Demonstration Of Physiological Experiments

Demonstration of Physiological Experiments 1. Curling Experiment: This experiment demonstrates the process of osmosis. For this experiment three Petri dishes are taken containing water, concentrated sugar solution and concentrated salt solution respectively. Equal length pieces of arum petiole are taken and slits are introduced at the either end. One piece is kept in each Petri plate for 15-20 min. The piece of arum petiole in Petri plate containing water shows curing at both the ends and slits open. The water molecules are more in the Petri plate than in the parenchymatous cells of arum petiole. Due to endosmosis water enters the cells and the inner cells become turgid and curling occurs at both the ends of petiole. No curling is seen in the arum pieces kept in Petri plates containing concentrated sugar and salt solution. This is because there are relatively more water molecules in the parenchymatous cells of arum petiole than the Petri plates containing concentrated solutions. Therefore water moves from the cells in to the Petri plate by the process of exo-osmosis and slit in the arum petiole does not open. 2. Imbibition pressure experiment: Taking up water and consequent swelling of colloidal matter and other substances is called imbibition. Due to this there is an increase in the volume of material and this swelling exerts an outward pressure called imbibition pressure. A glass jar is fitted with air tight cork. Dry seeds are placed in the jar and water is sprinkled on the seeds. The pointer is adjusted to zero on the scale. The apparatus is kept undisturbed for few hours. The seeds absorb water and they swell or imbibe. Due to swelling volume of the seeds increase and imbibition pressure is developed in the jar and the pointer moves on the scale accordingly. The size of the seeds increases because the testa has colloidal substances. 3. Arc indicator: Growth is a permanent and irreversible change. Growth is greatest at the stem tip. It is a continuous elongation of the plant which can be measured by the arc indicator. A thread is tied to the stem tip. It is passed over a pulley of arc indicator, to which a long pointer is attached. The tread is kept tight by means of weight. During growth of the twig, the stem elongates and the weight moves down. The pulley also moves which is indicated by a pointer on a scale of a graduated arc. The movement of needle is directly proportional to the growth rate of the plant. By recording the movement of pointer in angular degrees, the growth rate of the plant can be measured. 1 angular degree = π/180 = 3.14/180 To convert into linear growth=3.14/180 × radius of an arc (-- cm). 4. Effect of root promoting hormone: Auxins are one of the important phytohormones essential for growth and development of plants. Auxins are synthesised at the growing apices. In artificial vegetative plant propagation, auxin treatment is given in low concentration which promotes root formation.

1

A girdle is prepared at the internodal region of a plant twig and small quantity of lanoline paste with auxin is applied at the girdled region of the stem. The girdle portion is then covered with moist moss kept in position with the help of polythene sheet. After few days, roots are formed at the girdle. 5. Effect of gibberellic acid (GA) on germination of seeds: Gibberellins are plant growth regulators found in higher plants. Effect of GA can be demonstrated using following experiment. The seeds of Phaseolus are pre-soaked for 4-5 hrs in different solutions of GA. The seeds soaked in water for the same duration serve as control. After the treatment, the seeds are thoroughly washed in running tap water and then layered on a moist germination paper in the Petri plates. It is observed that the exogenously applied GA breaks the dormancy of seeds and promotes germination. 6.

Suction pressure due to transpiration:

Water is continuously evaporated from the aerial parts of the plant due to transpiration and this loss of water by aerial organs is compensated by the water absorbed by the roots due to suction force or pulling force. A vertical glass tube is fixed on a stand. The lower end of the tube is kept in a Petri plate containing mercury. The tube is filled with water and a small twig of a plant is inserted at the other end. This end of the tube is made air tight. The apparatus is kept in the sunlight. After some time the mercury starts rising in the glass tube. *****

2