Class X Practical: Plant Life - Photosynthesis

Objective

To demonstrate the necessity of light, carbon dioxide, and chlorophyll for starch production during photosynthesis, and to show the release of oxygen during the process.

Guidelines

1. Necessity of Light for Starch Production

1. Setup: Destarch a potted plant by keeping it in the dark for 2-3 days. Cover a part of one leaf with a black paper or aluminum foil (using clips) and expose the plant to sunlight for 6-8 hours.
2. Starch Test: Remove the leaf, remove the cover, boil the leaf in water, then in alcohol (in a water bath) to remove chlorophyll. Wash the leaf and perform an iodine test.
3. Expected Outcome: The uncovered part of the leaf will turn blue-black (presence of starch), while the covered part will remain yellowish-brown (absence of starch), proving light is necessary for photosynthesis.

2. Necessity of Carbon Dioxide for Starch Production

1. Setup: Destarch two potted plants. Place one plant under a bell jar with a watch glass containing KOH solution (absorbs CO₂). Place the other plant under a bell jar with a watch glass containing plain water (control). Seal the bell jars to the ground. Expose both setups to sunlight for 6-8 hours.
2. Starch Test: Perform an iodine test on a leaf from each plant as described above.
3. Expected Outcome: The leaf from the plant in the KOH setup will show no starch, while the control plant's leaf will show starch, proving CO₂ is necessary for photosynthesis.

3. Necessity of Chlorophyll for Starch Production

1. Setup: Take a variegated leaf (e.g., from Croton or Coleus plant) that has green (chlorophyll) and non-green (no chlorophyll) areas. Expose the plant to sunlight for 6-8 hours.
2. Starch Test: Perform an iodine test on the variegated leaf as described above.
3. Expected Outcome: Only the green parts of the leaf will turn blue-black, while the non-green parts will remain yellowish-brown, proving chlorophyll is necessary for photosynthesis.

4. Release of Oxygen using Hydrilla/Elodea

1. Setup: Place a sprig of Hydrilla or Elodea in a beaker containing pond water. Invert a test tube filled with water over the plant, ensuring the stem of the plant is inside the test tube.
2. Exposure: Place the setup in bright sunlight.
3. Observation: Observe the bubbles evolving from the cut end of the plant and collecting in the inverted test tube.
4. Gas Test: After a sufficient amount of gas has collected, carefully remove the test tube and insert a glowing splint into it.
5. Expected Outcome: The glowing splint will rekindle, confirming the presence of oxygen gas, thus demonstrating that oxygen is released during photosynthesis.