a green plant is a kind of organism & a leaf is a part of a green plant & if leaves fall out from a green plant, then those leaves are dead ->  fallen leaves are dead organism parts  if something contains a substance then the parts of that something contain that substance & dead organisms contains nutrients for decomposers ->  dead organism parts contain nutrients for decomposers  dead organism parts contain nutrients for decomposers & decomposition is when a decomposer returns nutrients from dead organisms to the soil by eating those dead organisms ->  decomposition can be when a decomposer returns nutrients from dead organism parts to the soil by eating those dead organism parts  fallen leaves are dead organism parts & decomposition can be when a decomposer returns nutrients from dead organism parts to the soil by eating those dead organism parts -> fallen leaves can be break down and become nutrients through decomposition