Why is Chlorophyll Essential for Photosynthesis?

Why is Chlorophyll Essential for Photosynthesis?

Chlorophyll is Essential for Photosynthesis because the Chlorophyll absorbs the electromagnetic light energy from the Sun and produces glucose through a chemical reaction or Photosynthesis. Photosynthesis is the process of nutrition that converts solar energy into chemical energy in the form of Glyceraldehyde 3-phosphate (G3P) in phototrophs with chlorophyll.  Chlorophyll pigments, water, sunlight and carbon dioxide are the main four substances that are necessary for photosynthesis. Chlorophyll, the green pigments found in chloroplasts of plants and algae and in mesosomes of cyanobacteria, can absorb solar energy from sunlight and the most vital organic chemical for phototropic nutrition.

What is Chlorophyll?

Chlorophyll is the green-coloured pigment found in Chloroplast. Chloroplasts are a type of Plastid, a type of cell organelles. Plastids are mainly three types.

  • Chloroplast: Chloroplast Contains chlorophyll pigment and carotenoids and it is the type of plastid that takes part in photosynthesis.
  • Chromoplast: Chromoplast Contains pigments like carotene and xanthophylls. Chromoplasts are responsible for the colour variations of flowers and fruits and also help in the pollination and dispersal of seeds.
  • Leucoplast: Leucoplasts are the type of plastids that are colourless and mainly functions as storage plastids. Leucoplasts are mainly three types. Amyloplasts stores starch, Proteinoplasts or aleuroplasts store proteins and Elaioplasts store fat or lipid.
Chroloplast
Chroloplast
Chlorophyll absorbs light from the red and blue parts of the light spectrum and reflects green light. This is why the plants appear green to us.

The function of Chlorophyll in Photosynthesis

Photosynthesis takes place in grana located in stroma within the thylakoid. Chlorophyll molecules are rooted in the thylakoid membranes of chloroplasts.

Photosynthesis Equation
Photosynthesis Equation

Structure of Chlorophyll 

Chlorophyll contains magnesium (Mg++), as a central metal atom. The magnesium atom is surrounded by a nitrogen based structure which is known as porphyrin ring. Chlorophyll contains a fifth pyrrole that forms the ring. This pyrrole absorbs solar energy.  The chlorophyll function like photosynthetic pigments, embedded in chloroplasts. These Chlorophyll are outstanding photosensitizer.

What is Photosensitizer?

Photosensitizers are the molecules which is capable to absorb light energy and transfer the energy into another nearby molecule. This absorption of light is occurred in visible spectrum or infrared spectrum, as any higher energy electromagnetic radiation may result in the photoelectric effect.

Types of Chlorophyll

  • Chlorophyll a is found in all beings that perform oxygenic photosynthesis like plants, algae, cyanobacteria.
  • Chlorophyll b is found in green algae.
  • Chlorophyll c is found in diatoms.
  • Chlorophyll d is only found in red algae.

Out of these types, Chlorophyll a and Chlorophyll  b are the most common type of Chlorophyll.

Chlorophyll a and Chlorophyll b

The photosynthetic reaction centers are found in two photosystem units – Photosystem I and Photosystem II. These are P700 and P680. Chlorophyll b and chlorophyll a are found here, respectively.

Similarities of Chlorophyll a and Chlorophyll b: They don’t emit the absorbed light energies.

Chlorophyll a and b are almost similar in features with small differences:

Chlorophyll a Chlorophyll b
There is a methyl (-CH3) group attached with third carbon in a side chain as the methanol surrounds it There is an aldehyde (-CHO) group attached with third carbon in a side chain as acetone surrounds it.
It is the primary photosynthetic pigment. It is an accessory photosynthetic pigment.
It absorbs orange-red and violet-blue rays from sunlight. It absorbs blue and red rays.
Colour: Bluish-green Colour: Olive green

Chlorophyll serves three main functions at the primary level of Photosynthesis:

  1. Chlorophyll Essential for Photosynthesis as Chlorophyll molecules gets excited after absorbing sunlight or solar energy.
  2. It transfers the absorbed light energy to the photosynthetic reaction centre through the resonance energy transfer process.
What is the resonance energy transfer process?

It is a radiation-less process to transfer energy via a virtually undetectable proton emitted by an excited chromophore and received by a normal chromophore.

  1. In the photosynthetic reaction centre, a specific pair of chlorophyll (Chlorophyll a and Chlorophyll b) receives those charged protons and extracts the charge from them via biosynthesis.

Charge Separation

It is a very complex reaction that occurs under the thylakoid membrane. The charge of the chlorophyll is being extracted in the photosynthetic reaction centres. This process is called charge separation. P680 and P700 then transfer the charge to a series of electrons extracted from water molecules. This process continues to create an electron transport chain. These electrons help to produce oxygen (O2) and a charged hydrogen atom (H+). Therefore the splitting of water occurs through the absorbed solar energy and the water molecule splits into hydrogen and oxygen through the release of energy. This process is known as Photolysis of Water.

 

Photolysis of Water
Photolysis of Water

ATP:

The chlorophyll pigments of P680 and P700 pumps the H+ ions all over the thylakoid membrane to produce ATP and NADPH.

ATP or Adenosine triphosphate and NADPH (Nicotinamide Adenine Dinucleotide Phosphate Hydrogen) are chemical compounds to store the energy collected from the sunlight and processed through photosynthesis. This energy is supplied to chloroplasts to make starch from carbon dioxide (CO2). This starch stores the energy collected by ATP and NADPH in fruits, roots and stem.

What is ATP?

ATP is the acronym of Adenosine triphosphate. It is an energy-carrying molecule found in the cells of all living organisms. ATP absorbs chemical energy from the breakdown of food molecules and releases it to run other cellular activities.

 

Why is chlorophyll needed for photosynthesis?

  1. It absorbs solar energy from sunlight.
  2. The charge is transferred through chlorophyll from the outer surface of leaves and green parts of a plant.
  3. The absorption of orange-red and violet-blue rays by chlorophyll is one of the optimal functions of photosynthesis. Chlorophyll does not emit these rays.
  4. Chlorophyll a transfers the energy with help of chlorophyll b.
  5. Chlorophyll b absorbs blue and red light and emits green in colour.
  6. The process of starch creation takes place in chloroplasts.
Photosynthesis
Photosynthesis
Chlorophyll Facts

  • The word ‘Chlorophyll’ is derived from the Greek word  χλωρός or ‘Chloros‘, which denotes ‘the green of new growth’ or ‘yellow-green’, and φύλλον  or ‘phyllon‘, means ‘leaf’.
  • Chlorophyll can also be used as a dye. The extracted chlorophyll a is used dye with the commercial name of ‘Natural Green 3’ or ‘E140’. Chlorophyll  is used in colouring food items and cosmetics.
  • The Chlorophyll molecule is a chelate molecule or the molecules which have a central metal ion (Magnesium) bonded to a large organic molecule.
  • Experimental studies define Chlorophyll as a photosensitizer and is used in dye-sensitized solar cells (DSSCs) as DSSCs mimic the photosynthesis process in green plants.
  • Absorption spectrum of Chlorophyll is between 450-475nam to 650-675 nm.

 

The article ‘Why is Chlorophyll Essential for Photosynthesis?’ will help you to understand the essential role of Chrlolophyll in Photosynthesis and give you a comprehensive idea on ‘Why is Chrlolophyll important in Photosynthesis?’.

 

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