The Effect of Air Movement on the Rate of Transpiration

THE EFFECT OF AIR MOVEMENT ON THE RATE OF TRANSPIRATION Objective : To study the effect of air movement on the rate of transpiration. Problem Statement : How does air movement affect the rate of transpiration? Hypothesis : In still air, the rate of transpiration is low, in fast moving air, the rate of transpiration is high. Variables : (a) Manipulated variable : Air movement (b) Responding variable

: Rate of transpiration// Time taken for the air bubble to move a distance of 10 cm

(c) Controlled variable

: Type of plant// Distance of 10 cm

Apparatus and Materials : Potometer, stopwatch, ruler, knife, rubber stopper with holes, tissue paper, fan, basin, Hisbiscus plant, vaseline and water . Technique : By measuring the time taken for the air bubble to move from P to Q// a distance of 10 cm by using a stopwatch and a potometer.

Procedure :

1.

Potometer was immersed in water to remove air bubbles.

2.

The screw clip was opened to fill the capillary tube with water.

3.

The branch of the plant was cut in the water.

4.

Thr end of branch was pushed through the hole in the rubber stopper under water.

5.

A beaker of water was placed at the end if the capillary tube.

6.

The screw clip was closed and the potometer was removed from the water.

7.

The surface of the leaves and stems was wiped with tissue paper.

8.

Vaseline was spread around every joint to ensure that they are airtight.

9.

The potometer was left aside until the air bubble in the capillary tube move steadily.

10. Two points, P and Q, of length 10 cm apart were marked on the capillary tube. 11. The time taken for the air bubble to move from P to Q was recorded. 12. The position of the air bubble was reset at point P by opening the screw clip. 13. Steps 11 and 12 were repeated twice and the mean time was calculated. 14. Steps 11 to 13 were repeated by placing the potometer below a moving fan. 15. The rate of transpiration was calculated by using the following formula : Rate of transpira tion =

10 cm/ minute t

Where t = time taken for air bubble to move from P to Q

Results :

1

2

3

Mean

Rate of transpira tion, 10 cm min -1 t

Still air

20.0

18.5

19.5

19.3

0.52

Fast moving air

1.6

1.9

1.6

1.7

5.88

Air Movement

Time/ minute

Discussion : 1.

Why the branch of the plant be cut in water? -

To prevent air bubble from going inside the xylem vessels.

-

The present of trapped air bubble inside the xylem vessels will interupt the capillary movement of water by producing air column inside the xylem vessels.

2.

What is transpiration? Where does it occur? -

Transpiration is the process of evaporation of water vapour from plants to the atmosphere.

3.

It happen through stomata, lenticels and cuticles.

How does transpiration occur through stomata? -

Water evaporates from the mesophyll of a leaf producing water vapour which accumulated in the intercellular spaces between the layers of mesophylls.

-

When the spaces are saturated with water vapour, a concentration gradient creates between the intercellular spaces and the atmosphere.

4.

Hence, water vapour moves from the leaf to the atmosphere.

State two reasons why transpiration is important. (a) To establish a transpiration pull for the roots to absorb water and mineral ion from the soil to be sent to the leaves. (b) To cool the plant in hot weather.

Conclusion : The hypothesis is accepted. The rate of transpiration is high in fast moving air, while the rate of transpiration is low in still air.