What is the most important distinction between the membrane transporters known as channel proteins and those known as carrier proteins?

Channel proteins form hydrophilic channels to passively transport substances down the concentration gradient.

Carrier proteins bind to substances to transport them actively against the concentration gradient. They do not form channels.

Explanation:

Channel proteins are the membrane proteins that serve in transport of small polar molecules and/or ions by making a hydrophilic pore across the membrane. These molecules diffusion through the pore and exhibit facilitated diffusion.  

Carrier proteins are the membrane proteins that transport the substances across the membrane by binding to them. They do not form the hydrophilic channels. Carrier proteins serve in the active transport of molecules against the concentration gradient.

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