Photosynthetic Pigments: Definition, Meaning Types, Examples, Functions

What Are Photosynthetic Pigments?

Photosynthetic pigments are the light-absorbing molecules used to enhance the process of photosynthesis. Photosynthetic pigments include, mainly, chlorophyll a, chlorophyll b, carotenoids, and phycobilins, contained in the chloroplast of plant cells and other photosynthetic organisms. They capture light energy at specific wavelengths and convert it into chemical energy used to power the synthesis of glucose from carbon dioxide and water.

Photosynthetic pigments are required to increase the photosynthetic efficiency since they capture light energy and trigger the process by which it is converted into chemical energy. Chlorophyll a is the main photosynthetic pigment capturing light energy and passing it on in a form that the plant can use. Carotenoids and chlorophyll b broaden the wavelength range absorbed and protect against photodamage. If missing, plants would not be able to adequately harness the energy of sunlight and therefore, the energy production and growth would be reduced.

Types of Photosynthetic Pigments

Chlorophylls are the major photosynthetic pigments involved in the absorption of light energy. They participate in light-dependent photosynthetic reactions, converting light energy into chemical energy.

Chlorophylls

The different types of chlorophyll are:

Chlorophyll a

This is the most abundant and important pigment of photosynthesis. Chlorophyll mainly absorbs light in the blue-violet and red portions of the visible spectrum. It participates directly in the conversion of light energy into chemical energy and is present in all photosynthetic organisms.

Chlorophyll b

This is a pigment that complements the light absorbed by chlorophyll in the blue and red-orange regions, thus broadening the spectrum of light that can be used. It is mainly found in green plants and green algae. Its function appears to pass the captured energy on to chlorophyll a.

Chlorophyll c, d, and e

These forms of chlorophyll are found in certain algae and cyanobacteria. Chlorophyll c is present in brown algae and the diatoms. Chlorophyll d is found in red algae, and chlorophyll e in some green algae. They perform the same functions as chlorophyll but are adjusted to other light conditions.

Carotenoids

Carotenoids are explained below:

Carotenes

These include a class of carotenoids that appear orange, including β-carotene, which is a precursor to vitamin A in animals. Carotenes help in light absorption and photoprotection.

Xanthophylls

These are yellow carotenoids which take part in protecting the photosynthetic apparatus from too much light energy. They take part in dissipating excess energy as heat. Examples include the pigments lutein and zeaxanthin.

Phycobilins

Phycobilins are explained below:

Phycocyanin

This is a blue pigment that absorbs orange and red light, hence aiding photosynthesis in cyanobacteria and some algae. It augments light absorption in low-light conditions.

Phycoerythrin

This red pigment absorbs blue and green light and provides good complementarity with phycocyanin. At depths below 10 meters in water, by the time it reaches this depth, most of the other light has been already absorbed. So blue-green light penetrates far better; hence, it becomes useful.

Functions of Photosynthetic Pigments

The major functions of photosynthetic pigments are given below:

Significance of Photosynthetic Pigments

The significance of photosynthetic pigments includes:

• The pigments increase the range of light absorption and hence, improving the photosynthetic efficiency.

• It protects from photooxidative damage under intense light conditions.

• It enables photosynthesis under diverse environmental conditions like deep water and shade.

• It facilitates the electron transfer and formation of ATP in photosystems.

Photosynthetic Pigments NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Types of photosynthetic pigments

• Functions of photosynthetic pigments

Practice Questions for NEET

Q1. The energy of light is contained in

1. Electrons

2. Neutrons

3. Bosons

4. Photons

Correct answer: 4) Photons

Explanation:

Photons contain the energy of light.

Light particles with electromagnetic energy are called photons. A photon's energy is inversely proportional to its wavelength and directly proportional to its frequency. Accordingly, light with a higher frequency (like violet or ultraviolet light) has more energy per photon than light with a lower frequency (like red or infrared light).

Hence, the correct answer is option 4) Photons.

Q2.Which of the following is correct w.r.t protochlorophyll?

1. It is soluble in water.

2. It is insoluble in organic solvents.

3. It lacks two hydrogen atoms.

4. It lacks two carbon atoms.

Correct answer: 3) It lacks two hydrogen atoms.

Explanation:

Protochlorophyll is a key intermediate in the synthesis of chlorophyll, the vital green pigment responsible for photosynthesis in organisms such as plants, algae, and cyanobacteria. Its primary function is to evolve into chlorophyll via enzyme-driven processes.

- Precursor Role: It directly converts to chlorophyll a, a critical step in the formation of photosynthetic pigments.
- Dark-grown Plant Presence: Protochlorophyll exists in etiolated, or light-starved, seedlings before light exposure.
- Light-dependent Transformation: Light is indispensable for its conversion into chlorophyll a, mediated by protochlorophyllide oxidoreductase (POR).
- Lipid-Soluble Nature: Like chlorophylls, it is soluble in fats and resides in organelles known as plastids, specifically proplastids and etioplasts.

Hence, the correct answer is option 3) It lacks two hydrogen atoms.

Q3.Etiolation is seen in

1. Monocots kept in light.

2. Dicots kept in the dark.

3. Gymnosperms kept in the dark.

4. All of these

Correct answer: 2) Dicots kept in the dark.

Explanation:

Etiolation is a distinctive condition in plants exposed to absolute darkness or minimal light, leading to altered growth patterns aimed at light maximization. Characteristic etiolated plant features are:

1. Chlorophyll-deficient, resulting in pale yellow or white foliage.
2. Elongated stems, an adaptation to reach light sources.
3. Reduced leaf size or underdevelopment.
4. Chlorosis, the absence or insufficient chlorophyll.

This phenomenon occurs as light is vital for chlorophyll synthesis and typical plant development. In light-scarce environments, plants transform to locate light, which manifests in these specific traits.

Hence, the correct answer is option 2) Dicots kept in the dark.

Also Read:

• MCQs on Photosynthetic Pigment

• C4 Pathway

• Carbon Fixation

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