Chlorophyll: Definition, Function, Facts, Formula, Structure, Diagram

What Is Chlorophyll?

Chlorophyll is the green pigment in plants, algae, and cyanobacteria. It is responsible for photosynthesis. The basic definition would be a pigment that can absorb light energy from the sun to create chemical energy. Light is absorbed in both the blue-violet and red areas of the spectrum; what is reflected is green in colour, which explains the green colour of plants.

This pigment is a major player in the photosynthetic process, as it enables the transfer of absorbed light energy to the reaction centres that use this energy for the synthesis of glucose from carbon dioxide and water. The presence of chlorophyll has made it possible to convert the solar energy-to-chemical energy, and it is this energy conversion that sustains most life forms existing on Earth.

Structure Of Chlorophyll

The structure of chlorophyll is explained below:

Basic Structure

The basic structure of chlorophyll consists of three major components:

Porphyrin ring and its components

Chlorophyll molecules have a very complicated structure, with a porphyrin ring at its centre. This large, cyclic arrangement comprises carbon, hydrogen, and nitrogen atoms. Right at the centre of this ring is located a magnesium ion, an element central to the ability of the pigment to absorb light and undergo photosynthesis.

Phytol tail

Attached to the porphyrin ring is a phytol tail, which is a long hydrocarbon chain. This chain anchors the chlorophyll molecule within the thylakoid membrane of the chloroplast.

Central magnesium ion

What makes chlorophyll capable of capturing light energy is the association of the porphyrin ring with a magnesium ion.

Types Of Chlorophyll

The types of chlorophyll are:

Chlorophyll a

This is the major pigment responsible for the light-dependent reactions of photosynthesis. It is efficient in absorbing light at the blue-violet and red ends of the visible spectrum. It reflects green light, which means that it is the basis of green colouration in plants. Chlorophyll a is crucial in the primary conversion of light energy to chemical energy.

Chlorophyll b

Chlorophyll b acts as an accessory pigment to the light-harvesting complex, picking out light in the parts of visible blue and red-orange areas of the spectrum. This helps to increase the ability of light that can be used in photosynthesis, feeding the collected energy into chlorophyll.

Chlorophyll c and d

Chlorophyll c and d are found in some algae. Chlorophyll c has a slightly different structure than chlorophyll a and is adaptations to absorb light in different aquatic environments, and chlorophyll d is a modified form found in red algae, which captures light in the deeper or shadier water, while other types of chlorophyll cannot do as effectively.

Function Of Chlorophyll

The function of chlorophyll is described below:

Light Absorption

Chlorophyll plays a central role in the photosynthetic process by being responsible for light energy absorption, mainly within the blue-violet and red portions of the spectrum. The energy of this light that gets absorbed by the chlorophyll molecule excites electrons to begin a series of reactions involved in the light-dependent phase of photosynthesis

Role in Photosynthesis

In this process, the energy is transferred to electron carriers in the thylakoid membrane by the excited electrons, commonly known as the electron transport chain, which produces energy-rich molecules such as ATP and NADPH for the light-independent reaction.

Energy Conversion

Chlorophyll participates in the production of ATP and NADPH for glucose production in the Calvin cycle. In light-dependent reactions, light is absorbed by the molecule of chlorophyll, which leads to the transfer of excited electrons through a series of proteins in the thylakoid membrane, thus ultimately leading to the production of ATP through photophosphorylation and reducing NADP+ to NADPH.

They then migrate into the stroma of the chloroplast and serve as both the energy and reducing power for carbon fixation and the synthesis of carbohydrates in light-independent reactions.

Chlorophyll In Different Organisms

Chlorophyll in different organisms is given below:

Chlorophyll NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Types of Chlorophyll

• Chlorophyll in different organisms

Practice Questions for NEET

Q1. Chlorophyll ‘b’ is found in

1. All oxygen-releasing photosynthetic forms

2. All plants except fungi

3. All higher plants that photosynthesize

4. All higher plants and green algae

Correct answer: 4) All higher plants and green algae

Explanation:

Green algae and all higher plants, including trees, shrubs, and flowering plants, contain chlorophyll b. Chlorophyll b increases the range of light that plants may use as energy by absorbing light wavelengths that chlorophyll a cannot. This helps plants capture light energy for photosynthesis.

The reason the other choices are wrong is

• Since not all oxygen-releasing creatures (such as some bacteria) have chlorophyll b, the term "all oxygen-releasing photosynthetic forms" is overly general.

• All plants are wrong, except fungi, which lack chlorophyll because they are unable to carry out photosynthesis.

• Green algae, which also contain chlorophyll b, are not included in the list of higher plants that photosynthesize, which is overly restrictive.

Hence, the correct answer is option 4) All higher plants and green algae.

Q2. The chlorophyll ‘a’ molecule at its carbon atom 3 of the pyrrole ring II has one of the following:

1. Aldehyde group

2. Methyl group

3. Carboxylic group

4. Magnesium

Correct answer: 2) Methyl group

Explanation:

A methyl group (–CH₃) is present at carbon atom 3 of the pyrrole ring II in the structure of chlorophyll a. The main pigment in photosynthesis, chlorophyll a, is made up of a porphyrin ring with a magnesium ion in the middle. One of the main characteristics of chlorophyll a that sets it apart from chlorophyll b, which also has an aldehyde group at this location, is the presence of the methyl group at this particular location.

The reason the other choices are wrong is

• Chlorophyll b, unlike chlorophyll a, contains the aldehyde group.

• Chlorophyll a does not have a carboxylic group at this location.

• Although it is not found at carbon atom three of the pyrrole ring, magnesium is the core ion of the chlorophyll molecule.

Hence, the correct answer is option 2) Methyl group.

Q3. Which is the vital element constituent of the ring structure of chlorophyll?

1. Magnesium

2. Zinc

3. Chlorine

4. Calcium

Correct answer: 1) Magnesium

Explanation:

Magnesium (Mg) is a crucial component of chlorophyll's ring structure. The core of the chlorophyll molecule contains magnesium. It facilitates the absorption of light by chlorophyll, which is essential for photosynthesis and the process by which plants produce food. Chlorophyll in plants would not function correctly without magnesium.

Hence, the correct answer is option 1) Magnesium.

Also Read:

• MCQs on Types of Chlorophyll

• Photosynthetic Pigments

• CAM Plants

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