What prevents ions from crossing the plasma membrane via simple diffusion?
A. Ions are too large.
B. Ions carry a charge.
C. Ions are hydrophobic.
D. Ions do not produce a concentration difference.
E. Ions cannot interact with membrane-bound proteins.
Answer (2)
Simple diffusion is the concept of a substance moving from an area of high concentration to a lower concentration without energy input. Because the plasma membrane is made of lipids which are non-polar, this membrane readily allows non-polar substances to diffuse through easily. If a substance has a charge like that of an ion, it will be difficult for the ion to cross the plasma membrane through simple diffusion. The answer should be B.
Ions cannot cross the plasma membrane via simple diffusion because they are charged, which makes it difficult for them to pass through the hydrophobic interior of the membrane. Therefore, they require specialized transport mechanisms to facilitate their movement. The correct answer is B: Ions carry a charge.
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