The so-called non-utilization means that it cannot be used as the source of synthetic organic matter. Usually they synthesize inorganic substances, carbon dioxide, ammonia, etc., and then use these organic substances for metabolic activities.

Autotrophic organisms need to breathe to provide energy, and organic matter is degraded during breathing, so they need to breathe and organic matter, but the organic matter here is generally not external organic matter.

The growth of green plants with urea is accelerated because microorganisms in the soil degrade urea into ammonium ions, which are absorbed by plants instead of directly.