The effect of light intensity on the amount of chlorophyll in “Cicer arietinum”
color. It can be proposed that olive-green color is obtained because grey
phaeophetyn is mixed with other plant pigments.
So titration is one of the visual methods that can be used in order to
find the mass of chlorophyll in plants.
All the measurements and even chromatography were done three times and
the mean value was taken, for chromatography grey color was confirmed.
Table 1. Plant pigments.
|Name of the pigment |Color of the pigment |
|Chlorophylls ( a and b ) |Green |
|Carotene |Orange |
|Xanitophyll |Yellow |
|Phaeophytin-a |OLIVE BROUN or GREY |
IV. Results.
Table 2. Raw data.
|Number of |Light intensity (lux) |
|plant | |
|0 |0,273 |0,041 |84,98 |41,89 |0,0000 |
|20,5 |0,579 |0,056 |90,33 |41,76 |0,0496 |
|27,5 |0,332 |0,033 |90,06 |36,33 |0,1462 |
|89,5 |0,181 |0,018 |90,06 |19,81 |0,1769 |
|142 |0,511 |0,047 |90,80 |41,33 |0,0697 |
|680 |0,338 |0,043 |87,28 |29,33 |0,1557 |
|1220 |0,301 |0,034 |88,70 |18,64 |0,1939 |
[pic]
Calculation of amount of chlorophyll in plants basing on the results of
titration
H2 SO4 + C56 O5 N4 Mg => C56 O5 N4 H + MgSO4
Concentration of H2SO4 is 0,01 M
C – concentration
V – volume
n – quantity of substancy
m – mass
Mr – molar mass
For light intensity equal to 20,5 lux.
n = V (in dm3) ? C
2 ? 10-3 ? 0,01 = 2 ? 10-5
n = m / Mr => m = n ? Mr
m = 2 ? 10-5 ? 832 = 1,664 ? 10-2 grams
mass of plant mass of chlorophyll
1,68 grams - 0,08335 grams of
chlorophyll
1 gram - x grams of
chlorophyll
Hence there are 0,0496 grams of chlorophyll.
[pic]
Table 5. The correlation between mean length of plants and mean dry
biomass.
| | | | | | | |
| | | | | | | |
[pic]
Table 6. The correlation between mean length and mass of chlorophyll per 1
g of plant.
Site |Mean length, cm |Rank (R1) |Mass of chl. In 1 g |Rank (R2) |D (R1-
R2) |D^2 | |1 |41,89 |1 |0,0000 |7 |-6 |36 | |2 |41,76 |2 |0,0496 |6 |-4
|16 | |3 |36,33 |4 |0,1462 |4 |0 |0 | |4 |19,81 |6 |0,1769 |2 |4 |16 | |5
|41,33 |3 |0,0697 |5 |-2 |4 | |6 |29,33 |5 |0,1557 |3 |2 |4 | |7 |18,64 |7
|0,1939 |1 |6 |36 | | | | | | | | | |
Rs = -1
| | | | | | | | | | | | | | | |
[pic]
Table 7. The correlation between mean dry biomass and mass of chlorophyll
per 1 g of plant.
Site |Mean dry biomass, g |Rank (R1) |Mass of chl. In 1 g |Rank (R2) |D
(R1-R2) |D^2 | |1 |0,041 |4 |0,0000 |7 |-3 |9 | |2 |0,056 |1 |0,0496 |6 |-5
|25 | |3 |0,033 |6 |0,1462 |4 |2 |4 | |4 |0,018 |7 |0,1769 |2 |5 |25 | |5
|0,047 |2 |0,0697 |5 |-3 |9 | |6 |0,043 |3 |0,1557 |3 |0 |0 | |7 |0,034 |5
|0,1939 |1 |4 |16 | | | | | | | | | | | | | | | | | |Rs = -0,57 | | | | | |
| |
| | | | | | | | | | | | | | | | | | | | | | | |
[pic]
V. Discussion.
Several tendencies can be clearly seen.
For the first, with the increase of light intensity mean length of
plants is decreasing, but there are exceptions. For light intensity 142 lux
the value of mean length is approximately equal to the values of length for
light intensities 0 lux and 20,5 lux. If exclude this data it is also seen
that for light intensity equal to 680 lux mean length is also slightly
falling out from the main tendency – decreasing from 19.81 cm.
The second tendency is increase of mass of chlorophyll per 1 gram of
plant biomass with the increase of light intensity. But the values of mass
of chlorophyll of those plants under light intensities 142 lux and 680 lux
are falling out from the main tendency. The first and the second ones are
too small – approximately equal to the value corresponding to 20.5 lux
light intensity and to 89.5 lux respectively. This may happen because not
all the seeds of Cicer arietnum were of the same quality, because it is
impossible to guarantee that more than 250 seeds in one box have the same
high quality. At the mean time it was expected that starting from the light
intensity more than 680 lux the amount of chlorophyll in plants will
decrease, because the value of destructed chlorophyll with be bigger than
the value of newly formatted. But the experiments showed that the amount of
chlorophyll was constantly increasing even when the light intensity level
exceeded the point 1220 lux. This could happen because light intensity
equal to 1220 lux is not so extremely high that the amount of total
chlorophyll in plants will start decreasing.
Also it is clearly seen that there are no correlations between light
intensity and values of wet and dry biomass.
Basing on these arguments the sudden decrease of the amount of
chlorophyll in plants placed on light intensity equal to 142 lux was likely
to be insignificant and could not be considered as a trend.
But it is impossible to forget such important factor as plant hormones
that affect the growth and development of plants. There are five generally
accepted types of hormones that influence plant growth and development.
They are: auxin, cytokinin, gibberellins, abscic acid, and ethylene. It is
not one hormone that directly influences by sheer quantity. The balance and
ratios of hormones present is what helps to influence plant reactions. The
hormonal balance possibly regulates enzymatic reactions in the plant by
amplifying them.
VI. Conclusion.
Due to results of my investigation it is seen that my hypothesis
didn’t confirm fully (for example, comparing the diagram 1 and diagram 7),
because I proposed that when light intensities will be very high, mass of
chlorophyll in plant will start decreasing and due to my observations it
didn’t happen. I should say that the only reason I can suggest is that I
haven’t investigated such extremely high light intensities, so that
chlorophyll start destructing. But if we will not pay attention to that
fact the other part of my hypothesis was confirmed and mass of chlorophyll
in plants increased with the increase of light intensity. Furthermore I
didn’t estimate amount of plant hormones and so didn’t estimate their
influence on results.
Questions for further investigation:
1. Investigating very high light intensities.
2. Implementation of colorimetric analysis.
3. Paying attention to estimation of plant hormones level.
Those questions should be further investigated in order to get clearer
picture and more accurate results of the dependence of the amount of
chlorophyll in plants on the light intensity, knowing the fact that the
amount of chlorophyll has a tendency to decrease at extremely high light
intensities. So this statement needs an experimental confirmation and as in
this investigation conditions with extremely light intensity were not
created in further investigations they have to be created.
Implementation of colorimetric analysis is also very important thing,
because it gives much more accurate results comparing with the titration
method. The colorimetric method suggests that as different pigments absorb
different parts of light spectrum differently, the absorbance of a pigments
mixture is a sum of individual absorption spectra. Therefore the quantity
of each individual pigment in a mixture can be calculated using absorbance
of the certain colors and molecular coefficients of each pigment. This was
proposed by D. A. Sims, and J. A. Gamon (California State University,
USA)[5] with the reference on Lichtenthaler (1987).
VII. Evaluation.
There are several results in my work, that are falling out from the
main tendencies. It may seem that such results may occur due to different
percentage of water in plants, but when I was calculating mass of
chlorophyll in 1 gram of plant I was using only values of mean dry biomass
so it couldn’t affect my results. (see table 3)
At the same time such differences in the percentage of water are
easily explained. The rate of evaporation of water from plants, which were
put under 1220 lux light intensity was much higher than of those put under
20.5 lux light intensity, therefore percentage of water in the soil may
vary, though I provided all the plants with the same volume of water at the
same periods of time.
One more reason that could be proposed is the reason connected with
the pH of water with which flowers were provided. It was not measured but
the thing that could have happened is that it had somehow changed the pH of
soil in which seeds were placed and therefore changed the amount of
synthesized chlorophyll.
Titration is not a perfect way of obtaining results. This happens
because the method is based on visual abilities of a person – he has to
decide whether the color he obtained is dark olive-green or not so dark
olive-green. Such a situation concerns lots of mistakes due to different
optical abilities of each person, even some humans are not able to
distinguish those colors, because of the disease called Daltonism.
Even those who do not suffer from this disease can also make mistakes
in such experiment. It is known that people who suffer from Myopia can
hardly see objects that are far from them, but don’t have problems with
objects that are near, but it is also important to take into consideration
the fact that their ability to distinguish colors is also lower comparing
with humans with normal eyesight.
There also exist the so called human factor, which also affects the
investigation. Man can’t be absolutely objective, because sometimes it is
too hard for a person to falsify his own theory or hypothesis, so one can
ignore results that are not suitable for his statements and select only
those that are suitable, which will also affect the investigation not in
good way.
So as human’s eye is not a perfect instrument and humans are not
perfectly objective there should be other methods of investigating the
amount of chlorophyll in plant.
Moreover titration method doesn’t distinguish between chlorophylls-a
and chlorophyll-b, phaeophytin-a and phaeophytin-b, as their colors differ,
this giving not very accurate results. Also due to this limiting factor it
is impossible to know whether the whole amount of chlorophyll reacted with
the sulfuric acid and again it adds an uncertainty to the results.
Furthermore the saturation of color depends on the extent of dilution and
it is nearly impossible to say if the solution was diluted till the same
color or not, because it is very difficult to distinguish between different
shades of olive green color.
BIBLIOGRAPHY
1) Allott, Biology for IB diploma (standard and higher level), Oxford
University Press, ISBN 0-19914818
2) M. Roberts, M. Reisse, G. Monger, Biology: principles and approaches,
Nelson, ISBN 0-17-44-8176-4
3) T. King, M. Reiss, M. Roberts, Practical advanced biology, Nelson
Thorns, ISBN 0-170448308-
4) Викторов Д. П., Практикум по физиологии растений. – 2-е изд.
– Воронеж: ВГУ, 1991
5) http://www.ac-creteil.fr/svt/Tp/Tp2/Tp2UK2/fiches_them_choix-
P2/genechloro.doc, 15/03/2004
6) http://vcsars.calstatela.edu/esa_posters/ds/dan_esa99.html 05/05/2004
7) http://www.agsci.ubc.ca/courses/fnh/410/colour/3_21.htm, 16/03/2004
8) http://vcsars.calstatela.edu/esa_posters/ds/dan_esa99.html, 22/02/2004
9) http://www.charlies-web.com/specialtopics/anthocyanin.html. 17/04/2004
10) http://www.ch.ic.ac.uk/local/projects/steer/chloro.htm, 11/04/2004
11) http://www.bonsai.ru/dendro/physiology5.html 02/04/2004
12) http://www.iger.bbsrc.ac.uk/Publications/Innovations/in97/Ch2.pdf,
06/05/2004
-----------------------
[1] http://www.bonsai.ru/dendro/physiology5.html 02/04/2004
[2] www.iger.bbsrc.ac.uk/igdev/iger_innovations/ 06/05/2004
[3] http://www.ch.ic.ac.uk/local/projects/steer/chloro.htm 11/04/2004
[4] 8:B>@>2 . ., @0:B8:C< ?> D878>;>388 Викторов Д. П., Практикум по
физиологии растений. – 2-е изд. – Воронеж: ВГУ, 1991, p.66
[5] http://vcsars.calstatela.edu/esa_posters/ds/dan_esa99.html 05/05/2004
-----------------------
Chlorophyll, gram per gram of plant.
Light intensity, lux
Diagram 1. The predicted change of amount of chlorophyll in leaves of
depending on light intensity
0,57<0,79, therefore there is no significant correlation between mean
length of plants and mean dry biomass.
POR
max
plateau
There is negative correlation between mean length of plants and mass of
chlorophyll per 1 g of plant
0,57<0,79, therefore there is no significant correlation between mean dry
biomass and mass of chlorophyll per МD[pic]НD[pic]1 g of plant
