Explanation

Chlorophylls are magnesium porphyrin compounds. Chlorophyll-a ($C_{55}H_{72}O_{6}N_{4}Mg$) and chlorophyll-b ($C_{55}H_{70}O_{6}N_{4}Mg$), both consist of magnesium porphyrin head, which is hydrophilic and a phytol tail, which is lipophilic but chlorophyll-b differs from chlorophyll-a only in one of the functional groups bonded to porphyrin. Actually in chlorophyll-b, there is $–CHO$(aldehyde) group instead of $–CH_{3}$(methyl) group at the third C-atom in second pyrrole ring.