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

Definition Of 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. Had it not been for the presence of chlorophyll, the solar energy-to-chemical energy conversion would not have taken place, 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

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. 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:

Photosynthesis

Process of light absorption and energy conversion.

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 the light-dependent reactions of 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.

Role In Energy Transfer

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 In Plants

In plants, chlorophyll has a role in photosynthesis in various forms, from terrestrial to aquatic plants. The principal pigments capturing light energy to synthesise carbohydrates in the chloroplast of the leaf cells are chlorophyll a and b.

This arrangement of chlorophyll a and b in chloroplasts within the mesophyll cells of the leaves is quite common in terrestrial plants and enables them to capture optimal light from the sun. Aquatic plants also contain these chlorophylls but do so with adaptations to include additional pigments or different types of chlorophylls that allow the plants to survive underwater with low light intensities and different spectra.

In Algae And Cyanobacteria

In algae, there can be variations in chlorophyll types. For example, green algae contain chlorophylls a and b, typical for higher plants; red algae have chlorophyll a, but also chlorophyll d, which captures light better for photosynthesis in deeper or more turbid water.

Cyanobacteria, known simply as blue-green algae, are mostly chlorophyll a, but they also have several other pigments; many of them are phycobilins, such as phycocyanin and phycoerythrin, and they help to absorb more light. These pigments allow cyanobacteria to exist in shallow and more deep environments in water, where light conditions change gradually.

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