Question

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

Answer 1

Experiment:

• Take a healthy potted plant and keep it in darkness for 48 hours to destarch its leaves.
• Cover one of the leaves with a conical flask containing potassium hydroxide (KOH) solution. KOH absorbs carbon dioxide from the air inside the flask.
• Expose the plant to sunlight for a few hours.
• Pluck the covered leaf and a normal leaf. Boil both leaves in alcohol to decolorize them. Rinse them in warm water to soften and then test them for starch using iodine solution.

Observation:

• The leaf covered with KOH does not turn blue-black, indicating the absence of starch.
• The normal leaf turns blue-black, indicating the presence of starch.

Conclusion: Carbon dioxide is essential for photosynthesis as the absence of CO2 prevents the synthesis of starch.