Transpiration Lab
By: Tori Meyer
Intro:
The purpose of this lab is to determine if fewer leaves will cause less
transpiration. Transpiration is the process that water is evaporated into the
atmosphere from the plant surface. Water potential relates because it’s
when water flows from a high to low concentration, so the water potential in
the atmosphere is higher. The water leaving the roots must be replaces and
that’s driven by water potential. The stomata is the pore openings
underneath plant leaves that can open and close according to the metabolic
needs of the plant. They are the ports for exchange of oxygen and carbon
dioxide gas for photosynthesis, but also release excess water into the air.
Transpiration is the loss of water from the plant surface by evaporation. With
light, since guard cells contain chlorophyll, they produce sugar, which
reduces the water potential in them. In this lab, the amount of leaves is
being tested. Transpiration is effected because the leaves are the surface
that releases water. Since transpiration happens through the surfaces of the
plant and move from high to low, it will move from inside the plant, up to
the leaves and out of the plant. This experiment was based of the number of
leaves on each plant. The first plant had all leave, the second had ¾ of its
leaves, the third had half of its leaves, and the fourth plant had no leaves.
They stayed in the same temperature and were fed the same amount of
water at the beginning. The independent variable is the number of leaves
being cut off and the dependent variable is the percent change in mass.
Percent change in mass is measures my taking the daily mass minus the
initial mass all over the initial mass. It measures transpiration through the
loss of mass/transpiration because all was covered by plastic but the leaves.
The loss per day equals the rate of respiration. The constants are
temperature, type of plant, amount of time, amount of light and the amount
of water. The control is the plant with none of its leaves cut off. The negative
control is the plant with all of its leaves cut off. If the plant has a higher
number of leaves then more water will be able to transpire through percent
change in mass because without leaves transpiration cannot occur.
Procedure:
First, one must cut off all the leaves of one of the plants, then three
fourths the leaves of the next plant, and then half the leaves of the next
plant. One plant should have all of its leaves. Then water each plant equally.
After that, wrap the root of the plant is a plastic bag and tie it so the soil is
covered and just the leaves are showing. Weigh each plant. Over the next
four day, one must record the weight of each plant and then calculate
percent change in mass.
Results:
My DATA
Day 1(initial) Day 2
Day3
Day 4
Day5
All Leaves
155.52g
154.17g
152.56g
150.77g
149.82g
¾ leaves
157.66g
155.64g
153.60g
151.77g
150.714g
½ leaves
172.76g
171.11g
169.59g
168.15g
167.11g
No leaves
93.56g
90.98g
89.29g
88.14g
87.5g
CLASS DATA
Initial
Mass
(g)
Day
Control
Dark
Full Light
Limited Light
Light - 76 watt
Light - 100 Watt
Moist
Moist - Every
Other Day
Fan
Number of
Leaves
Tuesday Wednesday
Thursday
Friday
Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Average
100.7
178.6
147.4
155.5
131.2
133.7
-1.5
-0.7
-0.9
-0.9
-1.4
3.5
-0.3
-2.5
-1.6
-2.3
-1.9
-2.6
-2.9
-2.3
-3.4
-2.8
-3.2
-3.1
-3.7
-3.5
-3.3
-4.1
-3.5
-4.0
-3.7
-4.7
-4.2
-4.0
Group 1
Group 2
Group 3
Average
Group 1
Average
Group 1
Average
140.7
95.4
147.7
-0.9
-1.0
-1.0
-0.9
-1.7
-1.7
-2.3
-2.3
-1.7
-1.7
-1.9
-1.8
-4.8
-4.8
-4.0
-4.0
-2.5
-2.4
-2.6
-2.5
-7.5
-7.5
-5.6
-5.6
-3.2
-3.0
-3.3
-3.2
-9.0
-9.0
-6.7
-6.7
Group 1
Average
Group 1
Group 2
Average
Group 1
Average
Group 1
Average
Group 1
Average
122.9
-3.4
-3.4
-3.3
-2.7
-3.0
0.0
0.0
0.0
0.0
-6.6
-6.6
-5.7
-5.7
-7.4
-0.1
-3.7
-0.7
-0.7
-0.2
-0.2
-10.12
-10.1
-8.2
-8.2
-10.4
-7.0
-8.7
-0.7
-0.7
-0.5
-0.5
-11.34
-11.3
-10.4
-10.4
-12.0
-8.0
-10.0
-0.9
-0.9
-0.9
-0.9
-12.5
-12.5
-2.8
-1.28
-2.0
-2.2
-0.96
-1.6
-5.7
-2.58
-4.1
-4.1
-1.84
-3.0
-7.1
-3.74
-5.4
-5.6
-2.67
-4.1
-8.3
-4.39
-6.3
-6.9
-3.27
-5.1
129.9
-1.5
-3.5
-4.5
-5.3
93.56
-2.76
-2.1
-4.56
-4.0
-5.79
-5.1
-6.48
-5.9
5 Off - 1
1/4 off
Average
10 Off
1/2 Off
Average
No Leaves1
No Leaves
-2
Average
168.1
479.8
132.8
155.8
200.2
136.1
166.36
90.9
157.66
118.43
172.76
Number Of Leaves
3rd hour and 4th hour Averages
% change (mass in grams)
0.0
-1.0
0
1
2
3
4
5
Suculent 4 hr average 1/4 off
-2.0
Suculent 4 hr average 1/2 off
-3.0
-5.0
Suculent 4 hr average no
leaves
3 hr average 1/3 off
-6.0
3 hr average 2/3 off
-4.0
-7.0
3 hr average no leaves
-8.0
Days
4th Block Class Averages
0
1
2
3
% Change (Mass in Grams)
2.0
4
5
Control Average
Dark Average
Full Light Average
0.0
Limited Light Average
-2.0
Light - 76 watt Average
-4.0
Light - 100 Watt Average
-6.0
Moist Average
-8.0
Moist - Every Other Day
Average
Fan Average
-10.0
1/4 Leaves Off Average
-12.0
1/2 Leaves Off Average
-14.0
Days
No Leaves Off Average
The graphs show a decline in its trend and the more of a decline in
mass, the more transpiration that is occuring. The plants that had less
leaves seem to decline at a little faster rate. In the class data the plants with
exposure to more light declined at a faster rate. Errors that could have
occurred in the experiment are uneven amounts of water, or one bag had
more coverage of the soil than another.
Conclusion:
Since there is a decline in percent change in mass and that margin is
bigger in plants with less leaves that means they are not transpiring as
much. The hypothesis fits this conclusion because it states that the more
leaves the more transpiration will occur. The control was the plant with all
leave and if you compare that to the plants with half or three quarter
amount the leaves, it show that the there is a faster decline rate. The plastic
bag that was put onto the plant disrupted water potential, but the plant with
all its leaves had better water potential. That is so because it had its full
stem and leaves where water could go to transpire. A closed stomata stops
transpiration and when water is short that is advantage because it will loose
less water. The disadvantages though are that water is pulled up the xylem
by pressure from the roots at a much slower rate. Also the plant cannot get
carbon dioxide that it uses for photosynthesis. Plants have adaptions the
reduce water loss. One is the cuticle. The cuticle is a secretion that
surrounds the epidermis of the leaves. It reduces water loss if a leaf has a
thick waxy cuticle then since the lipids and fats are hydrophobic to water,
this prevents evaporation and thus slows transpiration. Also the shiny
surface reflects some sunlight which can reduce heat at the surface reducing
evaporation further. Another is thicker or thinner leaves and hair on leaves.
The percent of water loss each day needed to be calculated to show the
average of water loss. The transpiration pull relates to hydrogen bonding
because of the property of the water molecules that cling to each other and
pull it up the xylem. The water moves up the plant, enters the This lab could
be modified to be better by adding more time to the leaves, moves into air
spaces in the leaf, and then evaporates through the stomata. experiment.
Over time is when you can see more changes and maybe add water again
and see how the plant reacts.
 Water molecules in the xylem.