Detritus food chain and grazing food chain are two types of food chains.All the organisms die and get decomposed. Where as not all organisms are eaten by others. There are number of organisms which feed on others but do not get fed by any other organism .So all such organisms also die and be a part of detritus food chain.Every living organism, if not eaten by others, will be part of DFC.That is why more matter and more energy flows in DFC than in GFC.