Energy

Until a few years ago it was thought that the sun supplied energy for all life.  Researchers have discovered, however, that certain microscopic organisms do not get their energy from the sun but obtain it from inorganic sources.  Perabacterium spelei, for example, derives its energy from iron carbonate (FeCO₂)  which is plentiful in its physical environment-limestone caves.  Life a green plant, it uses inorganic matter (carbon from the mineral and nitrogen from the air) to produce its food, Niphargus, a tiny, blind crustacean, consumes this organic food and is, in turn, eaten by larger animals.  Al this takes place where chlorophyll-bearing plants do not exist and where sunlight never reaches. P. spelei is, therefore the first link in this particular food chain.

Food chains, as you already know, being with producers.  Produces need certain materials and a source of energy in order to manufacture food.  In some instances, the source of energy is the inorganic matter used by the organism.  In most instances, however, the source of energy is the sun.  In fact, the sun has supplied the energy for almost all life since life began on this earth.  Its role and its great importance shall always be emphasized.