What type of organism is the basis of the food chain?

So-called 'primary producers', organisms that produce biomass from simple chemical compounds and an external energy source. Plants are primary producers: they produce plant biomass from CO2 and water, using the sunlight as a source of energy. In the ocean, phytoplankton is responsible for most of the primary production. Some organisms use energy sources other than light to produce biomass. Some bacteria, for instance, derive their energy from the oxidation of inorganic chemical compounds (e.g. H2S). In the deep sea, whole communities are supported by this kind of chemosynthesis.