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A+ science fair research paper sure to impress the
The Effects of Different Light on Plants
Brady Whisenhunt
1729 SE East Drive
Bartlesville Mid High
4th hour
2-11-94
Abstract....................................................3
Introduction................................................5
Background..................................................6
Experiment..................................................8
Results.....................................................9
Conclusion.................................................11
Bibliography...............................................12
Abstract
I did my experiment to find the effects of different
shades of light on plants. Primarily I tried to find out
which shades work best for photosynthesis and growth. I also
wanted to find out which shades of the spectrum don't work
well with plants. I hypothesized that white light would work
the best because it contains all the colors of the spectrum.
I also hypothesized that red would work the next best,
followed by green and ultraviolet.
The materials I used were four plastic drop lights, four
60 watt light bulbs, four large cardboard boxes, eight clear
plastic cups, five inches of soil in each cup, eight pole
bean seeds, a tablespoon measurer, and eight 1 cm diameter
dowel rods. I planted each seed about 1 1/2 inches under the
surface of the soil in each cup and made drainage holes in
the bottoms of the cups. I installed the drop lights with a
white bulb, red and green party bulbs, and an ultraviolet
novelty bulb. I then put two plants and a light in each of
the cardboard boxes. I then monitored each plant over a four
week period of time, giving each 1 tablespoon of water every
other day. When a plant first came above the soil, I put a
dowel rod in for the plant to cling to.
The results of my experiment were very interesting. The
white light plants grew the best and looked the healthiest at
approximately 11.5 and 10 inches. The plants under the red
light grew to about 8 inches each, but didn't look as lush
and strong as the white plants. The green light plants
looked more healthy than the red plants but were only about 4
and 3.5 inches tall. The plants under the ultraviolet light
had barely enough visible light to survive. They didn't even
pop out of the soil until the third week, and grew only 0.6
and 1.4 inches tall.
According to my experiment, plants grow best in white
light. I believe this is true because the chlorophyll in the
leaves can filter out which color of light works best2. Even
though red light works very well with chlorophyll, white
light contains other colors of the spectrum such as violet
and blue which helps the plant greatly in photosynthesis3.
Background
Unlike many organisms, plants are autotrophic, meaning
they make their own food. They produce their food through a
process called photosynthesis. During this process, the
plant takes in light energy, oxygen, and water to form the
molecule glucose. A simple equation for photosynthesis is as
follows:
light energy
6O + H O C H O + 6O
chlorophyll
When light energy meets with chlorophll, electrons are
excited which starts photosynthesis. The wavelength, or
color, of the light depends on how much the chlorophyll will
absorb. For instance, chlorophyll a (C H O N Mg) and
chlorophyll b (C H O N Mg) absorb violet and red, but
reflect green light. As a result, plants with chlorophyll a
or b wouldn't grow well with green light. Since longer wave
ultraviolet light is almost on the invisible side of the
color spectrum, it probably wouldn't yield good results over
a short period of time, either. White light, however,
contains all of the colors of the spectrum. Therefore,
plants can filter out which colors they need to use for
photosynthesis from the white light. Since plants depend on
the right colors of light for photosynthesis, and they must
go through photosynthesis to eat, the color and quantity of
light depends on how tall and healthy a plant will be.
Since most complex life on earth is not autotrophic, we
must obtain our food from those organisms who are. The only
practical autotrophic food for us are green plants.
Therefore, photosynthesis is the most important biological
process on earth.
Experiment
For my experiment, I tested the effects of different
colors of light on plant growth. The materials I used were
four plastic drop lights, four 60 watt bulbs (different
colors), four large cardboard boxes, eight clear plastic
cups, five inches of soil in each cup, eight pole bean seeds,
a tablespoon measurer, and eight 1 centimeter diameter dowel
rods.
First, I poked holes in the bottom of the cups for
drainage. Next, I filled each of the cups 5 inches full of
moist soil and planted one seed in each cup 1 1/2 inches
under the surface of the soil. I then placed two cups each
to a different light. Next, I put each of the pairs cups six
inches apart from each other and twelve inches away from
their light and covered the pairs and lights with the
cardboard boxes. The colors of the light bulbs were white,
red, green, and ultraviolet. After each plant grew about an
inch out of the soil, I placed a dowel rod in the cup for
support. I gave the plants one tablespoon of water every
other day for a period of four weeks. I recorded the growth
of the plants once a week with an inch ruler.
Results
Every week I recorded my data with a ruler as the plants
grew. The plants under the white light grew the fastest.
The first week both of the plants were about an inch tall.
After the second week the plants were about two and a half
inches tall. When the third week came around, the plants
started going their separate ways; one measured 4.75 inches,
while the other measured almost six. At the beginning of the
fourth week, one plant was about 7.25 and the other measured
slightly over 8.5 inches. At the end of the experiment the
white light plants spurted to ten and 11.5 inches. At this
point the plants had six opposing leaves.
The pair in the red light, like the rest, stayed pretty
much consistently the same size at their measurements. At
the first week, the plants were just a little taller than the
white plants at a little more than an inch. They grew about
an inch each week for two weeks. At the fourth week, the
plants were about five inches. By the last measuring, the
plants grew three more inches. One plant had four large
leaves. The other had two large leaves and a pair of mid
sized leaves. These plants didn't look as healthy nd full as
the white ones. This could have possibly been due to too
many drainage holes.
The plants under the green light didn't come up to the
surface until the second week. By the third week, they were
an inch tall, and at the fourth week, the plants were exactly
two inches. At the end, the plants exhibited the same jump
in size; one plant was 3 1/2 inches tall. The other was
almost an even four. Both plants had but two small leaves
and neither was really even big enough to wrap around the
dowel rod, but they looked more healthy than the red plants.
The plants exposed to ultraviolet light were overall a
big disappointment. Neither even got to the surface of the
soil until about halfway between the third and fourth week.
At the end of the experiment, one plant was about a half an
inch and the other was a little over an inch tall. These
plants were much lighter in color than the others and only
had two tiny leaves.
Conclusions
I am very pleased with the results of this experiment.
Since pole beans grow relatively fast, I could get good
results in a short amount of time. As you can see on the
graph I made, the frequencies of the growth of the plants are
very related. The only real flaw I had with this project was
with the red plants' appearance, but as I have explained,
this was probably due to some sort of drainage problem.
Analyzing the graph, I can conclude with several facts.
The first is that white light works the best to help plants
grow and photosynthesize because it contains all the energy -
rich colors of the rainbow. A second conclusion is that red
light works fairly well because chlorophyll absorbs that
color well. A third conclusion is that green light works
poorly with plants because the chlorophyll in the leaves
reflects it. A fourth conclusion is that long wave
ultraviolet light is very bad in the exciting of chlorophyll
because it is almost at the invisible end of the spectrum. A
fifth and practical conclusion is that pole beans have a
relatively large spurt in growth after the fourth week of
planting. My final conclusion is that when trying to grow a
plant, it is best to use sunlight.
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