$(a)$ What makes the biosphere a stable system?
$(b)$ What happens when the components of the biosphere interact with each other?

(N/A) The biosphere is a stable system due to the constant and balanced interaction between its biotic (living) and abiotic (non-living) components,which maintains a state of dynamic equilibrium.
$(b)$ When the components of the biosphere interact,there is a continuous transfer of matter (nutrients) and energy between them,which supports life processes and maintains the balance of the ecosystem.