visible bubbles through the water.
28. Critical Thinking: Oxidation-Reduction.
    • Answer: Water is oxidized (loses H+); CO2 is reduced (gains H+).
29. Application: Pollution effect.
    • Answer: Dust blocks sunlight and clogs stomata, reducing both light absorption and CO2 entry.
30. Palisade vs Spongy.
    • Answer: Palisade has more chloroplasts and is tightly packed for maximum light absorption. Spongy has air spaces for gas exchange.
31. Diagram Based: Saturation point.
    • Answer: The point where the curve flattens out.
32. Fate of Glucose.
    • Answer: Used for energy, converted to Starch for storage, or Sucrose for transport.
33. Analysis: Variegated leaves.
    • Answer: Shows that chlorophyll is essential for photosynthesis.
34. Competency: ATP and NADPH role.
    • Answer: They provide the energy and reducing power needed to convert CO2 into Glucose in the Calvin Cycle.
35. Case: Greenhouse yield.
    • Answer: Increase light (LEDs) and supplement CO2 levels (CO2 generators).
36. Creating: Intermittent light.
    • Answer: Yes, because the light reaction is fast, but the dark reaction can continue in the intervals between light pulses.
37. Designing: ADP to ATP.
    • Answer: Like a rechargeable battery getting charged.
38. Application: Global Warming.
    • Answer: Higher CO2 may increase photosynthesis, but the associated heat and drought might offset this benefit.
39. Critical Thinking: Artificial light.
    • Answer: Yes, as long as the light contains the required wavelengths (Blue and Red).
40. Analysis: Leaf adaptations.
    • Answer: Large surface area, thin (short diffusion path), extensive vein network (transport).

Section E: Advanced Competency

41. Scenario: First stable product.
    • Answer: Phosphoglyceric Acid (PGA). It has 3 Carbon atoms.
42. Designing: Z-scheme concept.
    • Answer: Light excites electrons -> move through ETC -> produce ATP/NADPH.
43. Application: Sugarcane vs Wheat.
    • Answer: Sugarcane (C4) can continue photosynthesis at very low CO2 and high temps by avoiding photorespiration.
44. Creating: Respiration vs Photosynthesis.
    • Answer: [Respiration: All cells, 24h, mitochondria, catabolic. Photosynthesis: Green cells, day, chloroplast, anabolic].
45. Case Study: Green light death.
    • Answer: Plants cannot absorb green light; no energy for light reaction.
46. Accessory Pigments.
    • Answer: They absorb wavelengths not captured by Chlorophyll a and protect it from photo-oxidation.
47. Critical Thinking: CAM plants.
    • Answer: They open stomata at night to store CO2 as organic acids, then use it during the day when stomata are closed.
48. Analysis: Water stress.
    • Answer: Lack of water causes stomata to close to save water, which limits CO2 supply.
49. Designing: Temp graph.
    • Answer: Bell curve; peak at 25-35°C.
50. Creating: Solar leaf.
    • Answer: Flexible, self-healing, water-splitting technology.