A(n) is a group of tissues that work together to perform a common function.

I believe it's an organ

Explanation:

Organs have atleast two or more tissue types and preform specific sets of functions for the body.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.