Plant Transpiration Lab

Data Table

 

	Normal	With Fan	With Heater	With Lamp
Arrowhead	3.6	7.5	6.6	4.0
Coleus	0.9	6.0	3.9	3.0
Devil’s Ivy	2.9	4.6	4.1	3.0
Dieffenbachia	4.1	7.7	6.0	3.9
English Ivy	1.8	5.1	3.2	2.1
Geranium	1.2	4.7	5.8	2.4
Rubber plant	4.9	8.4	6.8	4.3
Weeping Fig	3.3	6.1	4.9	2.5
Zebra Plant	4.2	7.6	6.1	3.2

Calculations 


The numerical effect of the wind (fan) on each plant
 

Arrowhead: 7.5-3.6 = +3.9
Coleus: 6.0-0.9 = +5.1
Devil's Ivy: 4.6-2.9 = +1.7
Dieffenbachia: 7.7-4.1 = +3.6
English Ivy: 5.1-1.8 = +3.3
Geranium: 4.7-1.2 = +3.5
Rubber Plant: 8.4-4.9 = +3.5
Weeping Fig: 6.1-3.3 = +2.8
Zebra Plant: 7.6-4.2 = +3.4

Average: +3.42 (The wind had a positive effect, increasing the average transpiration rate of the plants by 3.42)



The numerical effect of the heat (heater)

Arrowhead: 6.6-3.6 = +3.0
Coleus: 3.9-0.9 = +3.0
Devil's Ivy: 4.1-2.9 = +1.2
Dieffenbachia: 6.0-4.1 = +1.9
English Ivy: 3.2-1.8 = +1.4
Geranium: 5.8-1.2 = +4.6
Rubber Plant: 6.8-4.9 = +1.9
Weeping Fig: 4.9-3.3 = +1.6
Zebra Plant: 6.1-4.2 = +1.9

Average: +2.28 (The wind had a positive effect, increasing the average transpiration rate of the plants by 2.28)


The numerical effect of light (lamp)

Arrowhead: 4.0-3.6 = +0.4
Coleus: 3.0-0.9 = +2.1
Devil's Ivy: 3.0-2.9 = +0.1
Dieffenbachia: 3.9-4.1= -0.2
English Ivy: 2.1-1.8 = +0.3
Geranium: 2.4-1.2 = +1.2
Rubber Plant: 4.3-4.9 = -0.6
Weeping Fig: 2.5-3.3 = -0.8
Zebra Plant: 3.2-4.2 = -1.0

Average: +0.17 (the light had a marginal positive effect, increasing the average transpiration rate of the plants by 0.17)


Therefore, the wind, followed by heat and light, had the biggest impact on the plants' transpiration rate.  

Journal analysis questions

1.     Describe the process of transpiration in vascular plants.

 

In vascular plants, water is absorbed through the roots and carried upward through the stem to the leaves. Some of the water absorbed by a plant's roots is used for photosynthesis, but much is lost to the environment by evaporation through stomata.  This process is called transpiration.

 

2.     Describe any experimental controls used in the Investigation.

 

In a laboratory, a plant's transpiration rate can be measured using a potometer.

To measure transpiration rate, a plant sprig is mounted on the potometer and the burette and pipette are filled with water. Over time the plant will transpire and absorb water through its stem. The potometer is constructed in such a way that the plant's water source is the pipette, therefore the amount of water transpired over time can be determined by reading the water level in the pipette after time has passed. The water supply in the pipette can be replenished from the water supply in the burette by releasing the pinch clamp.

 

3.     What environmental factors that you tested increased the rate of transpiration? Was the rate of transpiration increased for all plants tested?

 

Wind and heat increased the rate of transpiration for all plants tested.

Light, however, increased the transpiration rate for some plants, and decreased the rate for others.

 

4.     Did any of the environmental factors (heat, light, or wind) increase the transpiration rate more than the others? Why?

 

Wind increased the transpiration rate more than heat and light did.

This is somewhat related to the relative humidity of the air, in that as water transpires from a leaf, the water saturates the air surrounding the leaf. If there is no wind, the air around the leaf may not move very much, raising the humidity of the air around the leaf. Wind will move the air around, with the result that the more saturated air close to the leaf is replaced by drier air.

 

 

5.     Which species of plants that you tested had the highest transpiration rates? Why do you think different species of plants transpire at different rates?

 

Rubber plant showed the highest transpiration rate. This is primarily due to its leaves with a bigger surface area. Varying transpiration rates according to different species are the result of adaptation to climate. Some plants which grow in arid regions, such as cacti and succulents, conserve precious water by transpiring less water than other plants.

 

6.     Suppose you coated the leaves of a plant with petroleum jelly. How would the plant's rate of transpiration be affected?

 

As petroleum jelly tends to hinder water from evaporating, the transpiration rate will drop abruptly.

 

7.     Of what value to a plant is the ability to lose water through transpiration?

 

Transpiration cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients and water from roots to shoots.