Experiments/activities

An Experiment to Prove that Translocation of Water Takes Place Through Xylem and Food Materials Through Phloem:

Requirements:

• A twig, an empty jam jar, blue/violet food colour, water

Procedure:

• Phloem is present near the bark of the trunk, so remove the bark all round. Do it carefully so that xylem tissues do not get damaged.
• Fill the jam jar three-fourths with water.
• Add a few drops of blue/violet food colour to the water.
• Place the twig in this water.
• Record observations over a period of five days.

Observation:

• Faint flecks of colour are observed on the leaves gradually over the period of five days.
• If a cross-section of the stem is cut, tubes coloured with blue/violet can be seen towards the centre of the stem.
• This is where xylem is present.
• The leaves above the ring look fresh and green.
• The portion below the ring withers.
• The portion just above the cut ring grows in diameter.

Conclusion:

• The leaves look fresh because they continue to get water and minerals.
• This is because the xylem is intact.
• The section of the plant just below the cut portion starts withering because the phloem has been cut and thus the supply of food to that portion has stopped.
• Because the phloem is cut, the portion above the cut increases in diameter as the food gets collected there.
• This shows that xylem transports water and minerals, and phloem translocates food materials.

An Experiment to Demonstrate How Substances Move Through A Semi-Permeable Membrane, Like In Dialysis:

Requirements:

• A thistle funnel, a beaker of water, sugar solution, a clamp stand, a piece of thread, an egg membrane or cellophane paper

Procedure:

• Take some concentrated sugar solution in a thistle funnel and cover the mouth of the thistle funnel with an egg membrane (a membrane enveloping an egg and clearly visible after boiling it) and tie it with thread.

Egg membrane

• Invert this funnel arrangement in a beaker of water.
• Mark the level of sugar solution in the funnel.

Observation:

• The level of liquid in the thistle funnel will rise.

Conclusion:

• This is because the egg membrane is semi-permeable i.e. it allows only the solvent molecules to pass from its higher concentration (water in the beaker) to its lower concentration (in the thistle funnel) and does not allow molecules of the solute to pass through it.
• This is how solvent molecules move in dialysis.

An Experiment to Demonstrate Transpiration:

Requirements:

• A potted plant, a polythene bag, a glass jar.

Procedure:

• Place the plant in the pot, and enclose the soil of the pot in a polythene bag.
• Now cover the plant with a glass jar.
• Leave it undisturbed for some time.

Observation:

• We will notice tiny droplets of water on the inner surface of the glass cover.

Conclusion:

• The water comes from the leaves, since the soil has been covered completely.
• This shows that plants give out water vapour through transpiration.