Experiments/activities

EXPERIMENTS/ACTIVITIES

(1) An Experiment to Show That Only Green Plants Can Photosynthesise:

Requirements:

A Coleus leaf (variegated- leaf with two colours), beaker, beaker stand, Bunsen burner, water, test tube, ethanol, and iodine solution

Procedure:

Place a beaker about three-fourths full of water on a stand and boil the water. Place the Coleus (variegated) leaf in this water for about two minutes. (This will break down the cell walls.)
Take the Coleus (variegated) leaf out and put it in a test tube with three-fourths alcohol. Place this test tube in very hot water for about ten minutes. As alcohol warms up, it will remove chlorophyll from the leaf and make it almost colourless.
After about ten minutes, remove the Coleus leaf and dip it in warm water briefly to soften the leaf.
Now place the leaf on a white tile and add 3-4 drops of iodine solution.

Observation:

Only the green portion of the leaf turns bluish-black while the non-green portion does not.

Conclusion:

(2) An Experiment to Show That Light Is Necessary For Plants:

Requirements:

Procedure:

Cover a part of a leaf using strips of black paper.
Destarch the plant by placing it in a dark corner for 3 days.
Pick a leaf from the destarched plant and test it for starch to confirm whether it is fully starch-free.
Now place the plant in strong sunlight for at least 6 hours.
Pick the leaf covered by the strip of black paper, remove the strip and test the leaf for starch.

Observation:

Conclusion:

There was no starch formation in the covered part of the leaf so this part did not turn blue-black. This shows that light is necessary for photosynthesis.

(3) Experiment to Show That Carbon Dioxide Is Necessary For Plants:

Requirements:

A potted plant, sodium hydroxide crystals, a conical flask with a split cork, iodine solution, and a dropper

Procedure:

Keep the potted plant inside a dark room for a few hours. Water it.
Now put some sodium hydroxide crystals inside a conical flask. This absorbs carbon dioxide of the air.
Place one of the leaves (without breaking it from the plant) inside the flask and cork it. (Leaf X- Leaf with cork, Leaf Y- Leaf without cork)

Now, keep the entire arrangement out in the sunlight.
After a few hours, test the leaf inside the conical flask and any other leaf of the plant for starch, using iodine solution.

Observation:

The leaf that was clasped inside the conical flask does not turn iodine solution bluish-black. The other leaf turns iodine bluish-black.

Conclusion:

The leaf inside the conical flask did not carry out photosynthesis. This is because there was no carbon dioxide available to it.