Question

Sun is the ultimate energy source for all food chains. But from where will animals who live deep down on the ocean bed and have never seen sunlight get energy?

Answer 1

Deep ocean life is usually found in the vicinity of hot vents. In these vents, hot gases boil up from volcanic vents, with a temperature of around 350^oC. The gases contain many sulphides and various minerals. When these hot gases hit the cold water, many of these minerals precipitate out of the water.
Specially adapted bacteria inhabit the regions around the hot vents and they directly convert the chemicals precipitating from the hot vents into energy by a process called chemosynthesis. In a way, these bacteria replace plants in the deep marine ecosystems.
Animals living in the vicinity of the hot vents either host the bacteria in their bodies or consume them directly. Other animals then eat these animals that directly feed on bacteria or host them in their bodies, leading to the formation of a complete food chain.