Which of the following statements most accurately describes a selectively permeable membrane?
a. Solutes are never able to cross the membrane.
b. Large molecules are always excluded from crossing the membrane.
c. Substances can only pass through the membrane with the help of either active or passive transport proteins.
d. Certain solutes move freely across the membrane by simple diffusion while others must be helped across by active or passive transport proteins; some substances are completely excluded from crossing the membrane.
Ans: d. Certain solutes move freely across the membrane by simple diffusion while others must be helped across by active or passive transport proteins; some substances are completely excluded from crossing the membrane.
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