Which statement best describes the function that results from the selectively permeable nature of a plasma membrane?
a.
instructions given by a cell nucleus can move throughout the cell more easily.
b.
all substances can easily travel across the membrane, so the cell does not need to expend energy transporting them.
c.
the cell is hard and durable because the membrane does not allow any outside substances to enter the cell.
d.
some substances are permitted to move into and out of the cell, while other substances are not.

The answer I think is D. Selectively describes the way in which things is "selected", some may of may not be selected. Permeable refers to whether something is allowed or can go through the "plasma membrane" in this example. Thus, D is the answer that corresponds most strongly to this question, whereas the others do not. A and B mention how substances can "easily" move through across the membrane while C states the opposite in that other substances cannot enter it at all. This does not fit with the question in which it asks for the function of a "selectively permeable" plasma membrane, where substances are EITHER OR NOT selected to be ALLOWED INTO it.  

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