Question

what is the main responsibility of protein channels attached to the cell membrane? keeping cell turgidity at normal levels for homeostasis allowing specific molecules across the cell membrane extra support for the cell exterior and mechanical stress

Explanation:

Protein channels in the cell membrane are selective. They act as passageways. Their main job is to let specific molecules cross the membrane. Cell turgidity (related to water balance for homeostasis) is more about osmosis and overall water - related mechanisms (not the main role of protein channels). Extra support for the cell exterior (like in plant cells, the cell wall provides that, not protein channels).

Answer:

allowing specific molecules across the cell membrane