A food chain is a simplification within an ecosystem and depicts the flow of food and energy through a series of organisms (including plants). A food web is a series of interconnected food chains representing the flow of food and energy from one trophic level to the next. 

Similarities:

Both the food chain and food web represent flow of food and energy through various organisms (including plants) and point from the producers to the consumers. Both the food web and food chain include a number of organisms including both producers and consumers (as well as decomposers). 

Differences:

A food chain is very simple, while a food web is very complex and consists of a number of food chains. In a food chain, each organism has only one consumer or producer. For example, a deer eats grass and a tiger eat the deer. In a food web, a consumer may eat a number of different producers. Isolated food chains are not very good for an ecosystem and induce instability, while a food web increases the stability of the ecosystem. 

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