Algae can either be autotrophic or heterotrophic in nature. Most of them are photoautotrophic i.e. they need only light and Carbon Dioxide as their chief source of energy and carbon. Chemoheterotrophic algae require other external organic compounds as carbon and energy sources
Reserved food materials present in algae include Starch, Oils, Floridean starch, Laminarin, Paramylon, soluble carbohydrates and Chrysolaminarin.