23. Which one of the following is NOT a characteristic property of carotenoids?
(1)They possess complex porphyrin ring.
(2)They are integral constituent of thylakoid membrane.
(3) They are also called accessory pigments.
(4) They protect plants from damages caused by light.

The property that is NOT characteristic of carotenoids is (1) They possess complex porphyrin ring. Carotenoids are long-conjugated hydrocarbons, not porphyrin-based pigments like chlorophyll. Here’s a detailed explanation for each option.

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Properties of Carotenoids: What’s NOT Correct

Introduction

Key phrase: characteristic properties of carotenoids thylakoid accessory pigment photoprotection

Carotenoids are vital pigments in chloroplast thylakoid membranes that support photosynthesis and defend plants against excessive light. While they have several defining features, possessing a complex porphyrin ring structure is not among them.

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Explanation of Each Option

• (1) They possess complex porphyrin ring

  • NOT correct. Carotenoids are composed of long chains of conjugated double bonds (polyene structures), not porphyrin rings. Porphyrin rings are the hallmark of chlorophylls and heme proteins, not carotenoids.

• (2) They are integral constituent of thylakoid membrane

  • Correct. Carotenoids are embedded throughout the thylakoid membrane and tightly bound to photosynthetic complexes, assisting in light capture and protecting structural integrity.

• (3) They are also called accessory pigments

  • Correct. Carotenoids serve as accessory pigments by broadening the spectrum of light absorption for photosynthesis and funneling excess energy to chlorophyll.

• (4) They protect plants from damages caused by light

  • Correct. Carotenoids have a critical photoprotective role, quenching singlet oxygen and dissipating excess energy to prevent oxidative stress within the photosynthetic apparatus.

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Quick Facts About Carotenoids

• Structure: Polyene chain, no porphyrin ring.

• Location: Integral to thylakoid membranes and photosystem complexes.

• Function: Accessory pigment and photoprotectant, guarding against excessive light damage.