Grace Cussano
Purpose
To build an understanding of homeostasis by observing the ways in which plants
adapt to their
Environments respond to changes in their environments.
Guiding Question
How will the amount of moisture in a plant’s environment affect the number and
distribution of the
Stomata on one of its leaves?
Hypothesis
"e less moisture a plant has in its environment, the smaller the opening of its
stomata will be, and the
less stomata it will have per a given surface area, because it will be necessary for
plants in dryer areas to
prevent moisture from escaping where it is more scarce and thus valuable to the
organism.
Supplies
• Clear nail polish
• Elodea leaf (underwater)
• Fern leaf (terrestrial)
• Aloe leaf (desert)
• Small tweezers
• Microscope
• Slides
• slicy thing kn
• Camera
Proceduree
1. put nail polish on the bottom of the elodea, then let it dry.
2. Using the thin knife and tweezers, peel the nail polish off of the leaf.
3. Place the sliver of nail polish onto a slide, and focus it under the microscope.
4. Use the camera to document observations on each zoom level of the microscope.
5. Repeat steps 1-4 with the aloe leaf and the fern leaf.
Data
Our data was collected in a somewhat unorganized manner, mainly because of a
very speci#c issue with
what we were doing: in search of stomata, the respiratory cells of the leaves, we
were taking cells from the
top of the leaves where they are not present, rather than the underside where they
actually exist (this
change is now re$ected in our procedure). We also had some issues with the nail
polish distorting the
cells and a%racting numerous artifacts into the slides, as well as issues simply with
the availability of clear
nail polish throughout the several days during which we conducted our experiment.
Nonetheless, a&er
having examined countless samples under the microscope to li%le avail, we were
able to collect three
particularly signi#cant images which were very relevant in testing our hypothesis.
Displayed on the
following page, they are, in order from le& to right, the underside of an elodea
leaf, the underside of a leaf
belonging to a different terrestrial plant than the fern, but still one from a similar
environment, and the
George Woodliff-Stanley, David Hein, Morgan Benninger, and Sarah Knill
October 7 - October 24, 2010
Mr. Miller - Biology
Investigation #4 - Homeostasis Experiment
Dra" #1
underside of an aloe leaf. All three pictures were taken with the microscope at a
zoom level of 10x
magni#cation. "e differences in color between the desert sample and the other two
samples are directly
related to the fact that the desert sample was taken using the nail polish technique
while the other two
leaves were simply placed directly under the microscope, so they can be ignored.
Here are the images:
UNDERWATER
DESERT
Analysis and Discussion
TERRESTRIAL
Our hypothesis, on its own, was clearly supported by our data. We counted
approximately 60 stomata in
the picture of the terrestrial sample, which was taken at the same zoom level as the
desert plant, on which
we counted only 20. "e stomata on the terrestrial plant appeared to be slightly
larger than those on the
desert plant as well, further supporting our hypothesis. "e only area in which our
hypothesis was
incorrect was that of the underwater plant, which, despite having by far the most
wet environment, had
no stomata at all. Further research showed that this was because stomata are
respiratory pores whose
only functions are taking carbon dioxide from and releasing oxygen and moisture
back into the air, and
thus they cannot be found on leaves of plants which are submerged completely
underwater, where there
is no air from which carbon dioxide can be taken. Nonetheless, with regards only
to the plants whose
environments are not underwater, our hypothesis was supported, as the plant with
the more moist
environment had approximately three times as many stomata as the plant in the
drier environment.
Furthermore, the original fern leaf we tested (not pictured above due to the lack of
a photograph in
which the stomata are clearly visible) whose environment was also much more
moist than that of the
desert plant was host to what seemed like many more stomata than were on the
desert sample. If the
hypothesis were the only thing we cared about in this experiment, it would have
been a complete success.
"ere was a fundamental $aw, however, with our experiment as a whole.
"e purpose of our experiment, which has now been modi#ed to show what it used
to be and what it
should have been using struck-through text, was centered around the idea of how
plants adapt to their
environments, which is a key concept in the theory of evolution. It did not,
however, address the ways in
which plants actively respond to changes in their environments, which is what it
would have needed to
address to truly answer the question of what homeostasis is and how it works. Our
experiment was an
excellent example of evolution, in that the plants with the least amount of moisture
in their environments
George Woodliff-Stanley, David Hein, Morgan Benninger, and Sarah Knill
October 7 - October 24, 2010
Mr. Miller - Biology
Investigation #4 - Homeostasis Experiment
Dra" #1
presumably underwent a process of natural selection in which those with the
fewest and smallest stomata
were able to retain the most moisture and thus survive for the longest, leading to
higher reproduction
rates and dominance over time. Similarly, those in the moister environments did
not need to worry so
much about retaining water due to its abundance in their environments, and so
those with a greater
number of stomata which were able to process more carbon dioxide and oxygen
were more successful,
and thus became dominant over time in we%er areas. Clearly, our experiment was
more #t for our #nal
investigation in which we will be delving into the theory of evolution than it was
for this fourth
investigation, in which the intent was to learn about homeostasis. Nevertheless, we
did inadvertently
witness an example of homeostasis during the course of our experiment.
As we were observing one of the terrestrial leaves which we had pulled from its
plant and placed directly
under the microscope moments before, we noticed that the openings in the center
of its stomata were
slowly shrinking. "is was only something we observed only on the leaves which
were placed under the
microscope in their entirety, and not those from which we separated the surface
cells with clear nail
polish. Further research revealed that this was, indeed, a mechanism used by plants
to regulate the
amount of moisture exiting through the stomata. Once the leaf had been removed
from the plant, the
stomata closed in a #nal a%empt to preserve the moisture inside the leaf and keep
it alive.
In the end, this experiment was a positive learning experience, as it opened our
eyes to the small but
important difference between phenomena that are the result of evolution and those
which are truly
examples of homeostasis. It also gave us an opportunity to extend our knowledge
from investigation two,
in which we simply examined the structure and functionality of cells. We now
understand that the
number and distribution of stomata on the leaf of a plant differ between
environments with varying
amounts of moisture as a result of evolution, while the active changes in the size of
the stomata’s openings
in response to changes in the amount of moisture in the plants’ environments are
examples of homeostasis.
Furthermore, the additional research we did a&er completing our experiments
solidi#ed our
understanding of homeostasis as any mechanism in an organism which responds to
changes in its
environment to maintain equilibrium, or balance, between its internal conditions
and the external
conditions. For example, when a human is in a hot environment, they need to do
something to cool
themselves down, so that they can balance the heat around them with the coolness
inside of them, thus
maintaining equilibrium. "e body naturally takes care of this by sweating – the
moisture cools the body
down as it evaporates – a perfect example of homeostasis. In our experiment, when
we observed the
stomata openings shrinking, we were watching homeostasis in action, because the
cells were reacting to
having been disconnected from their moist environment, a%empting to achieve
equilibrium with their
new dry environment by retaining as much moisture as possible inside the leaf.