Photosynthesis - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

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

Why destarch?
- Answer: To ensure that any starch found at the end of the experiment was synthesized during the experiment, not before.
boiling in alcohol?
- Answer: To remove chlorophyll (decolorize the leaf) so that the blue-black color change with Iodine is clearly visible.
Designing: Predict observation.
- Answer: Exposed part turns blue-black (starch present). Covered part stays brown/yellow (no starch).
Analysis: Why use a water bath?
- Answer: Alcohol is highly inflammable and should not be heated directly over a flame.
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.

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).
Creating: Action Spectrum graph.
- Answer: [Graph showing two peaks, one in blue and one in red region].
Critical Thinking: Why do leaves appear green?
- Answer: Green light is reflected or transmitted by the leaf, not absorbed.
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.

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.
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).
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.
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.
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)

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.
Creating: Flowchart.
- Answer: Light Phase (Grana, uses Light/H2O, produces ATP/NADPH/O2) -> Dark Phase (Stroma, uses CO2/ATP/NADPH, produces Glucose).
Analysis: Plant in atmosphere without CO2.
- Answer: Photosynthesis stops. It will use stored starch for respiration until it's exhausted, then die.
Designing: Chloroplast diagram.
- Answer: [Description: Outer/Inner membrane, stacks of Thylakoids (Grana), fluid Stroma]. Chlorophyll is in Thylakoid membranes.
Visualisation: Balanced equation.
- Answer: 6CO2 + 12H2O --(Light / Chlorophyll)--> C6H12O6 + 6H2O + 6O2.
Application: Sleeping under a tree.
- Answer: At night, trees only respire, releasing CO2 and taking in O2, which can cause discomfort/suffocation.
Creating: World with Green-light plants.
- Answer: Plants would likely appear Red or Purple (reflecting what they don't use).
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).
Designing: Phosphorylation vs Photophosphorylation.
- Answer: Photophosphorylation uses light energy to add phosphate to ADP.
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

Photolysis fate.
- Answer: H+ ions reduce NADP to NADPH. Electrons (e-) replace those lost by Chlorophyll. O is released as gas.
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.
Critical Thinking: Oxidation-Reduction.
- Answer: Water is oxidized (loses H+); CO2 is reduced (gains H+).
Application: Pollution effect.
- Answer: Dust blocks sunlight and clogs stomata, reducing both light absorption and CO2 entry.
Palisade vs Spongy.
- Answer: Palisade has more chloroplasts and is tightly packed for maximum light absorption. Spongy has air spaces for gas exchange.
Diagram Based: Saturation point.
- Answer: The point where the curve flattens out.
Fate of Glucose.
- Answer: Used for energy, converted to Starch for storage, or Sucrose for transport.
Analysis: Variegated leaves.
- Answer: Shows that chlorophyll is essential for photosynthesis.
Competency: ATP and NADPH role.
- Answer: They provide the energy and reducing power needed to convert CO2 into Glucose in the Calvin Cycle.
Case: Greenhouse yield.
- Answer: Increase light (LEDs) and supplement CO2 levels (CO2 generators).
Creating: Intermittent light.
- Answer: Yes, because the light reaction is fast, but the dark reaction can continue in the intervals between light pulses.
Designing: ADP to ATP.
- Answer: Like a rechargeable battery getting charged.
Application: Global Warming.
- Answer: Higher CO2 may increase photosynthesis, but the associated heat and drought might offset this benefit.
Critical Thinking: Artificial light.
- Answer: Yes, as long as the light contains the required wavelengths (Blue and Red).
Analysis: Leaf adaptations.
- Answer: Large surface area, thin (short diffusion path), extensive vein network (transport).

Section E: Advanced Competency

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

Section A: Case-Based Questions

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

Why destarch?

Answer: To ensure that any starch found at the end of the experiment was synthesized during the experiment, not before.

boiling in alcohol?

Answer: To remove chlorophyll (decolorize the leaf) so that the blue-black color change with Iodine is clearly visible.

Designing: Predict observation.

Answer: Exposed part turns blue-black (starch present). Covered part stays brown/yellow (no starch).

Analysis: Why use a water bath?

Answer: Alcohol is highly inflammable and should not be heated directly over a flame.

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.

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).

Creating: Action Spectrum graph.

Answer: [Graph showing two peaks, one in blue and one in red region].

Critical Thinking: Why do leaves appear green?

Answer: Green light is reflected or transmitted by the leaf, not absorbed.

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.

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.

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).

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.

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.

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)

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.

Creating: Flowchart.

Answer: Light Phase (Grana, uses Light/H2O, produces ATP/NADPH/O2) -> Dark Phase (Stroma, uses CO2/ATP/NADPH, produces Glucose).

Analysis: Plant in atmosphere without CO2.

Answer: Photosynthesis stops. It will use stored starch for respiration until it's exhausted, then die.

Designing: Chloroplast diagram.

Answer: [Description: Outer/Inner membrane, stacks of Thylakoids (Grana), fluid Stroma]. Chlorophyll is in Thylakoid membranes.

Visualisation: Balanced equation.

Answer: 6CO2 + 12H2O --(Light / Chlorophyll)--> C6H12O6 + 6H2O + 6O2.

Application: Sleeping under a tree.

Answer: At night, trees only respire, releasing CO2 and taking in O2, which can cause discomfort/suffocation.

Creating: World with Green-light plants.

Answer: Plants would likely appear Red or Purple (reflecting what they don't use).

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).

Designing: Phosphorylation vs Photophosphorylation.

Answer: Photophosphorylation uses light energy to add phosphate to ADP.

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

Photolysis fate.

Answer: H+ ions reduce NADP to NADPH. Electrons (e-) replace those lost by Chlorophyll. O is released as gas.

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.

Critical Thinking: Oxidation-Reduction.

Answer: Water is oxidized (loses H+); CO2 is reduced (gains H+).

Application: Pollution effect.

Answer: Dust blocks sunlight and clogs stomata, reducing both light absorption and CO2 entry.

Palisade vs Spongy.

Answer: Palisade has more chloroplasts and is tightly packed for maximum light absorption. Spongy has air spaces for gas exchange.

Diagram Based: Saturation point.

Answer: The point where the curve flattens out.

Fate of Glucose.

Answer: Used for energy, converted to Starch for storage, or Sucrose for transport.

Analysis: Variegated leaves.

Answer: Shows that chlorophyll is essential for photosynthesis.

Competency: ATP and NADPH role.

Answer: They provide the energy and reducing power needed to convert CO2 into Glucose in the Calvin Cycle.

Case: Greenhouse yield.

Answer: Increase light (LEDs) and supplement CO2 levels (CO2 generators).

Creating: Intermittent light.

Answer: Yes, because the light reaction is fast, but the dark reaction can continue in the intervals between light pulses.

Designing: ADP to ATP.

Answer: Like a rechargeable battery getting charged.

Application: Global Warming.

Answer: Higher CO2 may increase photosynthesis, but the associated heat and drought might offset this benefit.

Critical Thinking: Artificial light.

Answer: Yes, as long as the light contains the required wavelengths (Blue and Red).

Analysis: Leaf adaptations.

Answer: Large surface area, thin (short diffusion path), extensive vein network (transport).

Section E: Advanced Competency

Scenario: First stable product.

Answer: Phosphoglyceric Acid (PGA). It has 3 Carbon atoms.

Designing: Z-scheme concept.

Answer: Light excites electrons -> move through ETC -> produce ATP/NADPH.

Application: Sugarcane vs Wheat.

Answer: Sugarcane (C4) can continue photosynthesis at very low CO2 and high temps by avoiding photorespiration.

Creating: Respiration vs Photosynthesis.

Answer: [Respiration: All cells, 24h, mitochondria, catabolic. Photosynthesis: Green cells, day, chloroplast, anabolic].

Case Study: Green light death.

Answer: Plants cannot absorb green light; no energy for light reaction.

Accessory Pigments.

Answer: They absorb wavelengths not captured by Chlorophyll a and protect it from photo-oxidation.

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.

Analysis: Water stress.

Answer: Lack of water causes stomata to close to save water, which limits CO2 supply.

Designing: Temp graph.

Answer: Bell curve; peak at 25-35°C.

Creating: Solar leaf.

Answer: Flexible, self-healing, water-splitting technology.

Photosynthesis

Photosynthesis - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Section B: Assertion-Reasoning Questions

Section C: Creating and Designing (Application & Analysis)

Section D: Competency & Critical Thinking

Section E: Advanced Competency

On this page

Photosynthesis

Photosynthesis - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Section B: Assertion-Reasoning Questions

Section C: Creating and Designing (Application & Analysis)

Section D: Competency & Critical Thinking

Section E: Advanced Competency

On this page