For each of the following questions about membrane transport, answer using simple diffusion, facilitated diffusion, or active transport. **note that more than one may be true for each question, and you may use an answer for multiple questions. a. which process(es) is (are) not energy-dependent? b. which process(es) require(s) a carrier protein or prote er protein or proteins? c. which process(es) can establish a concentration gradient? d. which process(es) can be saturated by a substrate?