Question

identify the selectively permeable barrier of the cell that allows certain molecules to enter and exit the cell?

Explanation:

In cell biology, the cell membrane (plasma membrane) is known as the selectively - permeable barrier. It controls the movement of substances in and out of the cell. If we assume that in the given cell diagram (though the labels are not defined in terms of what each structure is named generally, but based on standard cell - structure knowledge):

• The cell membrane is the outer - most layer (if it's an animal cell) or just below the cell wall (if plant cell). If we assume that one of the labels (say B, but without seeing the actual standard labels for each part in the image, but going by the function) corresponds to the cell membrane.

Answer:

Assuming the label for the cell membrane is present (if we consider standard cell - part labels where the cell membrane is often one of the outer - most labeled parts in such diagrams), the answer is the structure corresponding to the cell membrane (plasma membrane). If we assume label B is the cell membrane (a common label in some basic cell diagrams where B could be the membrane), then the answer is B. But without seeing the actual definition of each label (like if in a standard diagram C is nucleus, D is nucleolus, E is endoplasmic reticulum, A is mitochondria, F is cytoplasm), if B is the cell membrane, then B.