10.
A hydrilla plant is growing in a beaker with water. What will happen to the rate of
photosynthesis if you add sodium bicarbonate to the water?
a. It will remain unchanged
b. It will decrease
c. It will stop
d. It will increase
Hydrilla Photosynthesis Experiment
Correct Answer: d. It will increase
Adding sodium bicarbonate to water with Hydrilla plant increases photosynthesis rate by supplying more CO₂, a key reactant.
Adding sodium bicarbonate to water with Hydrilla plant increases photosynthesis rate by supplying more CO₂, a key reactant.
Photosynthesis Equation
6CO₂ + 6H₂O →light C₆H₁₂O₆ + 6O₂
Carbon dioxide often acts as the limiting factor in aquatic plant setups.
Option Analysis
a. It will remain unchanged
Incorrect – NaHCO₃ dissociates to HCO₃⁻ which releases CO₂ in water, raising concentration and boosting rate (unless already saturated).
Incorrect – NaHCO₃ dissociates to HCO₃⁻ which releases CO₂ in water, raising concentration and boosting rate (unless already saturated).
b. It will decrease
Wrong – Higher CO₂ availability accelerates Calvin cycle, increasing oxygen bubbles from Hydrilla.
Wrong – Higher CO₂ availability accelerates Calvin cycle, increasing oxygen bubbles from Hydrilla.
c. It will stop
Impossible – NaHCO₃ supports photosynthesis by mimicking atmospheric CO₂ supply.
Impossible – NaHCO₃ supports photosynthesis by mimicking atmospheric CO₂ supply.
d. It will increase
Correct – Experiments show more O₂ evolution with NaHCO₃, confirming CO₂ as limiting factor.
Correct – Experiments show more O₂ evolution with NaHCO₃, confirming CO₂ as limiting factor.
Experiment Setup
- Hydrilla twigs placed under funnel in beaker
- O₂ bubbles released and counted to measure rate
- NaHCO₃ added (0.05-5% concentration)
- Increased bubbling observed under light exposure
Demonstrates Blackman’s Law of Limiting Factors.
CSIR NET Relevance
- Tests understanding of photosynthesis limiting factors
- Common in NEET/CSIR/UGC NET exams
- Practice: Track bubble counts with varying NaHCO₃ levels
- Quantitative analysis of aquatic plant photosynthesis assays
Key Takeaway: NaHCO₃ → ↑CO₂ → ↑Photosynthesis Rate → ↑O₂ Bubbles
