Biological Pigments in Plants: Definition, Types and Examples

What Are Biological Pigments?

Biological pigments are any of the naturally occurring compounds that absorb and reflect wavelengths of light to give colour and make different physiological functions within living organisms possible. The pigments play a fundamental role in photosynthesis in plants by capturing the energy from light and then storing it in the form of chemical energy.

The article discusses different types of biological pigments, such as chlorophylls, carotenoids, and phycobilins, in connection to their role in the health functions of plant pigment. Their contribution to the effectiveness of photosynthesis via absorption and photoprotection shall also be discussed.

Types of Biological Pigments in Plants

The different types of biological pigments found in plants are:

Chlorophyll

The chlorophyll is the most abundant green pigment and vital for photosynthesis.

Types

The most widely distributed forms are chlorophyll a, which plays a part in electron transfer during the realisation of light-dependent reactions in photosynthesis, and chlorophyll b, which captures light energy and extends the spectrum of absorbed light. Such forms as chlorophyll c, d, and e are well spread in certain algae. Their function is the same as in the above cases, only adapted to some other light conditions.

Functions

Chlorophylls absorb light energy emanating from the blue-violet and red ends of the visible spectrum and convert light energy into chemical energy. The chemically converted form of light energy gets stored and put to use again in the synthesis of glucose from carbon dioxide and water.

Distribution

Chlorophylls are found in plant cells. In plant cells, they are mainly distributed in the chloroplasts and more clearly in the thylakoid of the chloroplast where light reactions take place.

Carotenoids

Carotenoids are the accessory pigment that absorbs blue-green light and provides photoreception.

Types

There are two types of carotenoids: carotenes (e.g., β-carotene) which are hydrocarbon pigments and xanthophylls (e.g., lutein) which are oxygenated carotenoids.

Functions

They absorb bluish-green light, which is not absorbable by chlorophyll, and then transfer the energy to the chlorophyll. Also, they serve to protect the photosynthetic apparatus from too much harmful light energy by scavenging it and dissipating it as heat.

Examples (β-Carotene, Lutein)

One such carotenoid is beta-carotene, which is a naturally occurring precursor to vitamin A, important in nutrition. Another is lutein, which protects the plant tissue from light damage.

Anthocyanins

Anthocyanins are water soluble pigments that are responsible for red, blue and purple colours in flowers, fruits and leaves.

Structure

The anthocyanins are a water-soluble group of pigments having the general structure of a glycosylated flavonoid. It underlies the colour in the red, purple, and blue colours in plants. Herein, the precise chemical structure of the individual anthocyanins and also its specific glycosylation pattern are variable.

Functions

The colours of anthocyanins are bright, playing a double role in defending the plant against herbivores and again attracting pollinators.

Distribution

They occur in different tissues of the plants like fruits, flowers, and leaves. Being part of the pigment system, they colour the plants and interact with the environment.

Flavonoids

These are pigments implicated in plant pigmentation, UV protection, and signalling. The subtypes, such as flavonols and flavones, are implicated in the defence mechanisms of the plant and in attracting pollinators. They also serve as signalling molecules in plant microbe interactions.

Phytochromes

Light receptor pigments control the response of plants to the presence or absence of light. This response regulates seed germination, shade avoidance and time of flowering. It exists in two forms i.e., Pr (inactive) and Pfr (active), interconvertible by light.

Cryptochromes

Cryptochromes are another pigment, which acts as a receptor of blue light. It is controlling growth and developmental processes in response to changes in light. It also plays roles in the expansion of leaves and opening of stomata.

Functional Significance of Pigments

The significance of the biological pigments are:

• Enable maximum light absorption.

• Regulate plant growth and development through light absorption.

• Influence the colour of flowers and fruits for reproduction.

• Maintaining the photosynthetic efficiency and ecological adaptations.

• Provide photoreception under high light conditions.

Summary Table – Plant Pigments and Their Roles

This table summarizes the different biological pigments, their role, color and location.

Biological Pigments NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Types of biological pigments

• Functions of biological 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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