While the majority of the energy within an ecosystem is done through photosynthesis, it is not the only way that energy is processed. What about ecosystems that exist where sunlight is not available? How do they survive?

The next page will discuss chemosynthesis, which is like photosynthesis, but different in some important ways. Chemosynthesis also makes glucose, like photosynthesis, but it uses chemicals like hydrogen sulfide rather than the sun as its energy source.

After that page there will be two videos that show alternative ways in which energy is introduced within an ecosystem. The first video is about coral reefs, in particular the Great Barrier Reef in Australia. Following that video, there is another video on hydrothermal vents.