Question

which is true about mediated transport of substances across cell membranes? multiple choice it involves a specific membrane protein that functions as a carrier molecule. it always involves the movement of substances against a concentration gradient. it is always directly coupled to the splitting of atp molecules. there is no limit to how fast it can occur as the concentration gradient becomes larger. it is the main mechanism for transporting hydrophobic molecules across membranes.

Explanation:

Mediated transport across cell - membranes involves specific membrane proteins (transporters or carriers) that assist in moving substances across the membrane. Facilitated diffusion (a type of mediated transport) can occur down a concentration gradient and is not always coupled to ATP hydrolysis. Also, there are limits to the rate of transport due to the number of carrier proteins. Hydrophobic molecules can cross membranes by simple diffusion rather than being the main role of mediated transport.

Answer:

It involves a specific membrane protein that functions as a carrier molecule.