Osmosis -a different experiment

W.A.F. HOPPER

Osmosis in school text-books is demonstrated with an experiment using animal membrane. Is it possible to use plant membranes in these experiments?

Let us find out.

i. Make a vertical section of an onion bulb. Peel off the membrane from one of the inner fleshly leaves. Place the onion membrane in water in a petri-dish.

ii. Cut a section of a ripe tomato. Peel off the skin (membrane). Place the tomato membrane in water in another dish.

iii. Take a fairly large grape and make an incision near where the stalk is attached. Extract the fleshy portion of the fruit and wash the skin thoroughly.

Select a clean glass tube that is open at both ends. It should be about 40 cm in length and about 0.5 to 1.0 in diameter. Smoothen the cut ends of the tube by rubbing them on a stone. If the edges are not smoothened out then the membrane may get punctured.

You will need:

Three such glass-tubes.

Three small glass beakers/bottles of water.

Concentrated glucose solution (glucose dissolved in water.) Pieces of thread.

Three wooden stands.

Tie the three membranes firmly to the cut ends of the three tubes with thread. Pour some glucose solution into a tube. Check for any leakage.

Pour equal amounts of glucose solution into the tubes. Keep them separately in the breakers containing water. Fix the tubes using the wooden stands.

Mark the initial levels of glucose solution in all the three tubes. Observe every 15 minutes. Compare the rate of osmosis taking place in the three different plant membranes.

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