Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
Transpiration Lab
Introduction:
In this experiment we will be observing the effect that different exposure to light will
have on a plants transpiration rate. Before conducting our experiment, the group came to
a consensus and stated that the plant without any exposure to light will have the lowest
transpiration rate given that there will be a lack of photosynthesis conducted without the
needed light and the plant exposed to light continuously will have the highest
transpiration rate, meaning that the water will escape the stomata at a quicker rate than
any of the other.
To test this theory, our control will be a plant placed in a window seal to receive the
“normal” 24 hour cycle of day light and darkness, unlike our two experimental locations
where one plant will be placed under a lamp 24/5 and the other in a dark cabinet. In order
to determine which plant transpired the most, we will take the weight the initial plant’s
weight after lightly bathing them with water, then take their weight daily. The difference
between the initial weight and final weight will indicate the total water loss; to divide the
difference by the total amount of days will indicate the rate of transpiration per day.
Control: Plant exposed to normal 24hr cycle of light
Experiment Group A: continuous exposure to light
Experiment Group B: no exposure to light of any kind
Hypothesis
Null: All three plants will have the same transpiration rate.
Experimental: The plant that receives less light will have the lowest transpiration rate; the
plant that receives constant light will have the highest transpiration rate, while our control
will be the neutral respiration to give a basis for each contrasting light exposure.
Materials:
1.
2.
3.
4.
5.
6.
Three plants (Pansy)
Normal Sunlight
Artificial light (Lamp)
Darkness (a Cabinet or Dark Closet)
Clear plastic wrap
Water
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
7. Rubber band
8. Thermometer
9. Pen/Permanent Marker
10. Paper to record results
11. Tape
12. Scale
Procedures:
1.) Remove the plants from the plastic carton and lightly water (bathe) the soil
and cover with clear plastic wrap.
2.) Label each plant as Group A (continuous light), Group B (no light) and
Control.
3.) Weigh each plant individually and record the initial weight (g) on the label.
4.) Then place control in a window seal, one under a lamp and the other plant in
complete darkness.
5.) Leave plants under these conditions for 5 days, while periodically checking
the weight of the plant daily and recording the results.
Collected Data:
Plants Weight over the Course of Five Days with Various Light Exposures
Group
Day 1
Day 2
Day 3
Day 4
Day 5
Group A
38.21g
32.83g
29.22g
25.62g
20.19g
Group B
42.70g
43.75g
41.37g
38.99g
30.80g
Control
46.83g
42.77g
39.48g
36.20g
30.42g
Rate of Transpiration
Formula: Initial Weight – Final Weight/Days of Exposure
Rate of Transpiration is the amount of water lost through the stomata (g)
Group
Rate per day
Group A
3.604g
Group B
2.38g
Control
3.282g
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
Data Displayed in Charts & Graphs:
Plants Weight over Course of Five Days
50
45
40
35
Day 1
30
Day 2
25
Day 3
20
Day 4
15
Day 5
10
5
0
Group A
Group B
Control
Analysis of the Plants Weight over the Course of Five Days with Various Light
Exposures:
Our data shows that on day one, our group A plant had a weight of 38.21 grams, our
group B plant had a weight of 42.70 grams and our control group plant had a weight of
46.83 grams. By day two, our group A plant weight had decreased by 5.38 grams, our
group B plant weight had increased by 1.05 grams and our control group plant weight had
decreased by 4.06 grams. By day 3, our group A plant weight had decreased by another
3.61 grams, our Group B plant weight had decreased by 2.38 grams, and our control
group plant weight had decreased by 3.29 grams. By day four our group A plant weight
had decreased by another 3.60 grams, our group B plant weight had decreased by another
2.38 grams and our control group plant weight had decreased by another 3.28 grams. By
Day 5, our group A plant weight had decreased by another 5.43 grams, our group B plant
weight had decreased by 8.19 grams and our control group plant weight had decreased by
5.78 grams. In all, our group A plant weight decreased by a total of 18.02 grams, our
group B plant weight decreased by a total of 11.9 grams, and our control group plant
weight decreased by a total of 16.41 grams. As expected our group A plant showed the
most weight loss—implying that a higher transpiration rate was found in it because of it’s
continuous exposure to the light. Our group B plant showed the least amount of weight
loss—implying that a lower transpiration rate was found in it because of its continuous
lack of exposure to light. Because it was exposed to no light, it wasn’t easily dried out
and therefore retained its water for a longer time. Also as expected, our control group
plant showed a weight loss that was somewhere in between the weight loss of group A
and group B. It’s transpiration rate, in comparison to that of group A and group B, was
somewhere between theirs as well since the control group plant had times of exposure to
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
the light as well as times of no exposure to the light. In our data, the group B plant is the
only plant that experienced an increase in weight at any time during the experiment. This
increase was found on day 2—its weight increased by 1.05 grams. Whenever the weights
decreased, we knew that the plant(s) lost water through transpiration. The one time the
weight did increase, we know the plant did gain weight possibly from increased water
weight but we had no solid proof to show that.
As far as errors go in our experiment—we weren’t able to collect the stomata samples
from the leaves using the clear nail polish. We attempted but failed. When we put the
polish on our leaves, the leaves broke. Once we were successful in getting the dried nail
polish off our plant and under the microscope—but the microscope showed no stomata.
Apart from that the only other complication that can be singled out is the tightness of the
ceramic wrap on each plant’s soiled roots. There’s a possibility that the tightness of the
wraps may have had some impact on the transpiration rates. Also, the fact that we had to
bring our group B plant into the light in order to collect data could have impacted it’s
transpiration rate. The group B plant did have some exposure during those times of data
collecting—but that’s it. Other than these errors, our experiment ran smoothly and didn’t
have any other major complications.
Further experimentation is encouraged in order to see if the data of these experiments will
be consistent with the ones found in this one.
Rate of Transpriation
4
3.5
3
2.5
2
Rate of Transpriation
1.5
1
0.5
0
Group A
Group B
Control
Analysis of the Plants Rate of Transpiration:
Based on the data collected over the five day period plant A(under lamp) had a higher
daily rate of transpiration than plant B(in cabinet).
With group B in comparison to the control grouped the rate of transpiration day to day
wasn't to far off. Day one only a difference of 4.13g of transpiration while you compare
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
group A and controlled group their is a 8.62g difference in transpiration. Day two, the
difference in group B and controlled group is minimized to a margin of only 0.98g while
group A holds a even bigger margin of difference than it did the day before. By day three
the difference between group B and the control groups rate of transpiration is 1.89g while
there is a 10.26g difference between group A and the control group. With this trend
continuing further into time, it's suggested that no light exposure and natural growth and
light exposure show similarities in plants ability to adaption, while group A was effected
by over exposure to light causing a dramatic increase in the transpiration rate.
Conclusion:
Our hypothesis was proven correct with our inference that the plant exposed to more light
would have the highest rate of transpiration even if it is only 0.322g more than our actual
control. Our hypothesis was also correct with the inference that the plant that didn’t
receive any source of light would have the lower transpiration rate being 0.902g lower
than the control and 1.224g less than our experimental Group A. Unfortunately we were
unable to successfully identify the amount of stomata to make further connections
between light and transpiration rate, we now understand the skill in correctly completing
the task to obtain an accurate result. It seems that there might have been some other
factors that came into play—as stated above in our analysis—and do encourage further
experimentation to be conducted. All in all, our hypothesis for this experimentation was
proven correct by our data and our predictions on the comparisons between the
transpiration rates of the group A plant, group B plant and control group plant were
correct.
Step 1 a-h:
a.
How can you calculate the total leaf surface area expressed in cm2? In
mm2?
Lay the leaves to be measured on a 1-cm grid and trace their outlines.
Count the number of square centimeters. To get in mm2, convert from cm2
to mm2 by multiplying the number of centimeters by 10. 1cm=1=mm.
b.
How can you estimate the leaf surface area of the entire plant without
measuring every leaf?
You can measure one leaf and multiply the surface area of that leaf by the
number of leaves on the plant.
c.
What predictions and/or hypotheses can you make about the number of
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
stomata per mm2 and the rate of transpiration?
The more stomata found per mm2 in the plant leaves, the more pores
available for transpiration. If there are more stomata found, then the
transpiration rate will probably be extremely high. If there are less stomata
found, less transpiration can occur.
d.
Is the leaf surface area directly related to the rate of transpiration?
The stomata on the underside of the leaf regulate transpiration. The
leaf surface area helps to estimate the number of stomata, which could
speed up or slow the rate of transpiration.
e. What predictions can you make about the rate of transpiration in plants
with smaller or fewer leaves?
Plants with smaller/fewer leaves have less stomata available to the plant for
transpiration so possibly the rate of transpiration also varies with the
amount or size of the leaves on the plant.
f.
Because most leaves have two sides, do you think you have to double
your calculation to obtain the surface area of one leaf? Why or why
not?
You have to double your calculations of a leaf's surface area. The surface
area includes the total area of ALL SIDES of an object so in order to
calculate the total surface area, you must calculate the surface area of both
sides of the leaves.
g.
Water is transpired through stomata, but carbon dioxide also must
pass through stomata into a leaf for photosynthesis to occur. There is
evidence that the level of carbon dioxide in the atmosphere has not
always been the same over the history of life on Earth. Explain how the
presence of a higher or lower concentration of atmospheric carbon
dioxide would impact the evolution of stomata density in plants.
The higher carbon dioxide is in the atmosphere the lower the amount of
stomata because plants can get all the carbon dioxide needed using a small
amount of stomata in this environment. The lower the carbon dioxide is in
the atmosphere, the higher the amount of stomata because plants will need
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
more stomata to get enough carbon dioxide in this environment. This
affects the plants evolutionarily in that they can decide when they need
more stomata and when they need less stomata depending on the conditions
of their environment.
h.
Based on the data in the following table, is there a relationship between
the habitat (in terms of moisture) to which the plants are adapted and
the density of stomata in their leaves? What evidence from the data
supports your answer?
There is a relationship. Plants, like the water lily, who live in very moist
places, get their water from beneath their leaves. Because of this they can
use the stomata on the upper, top, part of their leaf for other things such as
transpiration, photosynthesis, etc.
Getting Started Questions…
1. If the plant cell has a higher solute potential/concentration than it’s surrounding,
in this case the surrounding environment has a higher water potential than the
inside of the cell. As a result, the water from the surrounding environment will
move into the cell using osmosis. Water moves from an area of low concentration
to an area of high concentration causing the plant cell to swell.
2. The water on the inside of the plant, grass, will move outside of the grass to where
the salt is located, again the water is moving from low concentration to high
concentration. As a result, the grass would die because of the lack of water, dehydration,
inside of its cells.
Alana L, Toni M, Kaliah M, Autumn B
January 31, 2013
3. The function of the xylem in a plant is to transport water and other
minerals/nutrients up from the roots and to the rest of the plant. It is composed
various cells and it is a tube-like shape. As for the phloem of the plant, its
main function is to take food and other nutrients from the leaves down to the
rest of the plant; the phloem flows in the opposite direction, and sometimes
the same directions, as the xylem. However, when looking at the phloem of
the plant, it is slightly different than the plant’s xylem. The structure, or
appearance, of the plant’s phloem resembles a long, elongated, tube-like
structure.
4. If given a tree to plant, we would choose to plant the tree in the Winter month
as oppose to planting it in the summer. Planting trees in the winter gives the
plant’s roots a chance to settle during the cooler months, that way when the
spring and summer come it would be ready to grow and be better equip to
survive in the summer heat. The establishment of a good root system is
necessary in a plants life, especially for a tree that grows big and tall. Roots
not only supply water and nutrients from the soil, but it also helps to keep the
plant standing upright, that and the stem.