Here's why:

* Decomposers break down dead organic matter. Bean plants are living organisms and produce their own food through photosynthesis.

* Bean plants are producers. They are part of the food chain, providing energy for herbivores that eat them.

Decomposers are organisms like fungi and bacteria that break down dead plants and animals, returning nutrients to the soil. While a bean plant might eventually decompose after it dies, it is not a decomposer while it is alive.