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   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

Страницы: 1, 2, 3


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