Simple diffusion and facilitated diffusion are related in that both require protein carriers a. depend on a concentration gradient b. occur via contractions of cytoskeletal elements attached to membrane proteins c. are endergonic processes and thus require the hydrolysis of atp d. occur in eukaryotic cells but not in prokaryotic cells

A. depend on a concentration gradient

Explanation:

Simple and facilitated diffusion are the two methods of transport of substances down their concentration gradient. In both processes, substances are moved from the region of their higher concentration to that of their lower concentration. Since simple diffusion and facilitated diffusion are passive processes, there is no requirement of energy input to drive them. Both are driven by the concentration gradient of the substances only.

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