Algae, like higher plants, obtain energy by photosynthesizing; essentially producing their food by capturing the energy form the sun. Many algae store energy in the form of starch. Other algae use other compounds and distinction between some algae groups is based upon which compound that they use to store energy. For example, Rhodophyta (red algae) store energy in the form of floridean starch, whereas the Phaeophyceae (brown algae) store their energy in the form of laminarin.

The green colour of algae derives from the dominance of chlorophyll as a photosynthetic pigment. The other colours of many algae does not mean that they lack chlorophyll but that the chlorophyll is masked. These algae have accessory photosynthetic pigments which conceal the green colour of chlorophyll. Rhodophyta contains the pigment phycobilin, giving it a red colour while the group Chrysophaceae contain the pigment fucoxanthin which gives them a golden colour.