The answer would be 100%. The answer cannot be 0% becausesurely algae produce food through photosynthesis. Also, it cannot be 15% and 50% because it is difficult to be really that precise. Algaes contain chlorophyll which is an essential component for producing their own food via photosynthesis. This is the only process for them to obtain their own food. Thus, 100% of algae uses photosynthesis.
