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Plasma membranes are described as selectively permeable, which means they:
ALet every substance pass through freely
BLet some substances pass but not others
CBlock absolutely every substance equally
DLet only water pass and nothing besides
Answer & Solution
Correct answer: B. Let some substances pass but not others
1. A membrane that let everything through would not define a cell at all.
2. A membrane that let nothing through would starve it.
3. Plasma membranes are selectively permeable, that is semipermeable: they allow some substances to pass through, but not others.
4. Water is one of the substances that crosses, but it is not the only one.
_Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_
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