membrane. The only exit is through an enzyme complex, which uses the energy to
esterify adenosine diphosphate (ADP) with additional phosphate ions to generate ATP.
ATP is the principal, diffusible energetic molecule in cells. Along with NADPH, it is
used to drive biosyntheses.
Fig. 2.18 Chemical structures of some abundant phytoplankton pigments: (a)
Chlorophylls-a and b. (b) β-carotene, the most common carotenoid, and five
xanthophyll derivatives. The R side chains for 19′ butanyloxyfucoxanthin and 19′-
hexanyloxyfucoxanthin are: respectively. (c) Several
versions of phycoerythrin-like pigments based on open pyrrole structures.