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Mention the functions of carotenoids.


Functions of Carotenoids :

1. Carotenoids function as accessory pigments. They absorb radiant energy in the mid region of visible spectrum.

2. They protect the chloroplast constituents from nascent oxygen released during photolysis of water.

3. Carotenoids provide colour to the flowers and fruits that help in pollination and dispersal.

 

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 What are the steps common to C3 and C4 cycle ?

Steps common to C3 and C4 cycle are :

1. Photolysis of water in light reaction is common to both C3 and C4 cycle.

2. In both, dark reaction occurs in stroma region of chloroplast.

3. Calvin cycle results in the formation of starch in both the types of plants.

4. Both undergo phases of carboxylation and regeneration of RUBP during dark reaction.

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Write a note on phycobilins.

Phycobilins are water-soluble pigments found in the stroma of chloroplast organelles that are present only in Cyanobacteria and Rhodophyta. The two classes of phycobilins include phycocyanin and phycoerythrin. Phycocyanin is a bluish pigment found in primarily cyanobacteria (blue-green algae) to aid in absorption of light in photosynthesis, while  phycoerythrin is a pigment found in Rhodopyta (red algae) that is responsible for its characteristic red color. It is an accessory pigment that allows red algae to carry out photosynthesis in deep water where wavelengths of blue light are most abundant by absorbing blue light and reflecting red light.

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What is the abvantage of having more than one pigment molecule in a photocentre ?

The advantages of having more than one pigment are:

(1) To efficiently capture sunlight and to facilitate reaction.

(2) These additional pigments protect chlorophyll molecule from nascent oxygen.

(4) Some pigments act as co-enzymes which are used for some metabolic activities of chloroplasts.

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Why does rate of photosynthesis in plants growing under the forest canopy show marked decrease ?

Rate of photosynthesis in plants growing under the forest canopy shows marked decrease because when the light passes through a forest canopy, there is a preferential absorption of blue and red regions of visible lights by the foliage of the trees, thereby reducing the visible light absorption in the plants growing under the forest canopy. Thus, there is a marked decrease in the rate of photosynthesis.
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