Food chain is a linear sequence of organisms which starts from producer organisms and ends with decomposer species. Food chain follows a single path whereas food web follows multiple paths.
From the food chain, we get to know how organisms are connected with each other.
In scientific terms, a food chain is a chronological pathway or an order that shows the flow of energy from one organism to the other.
In a community which has producers, consumers, and decomposers, the energy flows in a specific pathway. But it flows from one level to the other, through different organisms.
But the advantageous thing is that, the quality of energy every increasing level receives is always better than the preceding level.
On one hand, food chain is a linear event or step wise process that takes place in the ecosystem whereas food web is interconnecting network of many such food chains. The source of energy is different for different living organism.Like, plants use the energy from sunlight to prepare food whereas animals eat plants as the source of energy.Example includes snake that eats small birds and finally is the quaternary consumers that includes larger animal like hawk that prey on sneak and many such animals that have no further predators.Now, after this when any organism dies, they are eaten by detrivours and hence decomposers present in the soil decays the complete organism thus returning the energy back to the environment. The sun is the source of all the energy on the earth. Secondary consumers are animals that eat other animals for energy. Decomposers are organisms that eat dead things for energy.Beside, this not all the energy they receive is used, in fact most part of it gets wasted.This way the chain continues by utilization of very less amount of energy on every increasing tropic level and returning most of the energy to the ecosystem.Though the process is similar, but this chain is different for water that involves phytoplankton, zooplanktons, and so on.Therefore, food chain is the transfer of energy from the source organism to the series of other organism who eats them and is also eaten by other organisms.