1. Chemically chlorophyll molecule consists of two parts head of tetrapyrrole the porphyrin ring and a long hydrocarbon tail called phytol attached to the porphyrin group. 

2. Both chlorophyll-a and chlorophyll-b are similar in their molecular structure, except that the methyl group (-CH) in chlorophyll-a is replaced with an aldehyde group (-CHO) in chlorophyll-b. 

3. Carotenoids are lipid compound present universally in almost all the higher plants and several microorganisms. 

4. They are usually red, orange, yellow, brown, and are associated with chlorophyll. They are of two types – the carotenes and xanthophylls. 

5. The carotenes (C₄OH₅ ) are orange red and xanthophylls contain oxygen. 

6. The light energy absorbed by the carotenoids is transferred to chlorophyll-a to be utilized in photosynthesis. 

7. All photosynthetic plants have these pigments that absorb light between the red and blue region of the spectrum. 

8. Carotenoids found mainly in higher plants, absorb primarily in the violet to blue regions of the spectrum. 

9. They not only absorb light energy and transfer it to chlorophyll but also protect the chlorophyll molecule from photo-oxidation. Xanthophylls (C₄OH₅6O₂ ) are yellow pigments found in fruits and vegetables.