Difference Between Chlorophyll a and Chlorophyll b

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Green plants and certain algae survive by producing energy from sunlight, water, and carbon dioxide through photosynthesis. In this process, light energy is transformed into chemical energy. In photosynthesis, water, and carbon dioxide, are converted into glucose, in the presence of sunlight; and oxygen is released into the environment. Besides playing a vital role in sustaining the life of plants and other organisms, photosynthesis supports the whole world by regulating oxygen and carbon dioxide levels. Photosynthesis sustains the plant life, which in turn, is essential to maintain the food-chains and food-webs.

When you look into the process of photosynthesis, you will see that the primary pigment that facilitates the process is the green pigment called chlorophyll. This pigment is found in certain microorganisms like cyanobacteria and inside thylakoid membranes of chloroplasts of plant cells. These pigments absorb the red and blue wavelength light rays from the sunlight, which is necessary to initiate the process of photosynthesis.

The chloroplasts contain various types of chlorophyll that contribute differently to the process of photosynthesis. These types of chlorophyll are as follows.

  • Chlorophyll a - It is the most abundant type of chlorophyll, which absorbs light rays of wavelengths of 429 nm and 659 nm most effectively.

  • Chlorophyll b - It is a type of accessory pigment responsible for passing on light energy to chlorophyll a. It is found in plants and green algae. It absorbs the light rays of wavelengths 455 nm and 642 nm.

  • Chlorophyll c - This chlorophyll pigment is found predominantly in marine algae and absorbs light rays of wavelength 447-452 nm.

  • Chlorophyll d - This pigment is mainly found in cyanobacteria, and they absorb light rays of wavelengths outside the optical range such as 710 nm.

Both chlorophyll a and b play an imperative role in photosynthesis in plants. The primary pigment responsible for photosynthesis is chlorophyll a, and b absorbs sunlight to pass it on to chlorophyll a.

The difference between chlorophyll a and chlorophyll b is tabulated below.

Difference Between Chlorophyll A and B

Chlorophyll A

Chlorophyll B

It is the principal pigment involved in photosynthesis.

It is an accessory pigment that helps in photosynthesis.

All plants, algae, bacteria, cyanobacteria, and phototrophs contain chlorophyll a.

Chlorophyll b is only present in green plants and algae.

It absorbs a range of violet-blue light and orange-red light from sunlight.

It only absorbs orange-red light from sunlight.

The absorption range of light is 430 nm to 660 nm for chlorophyll a. Its rate of absorption is also high.

The light rays of wavelengths 450 nm to 650 nm are absorbed by chlorophyll b. The rate of absorption is low.

Chlorophyll a absorbs red wavelengths more.

Chlorophyll b absorbs violet-blue light.

Chlorophyll a reflects blue-green light.

Chlorophyll b reflects orange-red light.

The chlorine ring of Chlorophyll a has  a methyl group in the third position.

In the chlorophyll b structure, there is an aldehyde attached to the chlorine ring in the third position.

Its structure makes it soluble in petroleum ether. It also has low solubility in polar solvents.

The structure of chlorophyll b makes it soluble in methyl alcohol. It has a high solubility in polar solvents.

It has a CH3 side group in the porphyrin ring.

It has a CHO group other than CH3 in the porphyrin ring.

The molecular formula of chlorophyll a is C55H72O5N4Mg. (Molecular weight is 839.51gmol).

The chlorophyll b formula is C55H70O6N4Mg. (Molecular weight is 907.49g/mol).

Almost 3/4th of chlorophyll found in plants is of this variant.

It accounts for only 1/4th of the chlorophyll present in plants. 

The core proteins’ antenna array reacts in chlorophyll a.

Chlorophyll b regulates the size of the antenna of the photosystem.

From the above table, Chlorophyll a vs. Chlorophyll b comparison must have become easier to understand.

The following diagram shows the structure of chlorophyll a and b and how both work within a photosystem.

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Fun Facts About Chlorophyll

  • Chlorophyll is Good for Your Health

Many people consume chlorophyll as a health supplement, and medical studies suggest it has several health benefits. It is said to be beneficial in slowing signs of aging, treatment of acne, and fighting anemia of hemoglobin deficiency.

Studies also suggest that it helps fight cancer, remove body odour, and speeds up the healing of wounds. However, it is unsafe to consume supplements without asking your doctor first, and further studies are going on in this field.

  • Animals That Use Photosynthesis

Apart from plants and microorganisms like algae, some animals have also utilized photosynthesis for additional energy. For instance, the oriental hornet uses a pigment called xanthopterin for converting solar energy into electricity. The spotted salamander has a symbiotic relationship with algae and uses photosynthesis for additional oxygen supply. A species of sea slug also steals chloroplasts from marine algae to carry out photosynthesis with its own cells.

FAQ (Frequently Asked Questions)

Q1. How do Non-Green Plants Perform Photosynthesis?

Answer: Most plants, irrespective of their appearance, perform photosynthesis, and contain chlorophyll. Certain leaves and ornamental plants may not appear green because they contain other pigments like anthocyanin or carotenoid. These pigments make leaves appear orange, reddish, or even purple depending on the wavelengths of the light they absorb and reflect, similar to chlorophyll. These pigments mask the overall green colour of the chlorophyll present in the leaves. Therefore, the process of photosynthesis takes place just the same in these plants as well. Even in plants with white leaves, there is hidden chlorophyll, and it is only masked by light reflection. The only exceptions to these are plants that are parasitic and do not contain chlorophyll. They depend on other plants that perform photosynthesis to obtain energy.

Q2. Do all Plants Photosynthesize Light the Same Way?

Answer: No, there are different types of photosynthetic processes. The most commonly used and studied process of photosynthesis is the C3 photosynthesis. This is the most efficient method suitable for normal temperature, light, and moisture conditions. It uses an enzyme called RUBISCO that collects CO2 during the day and converts 75% of it into a 3-carbon compound.

Similarly, in the C4 photosynthetic process, the carbon is converted into a 4-carbon compound. This process occurs in extremely hot conditions like in deserts, where the sunlight is also in excess. The C4 photosynthesis process is naturally designed to use water more efficiently and reduces transpiration. This is achieved by an enzyme called PEP Carboxylase in addition to RUBISCO.

CAM or the Crassulacean Acid Metabolism is the third type of photosynthesis wherein the CO2 is stored in the acid form before conversion to energy. This process produces glucose from the stored carbon dioxide. Therefore these plants grow very slowly compared to other plants. Nevertheless, this process enables them to survive in extreme conditions like deserts.