Question

Design an experiment to demonstrate that carbon dioxide is essential for photosynthesis. Write the observation and conclusion of the experiment.

Answer 1

Step 1: Experimental Objective: To establish the necessity of carbon dioxide (CO₂) for plant photosynthesis.

Step 2: Plant Preparation – Destarching: Place a healthy potted plant in darkness for 48 hours. This depletes existing starch, ensuring any subsequent starch formation is a direct result of photosynthesis during the experiment.

Step 3: Experimental Setup: Enclose one leaf within a conical flask containing potassium hydroxide (KOH). KOH will absorb ambient carbon dioxide, creating a CO₂-deficient environment around this leaf. A separate leaf will remain exposed to the atmosphere as a control.

Step 4: Light Exposure: Position the plant in direct sunlight for several hours to facilitate photosynthesis.

Step 5: Starch Detection: Detach the KOH-enclosed leaf and the control leaf. Decolorize the leaves by boiling them in alcohol to remove chlorophyll. Soften the leaves by rinsing them in warm water. Apply iodine solution to test for the presence of starch.

Step 6: Outcome: The leaf enclosed with KOH will not exhibit a blue-black color change, indicating no starch production. The control leaf exposed to air will turn blue-black, signifying the presence of starch.

Step 7: Determination: The experiment validates that carbon dioxide is indispensable for photosynthesis. The absence of CO₂ prevents starch synthesis, as evidenced by the leaf deprived of carbon dioxide.