Question

A cell is surrounded by a____________ that allows certain substances to pass through.

Answer 1

Cell membrane

Answer 2

A cell membrane or cell wall. A cell wall, if present, is exterior to the cell membrane. Cell walls are not found in animals and are found only rarely in protists, but are generally present in plants, bacteria, archaea, fungi, and algae. Technically, these features are part of the cell; they surround the cytoplasm and organelles. The cell itself is surrounded by other cells.
Source:
http://en.wikipedia.org/wiki/Cell_membra...
http://en.wikipedia.org/wiki/Cell_wall

Answer 3

I think its "CELL MEMBRANE"