Biofuels are an alternative to fossil fuels that are produced from fats derived from living organisms. One source of biofuel that is being explored more thoroughly in recent years is microalgae. It can bloom in places where salty water, excessive sun exposure, and lack of vital nutrients inhibit growth of other crops. But the higher the concentration of algae cells, the lower the ability to absorb light. In heterotrophic conditions, the algae can use sugars, organic acids, and other organic carbons as carbon sources, replacing the need for light.