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Pigments Involved in Photosynthesis

This study material briefs about pigments involved in photosynthesis like chlorophyll, carotenoids, xanthophylls, and anthocyanins. These pigments involved in photosynthesis absorb a broad spectrum of light waves.

Introduction

The process of converting light energy into chemical energy with the help of specific chemical reactions is called photosynthesis. Pigments are chemical compounds located in the leaves of plants. They play a significant role in photosynthesis by absorbing and reflecting the light waves with specific wavelengths. These different wavelengths differentiate the colour of the leaf from each other, due to which different plants have different leaf colours. Pigments like chlorophyll contribute towards the green colour of the leaf and absorb red and blue light most strongly. Pigments other than chlorophyll like carotenoids make the leaf’s colour red, orange, or yellow. Along with that, Phycobilins contribute blue-green and reddish colour to algae, and xanthophyll helps make the leaf pale-yellow green. Anthocyanins pigment is responsible for giving a reddish output on the leaf.

How does chlorophyll contribute to the process of photosynthesis?

Located within the chloroplasts, chlorophyll is a green pigment present in the deep sections of the leaf called the thylakoid membrane, which is located inside chloroplasts. Chlorophyll plays an essential role in photosynthesis because it comes in handy in both chemical reactions and the light reaction of the plant. The chemical structure of chlorophyll comprises porphyrin rings and a hydrocarbon side chain. The porphyrin rings consist of double bonds and triple bonds and can be located on molecules that possess the ability to absorb visible light. Chlorophyll assists the process of photosynthesis in two parts which include light reactions and the Calvin cycle. Chlorophyll absorbs light energy during the light reaction stage, thus exciting some electrons in the pigment molecule. These pigment molecules are of higher energy levels and leave the chlorophyll, bypassing a long series of molecules. The reaction thus results in generating high energy ATP (Adenosine Triphosphate) and an enzyme(NADPH). Further, oxygen is released as a byproduct that passes into the atmosphere through tiny pores present on the leaf. The left-behind ATP molecules and NADPH control the second stage, known as the Calvin cycle, and generate glucose using atmospheric carbon dioxide.

Accessory pigments

Accessory pigments are compounds capable of absorbing light and are primarily located in photosynthetic organisms. It comprises mainly chlorophyll A, which helps facilitate the absorption scale for different colours and masks the ability of accessory pigments. While chlorophyll B and C contribute by reflecting the varying shades of green light, making the leaf look different from others. If the extent of chlorophyll A becomes less, then the accessory pigments move by, changing the colour of the leaf. In photosynthetic organisms, light-absorbing pigments play a critical role in photosynthesis. Light absorbing reactions are classified into two types: cyclic and non-cyclic. In cyclic reactions, the electron is displaced from the photosystem to make its way to the electron acceptor molecules. After reaching the acceptor molecules, the electron is ejected again to the same photosystem, thus creating a cyclic loop. In noncyclic reactions, the photon is captured by the antennas of light-harvesting complexities of the photosystem and other accessory pigments. Hence, accessory pigments play an essential role in absorbing the light and transporting the energy created to the primary stain, chlorophyll.

Types of accessory pigments

The molecular structure of accessory pigments is slightly varying from chlorophyll A because chlorophyll stops the accessory pigments from changing the colour of the leaf. But as the level of chlorophyll drops, mainly at the fall of the year, accessory pigments make their way to the top by changing the leaves’ colour. The colourings responsible for making colour changes are:-

Chlorophyll b

Chlorophyll B emits green light by mostly absorbing the blue and red light coming in from the atmosphere. It is synthesised by adding chlorophyllide B into phytyl diphosphate. Its chemical formula is C₅₅H₇₀MgN₄O₆ with a molecular weight of 907.5

Carotenoids

Carotenoids, a precursor of Vitamin A, are responsible for transmitting orange, yellow and red light waves. Also called tetraterpenoids, this pigment can be produced from plants, algae, fats and other building blocks of the organism. They are fat-soluble molecules that can dissipate radiant energy in excessive amounts. Its molecular formula is C₄₀H₅₆ and its molecular weight is 536.9

Xanthophyll

Xanthophyll pigments act as an antioxidant by passing light energy to chlorophyll A. It produces a yellow colour in the leaves at the fall of the year and can donate or share electrons. Its molecular formula is C₄₀H₅₆O₂ with a molecular weight of 568.9

Anthocyanin

Anthocyanin is a water-soluble molecule that is stored in the plant cell vacuole. It absorbs blue-green light and emits reddish and violet light into the environment. Autumn leaves appear reddish in colour due to the anthocyanin compound. Its chemical formula is C₁₅H₁₁O⁺.

Antenna pigments

When photosynthetic pigments like chlorophyll B and carotenoids react with protein, the resultant product is a tightly packed antenna-like structure capable of capturing incoming photons. Antenna pigments absorb radiant energy to pump photons into reaction centres as a part of the photosynthetic process. It can be used for manufacturing ATP molecules by exciting an electron with the help of a photon and passing it to the nearby acceptor molecule.

Conclusion

For executing smooth photosynthesis, pigments are necessary. It may include accessory pigments, antenna pigments, and chlorophyll, which plays the most significant part in the process. Along with chlorophyll, pigments like Carotenoids, Xanthophyll, Anthocyanin, Phycobilins etc., are equally crucial for photosynthesis. They are energy-rich organic molecules, capable enough to drive the global carbon cycle and create leaves that are deeply coloured. Hence, pigments involved in photosynthesis is an important topic to be studied when discussing the prospective examination as it covers many critical points and issues.

Frequently asked questions

Get answers to the most common queries related to the NEET UG Examination Preparation.

What are pigments and why is it important?

Ans. Pigments are chemical compounds located in the leaves of plants. They play a significant role in photosynthesis...Read full

Name the pigment which is responsible for different colours in leaves.

Ans. Pigments like chlorophyll contribute towards the green colour of the leaf and absorb red and blue light most st...Read full

What role does chlorophyll play in the photosynthesis process?

Ans. Chlorophyll plays an essential role in photosynthesis because it comes in handy in both chemical reactions and ...Read full

What are accessory pigments? What is the importance of chlorophyll A, B and C?

Ans. Accessory pigments are compounds capable of absorbing light and are primarily located in photosynthetic organis...Read full

How is antenna pigment formed? What is its importance.

Ans. When photosynthetic pigments like chlorophyll B and carotenoids react with protein, the resultant product is a ...Read full