The Study of Chlorophyll Content in Various Plants

THE STUDY OF CHLOROPHYLL CONTENT IN VARIOUS PLANTS A Project Report

Submitted by

ABHISHEK MATH

In partial fulfillment of the

CBSE GRADE XII IN BIOLOGY AT

AECS MAGNOLIA MAARUTI PUBLIC SCHOOL Arakeri, off Bannerghatta Road, Bangalore- 560076

2014-15

CERTIFICATE

This is to certify that Abhishek Math of grade XII, AECS MAGNOLIA MAARUTI PUBLIC SCHOOL, BANGALORE with register number _______________________ has satisfactorily completed the project in Biology on STUDY OF CHLOROPHYLL CONTENT IN VARIOUS PLANTS, in partial fulfillment of the requirements as prescribed by CBSE in the year 2014-2015.

Signature of the Candidate

Signature of Teacher in Charge

Signature of the Principal Signature of the ExternalExaminer

ACKNOWLEDGEMENT

I warmly acknowledge the continuous encouragement and timely suggestions offered by our dear principal Dr. SeemaGoel. I extend my hearty thanks for giving me the opportunity to make use of the facilities available in the campus to carry out the project successfully

I am highly indebted to Mrs. Nikhila and Mrs. Gayathri for the constant supervision, providing necessary information and support in completing the project. I would like to express my gratitude towards them for their kind co-operation and encouragement.

Finally, I extend my gratitude to one and all who are directly or indirectly involved in the successful completion of this project work.

Signature of the Candidate

TABLE OF CONTENTS

S no

Topic

Page number

1

Introduction

1

2

Objective

4

3

Scope and limitations

5

4

Theory

6

5

Experiment

11

6

Procedure

13

7

Observations

17

8

Result

18

9

Bibliography

19

INTRODUCTION Chlorophyll is a green photosynthetic pigment found in chloroplasts of organisms like cyanobacteria, algae and plants. Its name is derived from the Greek words chloros, meaning „green‟ and phyllon meaning „leaf‟. First isolated by Joseph BienaimeCaventou and Pierre Joseph Pelletier in 1817, chlorophyll is an extremely important biomolecule, playing a vital role in nature. Chlorophyll is critical in photosynthesis, where the green pigment plays the role of absorbing energy for plants to use. There are at least seven types of chlorophyll known as chlorophyll a, b, c, d, e, bacteriochlorophyll and bacterioviridin. Chlorophyll absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. However, it is a poor absorber of green and near green portions of spectrum, hence green colour of chlorophyllcontaining tissues. Chlorophyll molecules are specifically arranged in and around photosystems that are embedded in thylakoid membranes of chloroplasts. In these complexes, the vast majority of chlorophyll serves two primary functions : to absorb light, and to transfer that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction centre of the photosystems. The two currently accepted photosystem units are photosystem II and photosystem I, which have their own distinct reaction centre chlorophylls, named P680 and P700, respectively. These pigments are named after the wavelength ( innanometres ) of their red peak absorption maximum. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct, and determined by each other and

the protein structure surroundingthem. Once extracted from the protein into a solvent (like acetone or methanol ), these chlorophyll pigments can be separated in simple paper chromatography experiment and, based on the number of polar groups between chlorophyll a and chlorophyll b, will separate out on the paper. The function of reaction centre chlorophyll is to use the energy absorbed by, and transferred to it from other chlorophyll pigments in the photosystems, so that the reaction centre undergoes a charge separation, a specific redox reaction in which the chlorophyll donates an electron into a series of molecular intermediates called an electron transport chain. The charged reaction centre chlorophyll (P680+) is then reduced back to its ground state by accepting an electron. In photosystem II, the electron that reduces P680+ ultimately comes from the oxidation of water into O2 and H+ through several intermediates. This reaction is how photosynthetic organisms such as plants produce O2 gas, and is the source for practically all the O2 in earth‟s atmosphere. Photosystem I typically works in series with photosystem II; thus the P700+ of photosystem I is usually reduced via many intermediates in the transfer reactions in the thylakoid membrane by electros ultimately from photosystem II. Electron transfer reactions in the thylakoid membranes are complex, however, the source of electron used to reduce P700+ can vary. The electron flow produced by the reaction centre chlorophyll pigments is used to shuttle H+ ions across the thylakoid membrane, setting up a chemiosmotic potential used mainly to produce ATP chemical energy; and those electrons reduce NADP+ to NADPH, a universal reductant used to reduce CO2 into sugars as well as for other biosynthetic reductions.

Reaction centre chlorophyll – protein complexes are capable of directly absorbing light and performing charge separation events without other chlorophyll pigments, but the absorption cross section ( the likelihood of absorbing a photon under a given light intensity) is small. Thus, the remaining chlorophylls in the photosystem and antenna pigment protein complexes associated with the photosystems all cooperatively absorb and funnel light energy to the reaction centre. Besides chlorophyll a, there are other pigments called accessory pigments, which occur in these pigmentprotein antenna complexes. Chlorophyll is a chlorine pigment, which is structurally similar to and produced through the same metabolic pathway as other porphyrion pigments such as heme. At the centre of the chlorine ring id=s a magnesium ion. At time of discovery in 1900s, this was the first time this element was detected in a living tissue. the chlorine ring can have several different side chains, usually including a long phytol chain. There are a few different forms that occur naturally but most widely distributed form in terrestrial plants is chlorophyll A. after initial work done by german chemist Richard Willstatter spanning from 1905-1915, general structure of chlorophyll a was elucidated by Hans Fischer in 1940. By 1960, when most of stereochemistry of chlorophyll a was known, Robert published a total synthesis of the molecule. In 1967, Ian Fleming completed the last remaining stereo chemical elucidation, and in 1990 Woodward and coauthors published an updated synthesis.

OBJECTIVE

The objective of this experiment is to study the chlorophyll levels in different plant species. In this experiment I seek to use chromatography to separate the various pigments present in the leaves of various plants. Through this, we can measure the amount of each pigment present in each type of leaf and hence, understand the chlorophyll content in the assorted plants. We extract the pigments from various leaves, and with the addition of various chemicals methodically, we separate the various pigments present in leaves like, chlorophyll a, chlorophyll b, carotenioids, and xanthophylls. We then measure the quantity of each, and put all the data in a table to compare the levels of various pigments in various plants. In this manner, we also perform an internal study where we compare pigment levels in yellow and green leaves of the same plants to understand the pigment difference when senescence takes place and leaf yellowing takes place.

SCOPE AND LIMITATIONS This project also helps us in understanding the importance of chlorophyll for animals as well as in human diet. Chlorophyll is known to be the plant‟s “blood”, in other words the principle physiology of plant life. Chlorophyll is so important to plants because it performs metabolic functions such as respiration and growth. Just as significantly, chlorophyll supplies our bodies with the much needed, micronutrient magnesium which is essential to how our body produces energy. Many health specialists use chlorophyll as a tonic for the blood due to its richness in nutrients.

THEORY Chlorophyll is a green pigment found in cyanobacteria and chloroplasts of algae and plants. It is a critical biomolecule in the process of photosynthesis, which allows plants to absorb energy from light. It is present in the chloroplast‟s thylakoid membrane. Within the chloroplast, there is a membranous system of grana, stroma lamellae and fluid stroma. The membrane system is responsible for trapping light energy and for synthesis of ATP and NADPH.

The colour of leaves we see is not due to a single pigment but due to four pigments namely chlorophyll a, chlorophyll b, xanthophylls and carotene.

Although Chlorophyll a is the chief pigment associated with photosynthesis, other thylakoid pigments like chlorophyll b, xanthophylls and carotenes are the accessory pigments. They absorb light and transfer the energy to chlorophyll a.

The function of the vast majority of chlorophyll is to absorb light and transfer that light energy to a specific chlorophyll pair in the reaction centre of the photosystems.

There are two photosystem unit present photosystem I (PS I) and photosystem II (PS II) that have their own reaction centers P700 and P680 respectively. Within each PS I and PS II their are photochemical light harvesting systems present which are made up of many pigment molecules bounded to proteins.

Chlorophyll a Chlorophyll a is essential for most photosynthetic organisms to release chemical energy but is not the only pigment that can be used for photosynthesis. One molecule of chlorophyll a forms the reaction centre. It absorbs energy from wavelengths of violet and red light.

The molecular structure of chlorophyll a consists of a chlorin ring, whose four nitrogen atoms surround a central magnesium atom, and has several other attached side chains and a hydrocarbon tail.

This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and pro chlorophytes because of its role as primary electron donor in the electron transport chain.

Chlorophyll b Chlorophyll b helps in photosynthesis by absorbing light energy.It is more soluble than chlorophyll a in polar solvents because of its carbonyl group. Its color is yellow, and it primarily absorbs blue light. In land plants, the light harvesting antennae around photosystem II contain the majority of chlorophyll b.

Xanthophylls Xanthophylls (originally phylloxanthins) are yellow pigments that form one of two major divisions of the carotenoid group. Their molecular structure is similar to carotenes, which form the other major carotenoid group division, but xanthophylls contain oxygen atoms, while carotenes are purely hydrocarbons with no oxygen.

Like other carotenoids, xanthophylls are found in highest quantity in the leaves of most greenplants, where they act to modulate light energy and perhaps serve as a non-photochemical agent to deal with excited chlorophyll.

Carotenes Carotene is an orange photosynthetic pigment important for photosynthesis. Carotenes are all coloured to the human eye.

Carotenes contribute to photosynthesis by transmitting the light energy they absorb to chlorophyll. They also protect plant tissues by helping to absorb the energy from singlet oxygen, an excited form of the oxygen molecule O2 which is formed during photosynthesis.

EXPERIMENT Chlorophyll content in various plant species

Aim: To compare and study the chlorophyll content in different plant species.

Requirements

 Fresh leaves of spinach  Mint  Methi leaves  Winkarosea  Banana leaves  Separating funnel  Measuring cylinder  Beakers  Vials

Chemicals required:  Acetone

 Diethyl ether  Petroleum ether  Methyl alcohol  Calcium carbonate  Potassium hydroxide  Distilled water

PROCEDURE  Take 10g of fresh leaves in pestle and crush it with 4ml 80% acetone. Add a little CaCO3 and again crush it. Filter the extract in a Buchner funnel. The filtrate is called acetone extract and it is rich in chlorophyll and carotenoids.  Take 4ml of the acetone extract and add petroleum ether. Shake funnel gently.  Add water and shake again. Two layers will be formed. Upper containing petroleum ether will contain chlorophyll a and carotene.

 The lower acetone water layer is discard.  To the upper remaining layer add 4ml 92% methyl alcohol. Shake the funnel and let it separate into two layers. Upper layer contains petrol and ether rich in chlorophyll a and carotenoids; lower is the methyl alcohol layer rich in chlorophyll b and xanthophyll pigments.



To the upper layer add 1.5ml 30% methyl alcohol and KOH. Add water and shake funnel.

 Two layers are obtained. Upper has chlorophyll a and lower has carotene.

 To the lower methyl alcohol layer add 5ml diethyl ether and shake. Add water slowly 1ml at a time. Two layers are obtained. The upper layer is the diethyl ether layer and lower contains methyl alcohol.  Discard lower layer.  To the upper layer add 1.5ml 30% methyl alcohol-KOH. Shake funnel and add water.  Two layers are obtained.

 Upper layer contains chlorophyll b and lower contains xanthophyll.  Collect the samples, weigh them and note the amount of chlorophyll pigments present in them.

OBSERVATION TABLE

S

TYPE OF LEAF

WEIGHT OF PIGMENT

NO CHLOROPHYLL

CHLOROPHYLL

CAROTENE

XANTHOPHYLL

1

SPINACH

A 3.4

B 0.6

4.6

4.82

2

FENUGREEK

1.76

0.5

2.92

3.16

3

BOUGAINVILLA

1.75

0.37

2.23

2.37

4

MINT

3.4

1.02

4.73

4.63

5

CABBAGE

3.59

0.55

5.3

4.9

RESULT Each type of leaf has various levels of pigments based on its genetic constitution, exposure to light, age, season, wind, precipitation, photosynthetic rate, respiration rate, and protein level. Out of the five leaves tested, cabbage had the highest level of Chlorophyll a, and Bougainvillea the lowest. The highest level of Chlorophyll b was present in mint while the lowest level was present in mint while the lowest level was present in Bougainvillea. Cabbage had the most Carotene and Bougainvillea had the least. Cabbage also had the greatest level of Xanthophylls and Bougainvillea had the least. As seen clearly, chlorophyll value decreases with leaf senescence.

BIBLIOGRAPHY

* www.wikipedia.org * www.google.com * www.howstuffworks.com * www.letsmakesciencefun.com