EXPERIMENT

DATE

TOPIC

AIM

APPARATUS

PROCEDURE

#1

19-0CTOBER-2011

Transpiration

To investigate the effects of certain factors on the rate of transpiration.

Leaves with petiole, electric balance, stopwatch, retort stands, string, fan, Vaseline, pin, polystyrene cement, paper clips, microscope, anhydrous cobalt chloride paper

1) Several leaves with petiole intact were removed from a plant. The leaves were strung together and weighed, with an attempt being made to get a mass of just about 10g.

2) The time was noted and the leaves hung in such a way so as to not touch one another under 3 conditions: still air, turbulent air from a fan and with both leaf surfaces smeared with Vaseline.

3) The leaves were reweighed at 15 minute intervals for 4 more readings.4) The percentage decrease in weight at each interval was calculated using

the formula: percentage decrease= [(a-b)*100]/a where a=initial weight at the beginning of the experiment b=new weight

5) A strip of anhydrous cobalt chloride paper was applied to the upper and lower surfaces of and intact leafy shoot. The paper was held firmly in place by glass slides and paper clips.

6) The number of stomata on a given area of a leaf was determined by making a polystyrene replica of the leaf surface by simply spreading the polystyrene cement thing over the surface with a pin then dry peeling off this cement then observing under a microscope at medium power.

7) A transparent ruler was used to measure the diameter of the observed field.

RESULTS

Table showing change in mass of leaves with time in a transpiration experiment

A B CTime (mins) Mass of leaves in still

air (g)Mass of leaves in turbulent air (g)

Mass of leaves with Vaseline (g)

0 10.50 10.25 11.9315 10.24 9.95 11.9130 10.01 9.85 11.7945 9.75 9.76 11.64

60 9.40 9.70 11.58

Table showing stomata count for upper and lower surfaces of a leaf

UPPER SIDE

UPPER SIDE

UPPER SIDE

LOWER LOWER LOWER

Area 1st 2nd 3rd 1st 2nd 3rdNumber of

stomata500 480 500 800 900 900

Area (mm2) 63.6 63.6 63.6 63.6 63.6 63.6Amount per

unit area(no./mm2)

7.86 7.55 7.86 12.58 14.15 14.15

When cobalt chloride was used on the leaves, the upper surfaces changed the blue paper to pink at a slower rate than the lower surface did.

CALCULATIONS

Percentage change AFor A between 0 and 15 min =[ (10.50-10.24)*100]/10.50 =2.48%Between 15 and 30 min =1.37% Between 30 and 45 mins= 2.60% Between 45 and 60 min= 3.59%Overall % change= 10.04%

Percentage change BFor B between 0 and 15 min= [(10.25-9.95)*100]/10.25 = 2.92%Between 15 and 30 min=1.01%Between 30 and 45 mins=0.91%Between 45 and 60 min= 0.62%Overall % change= 5.46%

Percentage change CFor C between 0 and 15 min= [(11.93-11.91)*100]/11.93 = 0.12%Between 15 and 30 min=1.01%Between 30 and 45 min=1.27%Between 45 and 60 min= 0.52% Overall % change= 2.92%

Area= ∏r2 r=9mm hence area= 63.6mm2

DISCUSSION Transpiration is the evaporation of water from the leaves of plant. The rate of transpiration is not constant. The rate varies with varying environmental factors. This experiment served to investigate the effects of certain factors on the rate of transpiration; wind speed, thickness of waxy cuticle and no wind.

CONCLUSION

The number of stomata present also affects the rate at which transpiration occurs.By theory, the greater the wind speed, the greater the rate of transpiration since the wind would remove the extra water from the surroundings creating a gradient between the leaves and the atmosphere. With a thicker waxy cuticle guarding the leaf surface, it is expected that the level of transpiration would decrease since this factor would inhibit the amount of water exiting the plant. Transpiration levels also decrease with increasing humidity, increase with increasing temperature and increasing light intensity. As water is lost from the leaves, a deficit is then created hence more water is pulled up to fill the space by capillarity; creating what is known as a transpiration stream.The experiment proved to be problematic as all the expected results weren’t present; seeing that the percentage change in mass was lesser in turbulent wind than in still air when the results expected based on theory was vice versa.The percentage change when Vaseline was present was however lesser than that without vaseline as expected. The vaseline served as a cuticle size increaser and hence prevented too much water from escaping from the plant leaves hence, the percentage change in mass was smaller.As seen by the experiment, increasing the number of stomata increases the level of transpiration and hence the level of water loss. This was demonstrated in the relatively quick time taken for the blue cobalt chloride paper to become pink when place on the lower surface which had a greater number of stomata in comparison to the time taken to change on the upper surface which was proven to have less stomata.The problems in the experiment which caused the deviation in results could be due to improper use of the equipment. Due to the reduction in forces pushing up the water to replace that evaporated, the inconsistent results obtained for the turbulent wind system could have been due to such.

Transpiration of water from the leaves of plants is affected by several factors including cuticle thickness, presence of wind and number of stomata as demonstrated in this experiment. The systems can either reduce or increase the transpiration rate.