Chlorophyll Structure - Definition, Types, Biosynthesis, Uses

What is Chlorophyll?

Chlorophyll is a green pigment in plants, algae, and cyanobacteria that accounts for their green colour. It is very essential to photosynthesis, the process by which light energy is converted into the form of chemical energy stored as glucose.

Chlorophyll mainly absorbs light from the blue and red parts of the spectrum but reflects green light. Thus, giving off its green color in plants. This pigment has a significant role in capturing light energy and then transferring it to its energy converters within the plant cells, changing it into chemical energy that drives the synthesis of the organic molecules sustaining the growth of plants and ultimately supporting the food chain.

Structure of Chlorophyll Molecule

Chlorophyll is a complicated molecule, but the structure includes mainly a porphyrin ring with a long hydrophobic phytol tail.

Porphyrin Ring

In the molecular structure of chlorophyll, there exists a porphyrin ring that includes four nitrogen-containing pyrrole rings, which act as light absorbers. These nitrogen atoms around a central magnesium ion. This ring acts as the light-absorbing centre of the molecule and responsible for capturing photons and initiating electron excitation.

Central Magnesium Ion (Mg²⁺)

This includes a magnesium ion at the centre of the ring for capturing light energy. It plays a crucial role in absorbing light energy. It helps in electron excitation and transfer during light reactions. Without Mg²⁺, chlorophyll loses its green color and photosynthetic activity.

Phytol Tail

This phytol tail will help anchor the chlorophyll molecule within the lipid membranes of the chloroplasts and more precisely in the thylakoid membranes where photosynthesis occurs

Types of Chlorophyll

The different types of chlorophyll are:

Chlorophyll a

It is considered the most important pigment in photosynthesis due to the effective forms that enable it to absorb light energy from the blue-violet and red portions of the electromagnetic spectrum. This pigment participates in the light-dependent reactions of photosynthesis and it is responsible for converting light energy into chemical energy.

Chlorophyll b

This is a light-harvesting or accessory pigment that broadens the ability of the plant to capture light energy by absorbing blue and red-orange light. It transfers the acquired light energy into chlorophyll and hence enhances the efficiency of photosynthesis.

Chlorophyll c and d

Types of chlorophyll are found in some algae like brown algae diatoms, and red algae. Modified structures enable them to absorb light at different wavelengths. As such photosynthesis occurs in these sea algae in the various water environments where the conditions are unlike those on land.

Role of Chlorophyll in Photosynthesis

The role of chlorophyll in photosynthesis is:

• Light Absorption: It captures solar energy for the conversion into chemical energy.

• Energy transfer: The excited electrons drive the formation of ATP and NADPH.

• Oxygen release: It is indirectly responsible for the evolution of oxygen via water splitting.

• Photochemical Conversion: It converts light energy into stable chemical compounds like sugars

Summary – Chlorophyll Structure & Function

This table shows the components of the chlorophyll and their functions:

Chlorophyll NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Structure of Chlorophyll

• Types of Chlorophyll

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

Recommended video on "Chlorophyll Structure"