Most algae gain fuel through the process of photosynthesis, and green algae is no exception. In fact, according to Encyclopedia Britannica, most of what is known about photosynthesis actually comes from studying green algae.
Even though green algae prefers using photosynthesis, there is a type of green algae that can break down and eat plant materials. Live Science explains that it is the first plant known to use the cellulose from other plants as a source of food. This cannibalization occurred when the algae was deprived of carbon dioxide, which algae turns into food, along with water, by using the sun as an energy source.