How does Elodea living in the light affect the pH of the solution? What does this imply about what process plants carry out in the light and why?
The correct answer and explanation is:
Correct Answer:
When Elodea lives in the light, the pH of the solution increases. This indicates that photosynthesis is occurring, which consumes carbon dioxide from the water.
Explanation:
Elodea is an aquatic plant that performs photosynthesis in the presence of light. During photosynthesis, the plant absorbs carbon dioxide (CO₂) and uses light energy to produce glucose and oxygen. The general equation for photosynthesis is:
6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂
Carbon dioxide dissolves in water to form carbonic acid, which lowers the pH of the solution. The chemical equilibrium is:
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
When Elodea is exposed to light, it actively removes CO₂ from the water to use in photosynthesis. As the CO₂ concentration in the solution decreases, the equilibrium shifts to replace the missing CO₂, which leads to the consumption of hydrogen ions (H⁺). This results in a decrease in the concentration of H⁺ ions, making the solution less acidic and therefore increasing the pH.
The increase in pH when Elodea is in the light clearly shows that photosynthesis is happening. This process only occurs in the presence of light because it depends on light energy to drive the conversion of carbon dioxide and water into glucose and oxygen. The rise in pH serves as evidence that carbon dioxide is being used up, reducing the acidity of the environment.
This experiment helps confirm that plants like Elodea carry out photosynthesis in the light and that this process directly influences the chemical composition of the surrounding environment, specifically by raising the pH due to the removal of carbon dioxide.