![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgKfJyKWNPiybra4dev_U5YTR41Nt_xQrZiqWraN9qivGfnLpjPcFGO6y6KbhLzj_J0AnwAINoUVNhxldkPIFAGG13iC3_XOKTrsIRnF5hjeFS1SqUEyy5kIJLb9LQEXijiGwK0JKqgJe0N/s200/test_tube_stand_0109.jpg)
·
4
test tubes with rubber stoppers
·
A
rack to hold the 4 test tubes
·
Elodea
plants
·
Distilled
Water
·
Phenol
Red
·
Bromothymol
Blue
·
Light
Source
·
Stirring
Rod
To
begin, each of the four test tubes must be rinsed with distilled water and then
filled three-fourths full with distilled water. Using chemical resistant gloves
and under adult supervision, carefully put 5 drops of phenol red and 5 drops of
bromothymol blue in each test tube. Carefully mix the chemical indicators in
the test tube by moving it in an upward and downward motion. Once the chemicals
are completely mixed, place equal length sprigs of the Elodea plant in 3
of the containers then seal all four test tubes. Once the test tubes are
sealed, remove the chemical resistant gloves and turn them inside out without
letting the outer part of the glove touch the skin. Dispose of the gloves in a
container marked with “Hazardous Material” for safety.
Lightly cover one test
tube with an Elodea plant using tissue paper to simulate shade, put an
uncovered Elodea plant in total darkness, and one test tube with an Elodea
plant and the empty test tube with receive full light. Place the “shaded” test
tube, the empty test tube, and the Elodea assigned to full sunlight in the test
tube rack. Place the rack with the three test tubes in exposure to the provided
light source. Leave the test tubes undisturbed in their assigned lighting until
there is a noticeable change in color in the surrounding liquid. In my personal
experiment, we waited 48 hours to reevaluate our plants. When a color change
has occurred, remove the tissue paper from the shaded plant and return it as
well as the plant subjected to darkness to the test tube rack for comparison. The
color scale is a spectrum with yellows being the most acidic and blues and
purples being the most basic. It is important to note that oxygen is basic and
carbon dioxide is acidic. This means that any containers shaded yellow will
have a higher level of carbon dioxide and any containers shaded purple will
have a higher oxygen level. For example, humans exhale carbon dioxide so if someone
was to blow into the same concentration that the plants are exposed to, the
liquid would turn yellow.
The
results should depict that the full sun and empty test tube containers should
remain purple, while the shaded plant is a lighter purple to dark pink color.
The plant exposed to complete darkness should have more of a yellow color. This
is due to the fact that the plants exposed to full sun should be respiring more
oxygen into the surrounding liquid due to its proximity to light as demonstrated
in the previous experiment while the plant in darkness should not be respiring
much to conserve energy with the shaded plant landing somewhere in the
mid-range. My experiment is an anomaly as listed left to right are the full sun,
shaded, empty, then total darkness test tubes (shown below). Although the plant that was
exposed to full sun is the healthiest looking, it should be in a purple colored
liquid rather than bright yellow. The Elodea plant that was exposed to total
darkness began to lose its green color and began to wilt which promotes the
necessity of a light source for even aquatic plants. If plants are exposed to
the proper conditions for efficiency, they should be respiring at a faster rate
which would turn the concentration blue. This indicates that if a plant was to
respire and carry out photosynthesis at the same rate it should be surrounded
by a red or amber concentration. This situation would most likely happen around
dawn and dusk because the plant would not be exposed to full sunlight as it
would during midmorning, lunchtime, or afternoon when the rate of
photosynthesis is at its highest. Similarly, there is no natural light source
during night so no photosynthesis would be occurring and the rate of
respiration would be at its highest.