The effect of light intensity on the amount of chlorophyll in “Cicer arietinum”
The effect of light intensity on the amount of chlorophyll in “Cicer arietinum”
Extended Essay
Biology (SL)
“The effect of light intensity on the amount of chlorophyll in “Cicer
arietinum”
Word count: 4 413 words
Content
Abstract ……………………………………………………………………………… 2
Introduction ………………………………………………………………………….. 3
Hypothesis …………………………………………………………………………… 3
Method:
Description ..………………………………………………………………………….. 8
Results ……………………………………………………………………………….. 10
Discussion ……………………………………………………………………..…….. 14
Conclusion ………………………………………………………………………..….. 14
Evaluation of the method ………………………………………………………..…… 15
Bibliography …………………………………………………………………………. 16
Abstract.
Plants, growing on the shaded area has less concentrated green color
and are much longer and thinner than plants growing on the sun areas as
they are dark green, short and thick. Research question was: “How does the
amount of chlorophyll-a and chlorophyll-b, gram per gram of plant, depends
on the light intensity in which plants are placed?”
Hypothesis suggests that there are several inner and outer factors
that affect the amount of chlorophylls a and b in plants and that with the
increase of light intensity the amount of chlorophyll will also increase
until light intensity exceeds the value when the amount of destructed
chlorophylls is greater than formatted thus decreasing the total amount of
chlorophylls in a plant.
The seeds of Cicer arietinum were divided into seven groups and
placed into various places with different values of light intensities.
Light intensities were measured with digital colorimeter. After three weeks
length was measured. Then plants were cut and quickly dried. Their biomass
was also measured. Three plants from each group were grinded and the
ethanol extract of pigments was prepared. The amount of chlorophylls was
measured using method of titration and different formulas.
The investigation showed that plants growing on the lowest light
intensity equal 0 lux contained no chlorophyll and had the longest length.
The amount of chlorophyll quickly increased and length decreased with the
increase of light intensity from 0 lux to 1200 lux. The amount of
chlorophyll in plants unpredictably decreased during light intensity equal
to 142 lux and than continued increasing and didn’t start decreasing
reaching very high value (1200 lux).
The sudden decrease happened due to mighty existence of some inner
genetical damages of seeds which prevented them from normal chlorophyll
synthesis and predicted decrease didn’t decrease because extremely high
light intensity was not exceeded.
Word count: 300 words
I. Introduction.
This theme seemed to be attractive for me because I could see that
results of my investigation could find application in real life.
While walking in the forest in summer I saw lots of plants of
different shades of green color: some of them were dark green, some were
light green and some even very-very light green with yellow shades, hence I
became very interested in this situation and wanted to know why it happens
to be so. I also saw that those plants that were growing on sunny parts of
forest, where trees were not very high, had dark green color and those,
that were growing in shady parts of the same forest had very light green
color. They also had difference in their length and thickness – those, that
were growing on light were very short, but thick and strong, and those,
growing in shady regions were very thin and fragile.
Hence I became very interested in finding scientifical description of
my observations.
The aim of my project is to find out how does the changes in light
intensity affect balance of chlorophyll in Cicer arietinum.
II. Hypothesis.
There are several factors that affect the development of chlorophyll
in plants.[1]
Inner factors. The most important one is – genetical potential of a
plant, because sometimes happen mutations that follow in inability of
chlorophyll formation. But most of the times it happens that the process of
chlorophyll synthesis is broken only partly, revealing in absence of
chlorophyll only in several parts of the plant or in general low rate of
chlorophyll. Therefore plants obtain yellowish color. Lots of genes
participate in the process of chlorophyll synthesis, therefore different
anomalies are widely represented. Development of chloroplasts depends on
nuclear and plastid DNA and also on cytoplasmatic and chloroplastic
ribosomes.
Full provision of carbohydrates seem to be essential for chlorophyll
formation, and those plants that suffer from deficit of soluble
carbohydrates may not become green even if all other conditions are
perfect. Such leaves, placed into sugar solution normally start to form
chlorophyll. Very often it happens that different viruses prevent
chlorophyll formation, causing yellow color of leaves.
Outside factors. The most important outside factors, affecting the
formation of chlorophyll are: light intensity, temperature, pH of soil,
provision of minerals, water and oxygen. Synthesis of chlorophyll is very
sensitive to all the factors, disturbing metabolic processes in plants.
Light. Light is very important for the chlorophyll formation, though some
plants are able to produce chlorophyll in absolute darkness. Relatively low
light intensity is rather effective for initialization and speeding of
chlorophyll development. Green plants grown in darkness have yellow color
and contain protochlorophyll – predecessor of chlorophyll а, which needs
lite to restore until chlorophyll а. Very high light intensity causes the
destruction of chlorophyll. Hence chlorophyll is synthesized and destructed
both at the same time. In the condition of very high light intensity
balance is set during lower chlorophyll concentration, than in condition of
low light intensity.
Temperature. Chlorophyll synthesis seems to happen during rather broad
temperature intervals. Lots of plants of умеренной зоны synthesize
chlorophyll from very low temperatures till very high temperatures in the
mid of the summer. Many pine trees loose some chlorophyll during winters
and therefore loose some of their green color. It may happen because the
destruction of chlorophyll exceeds its formation during very low
temperatures.
Provision with minerals. One of the most common reason for shortage of
chlorophyll is absence of some important chemical elements. Shortage of
nitrogen is the most common reason for lack of chlorophyll in old leaves.
Another one is shortage of ferrum, mostly in young leaves and plants. And
ferrum is important element for chlorophyll synthesis. And magnesium is a
component of chlorophyll therefore its shortage causes lack of production
of chlorophyll.
Water. Relatively low water stress lowers speed of chlorophyll synthesis
and high dehydration of plants tissues not only disturbs synthesis of
chlorophyll, but even causes destruction of already existing molecules.
Oxygen. With the absence of oxygen plants do not produce
chlorophyll even on high light intensity. This shows that aerobic
respiration is essential for chlorophyll synthesis.
Chlorophyll.[2] The synthesis of chlorophyll is induced by light.
With light, a gene can be transcripted and translated in a protein.
The plants are naturally blocked in the conversion of protochlorophyllide
to chlorophyllide. In normal plants these results in accumulation of a
small amount of protochlorophyllide which is attached to holochrome
protein. In vivo at least two types of protochlorophyllide holochrome are
present. One, absorbing maximally at approximately 650 nm, is immediately
convertible to chlorophyllide on exposure to light. If ALA is given to
plant tissue in the dark, it feeds through all the way to
protochlorophyllide, but no further. This is because POR, the enzyme that
converts protochlorophyllide to chlorophyllide, needs light to carry out
its reaction. POR is a very actively researched enzyme worldwide and a lot
is known about the chemistry and molecular biology of its operation and
regulation. Much less is known about how POR works in natural leaf
development.
ALA Portoporphyrine
