The microorganisms without which animals and plants would not live are called decomposers.

Here's why:

* Decomposers break down dead organic matter: This includes dead plants, animals, and waste products.

* They release nutrients back into the environment: These nutrients, like nitrogen and phosphorus, are essential for the growth of new plants.

* They form the base of the food chain: Many small organisms, like insects and worms, feed on decomposers, which then become food for larger animals.

Without decomposers, dead organic matter would pile up, nutrients would become trapped, and the entire ecosystem would collapse.