Conclusion:
I conclude that the growth media have had independent effects on the growth of the plants. As only one seed germinated under the green film and the rest did not show any signs of germination, this leads me to conclude that the filter paper was not suitable for the growth of cress for the experiment as well, as if it was germination would have taken place in at least the majority of seeds. The Perlite made it difficult to measure the height of the cress seeds and a few seeds did not germinate in the Perlite either, which indicates that Perlite is not a suitable growth medium for this study.
Actual Study data:
The actual study has been designed to test how different wavelengths of light will affect the photosynthetic rate of plants and this will be measured by the heights the cress reach. There are two types of chlorophyll found in plants, Chlorophyll a and b. The difference between the two is that they absorb light at the same wavelengths, in varying quanta. Chlorophyll a absorbs blue and red light in roughly the same quantity. Chlorophyll b however absorbs blue light very effectively and red light at roughly 25% less intensity [than type a]. Depending on the type of chlorophyll present, the final height of the plants should differ accordingly
Method:
The containers had black card attached around the side to block out any other light that could enter other than the filtered light coming through the films. The films were then placed on the ring of card surrounding the trays. Ten seeds were planted per tray and each container had cotton wool as the growth medium. Three different films were used red, green and blue. Next the seeds were watered. Afterwards the containers were placed by a window. The plants were measured daily and watered/fed daily as necessary. The plants were also moved out of direct sunlight during measurement to ensure reliability and accuracy.
Null hypothesis:
The different wavelengths of light the plants receive will not affect their photosynthetic rate and so their final heights in respect to the various wavelengths of light applied will not be distinct.
Experimental Hypothesis:
The different wavelengths of light the plants receive will affect the plants photosynthetic rate and so indirectly affect the plants final height. I also hypothesise that the plants under red and blue light will grow to greater average heights.
Results:
Analysis:
This graph shows that the pigments found in the cress leaves [mainly chlorophyll a] absorb blue and red range wavelengths. This is supported by the higher (average) heights for the blue and red filmed cress. The plants subjected to green light were hindered by the light, as the mean height for the green film plants is less than that of the red and blue plants by a significant amount. Using the data collected, I can say that the main pigment found in cress leaves is chlorophyll a. This is because the plants show increased height under blue and red light and have roughly the same average maximum heights. This is due to chlorophyll a absorbing photons of red and blue light readily compared to other photons/wavelengths. This in turn results in an increased photosynthetic rate [under red and blue light], which leads to taller cress. The blue light was absorbed in slightly lower amounts; hence the slightly smaller average final height.
The experiment all things considered produced good results. It was not clear cut at first but after carefully looking at the various wavelength ranges and the absorption spectra of chlorophyll a/b, the results became understandable. The specific energies that the electrons can be liberated by are exact. For similar future experiments I would recommend recording the light intensity coming through each of the films and using E=h x f, to determine the exact wavelengths of light coming through the coloured films. This way the precise wavelengths of light coming through the films can be obtained and thus improve the solidarity of the method.
Statistical analysis:
I have chosen to use the ANOVA statistical test, as it is the only test that measures more than two sets of data that consist of numerical values. This test will test for a difference between each of the sets. Essentially the test will allow me to find any trends and patterns.
The value that determines whether or not my null hypothesis is true is the P-Value. This value is the probability that the null hypothesis is true [that is to say that there is no difference between the data sets (red, green and blue), which also means that the varied wavelengths of light do not have any effect on the cress plants growth, and so do not affect their final heights]. The test has calculated a probability of ≈0.39%. If the probability is >5% then there is no significance between the data sets, however if the value is <5% then there is a significant difference in the data somewhere. As can be seen the probability obtained is very small for the null hypothesis and so clearly there is a distinct difference between the data sets.
The variance values allow one to discover what is affecting the P-Value. The variance in this case is larger within the group than between the groups, as it should be in this case as the plants heights should vary. This is due to intraspecific gene variations and small complex environmental and genetic variables that influence the cress plants growth. Even though the variance between each of the sets is large it is shown that the different wavelengths of light do clearly have an effect on the plants growth, and as a result on the plants final heights, as the difference between the three variance values is extremely large.
Averages (final heights):
Mean:
Red – 46.6mm
Blue – 45.8mm
Green – 40.2mm
Median:
Red film – 53.5mm
Blue – 45mm
Green – 43.5mm
These average final heights also lend support to my hypothesis. The Blue light clearly benefitted the plant and so it grew to a greater final height due to an increased level of photosynthesis. The red film also experienced the same factors and came out with the second greatest final height. Red light ideally should have procured the greatest average as it is absorbed in slightly higher quanta. The chlorophyll absorption graph shows that chlorophyll a absorbs blue light at wavelength ranges 400-450nm and red light at 645-670nm. Using these ranges it may be possible that the light passing through the blue film was slightly out of the range of the absorption spectrum, this may have lead to the slightly decreased average of the blue film cress compared to the red film cress.
The medians calculated show that the cress that grew under red light had the majority greater heights. This is essentially showing that the red light influenced the cress growth more than the green or blue light. The blue light also influenced the plants growth positively but not to as greater extent as the red light.
Bibliography:
Websites:
ANOVA - http://www.physics.csbsju.edu/stats/anova.html [statistics test]
Test Advice - http://www.med.umkc.edu/tlwbiostats/choosetest.html [statistics tests]
Image - http://www.daviddarling.info/images/ [chloroplast watermark]
Biological/Physical principles - http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html [photosynthesis/photoelectric effect]
Biological principle - http://dwb.unl.edu/Teacher/NSF/C11/C11Links/gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookPS.html [photosynthesis/photoelectric effect]
Physical information -
http://en.wikipedia.org/wiki/Electromagnetic_spectrum
Biological information -
http://en.wikipedia.org/wiki/Chlorophyl [chlorophyll a/b]
Germination -
http://plantphys.info/seedg/seed.html
Books:
Salter’s Nuffield Advanced Biology, [electron behaviour in plants]
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