The pores of the cell membrane only allow objects of a certain size or polarity through. The lipids that make up the membrane have a certain polarity at the head and tail and only certain objects are allowed through because of this.
Technically that isn't a question, but yes. The cell's membrane is selectively permeable because it allows some chemicals and molecules to pass through (such as water), but also rejects other...
A cell membrane (the outer casing or inner casing in a plant cell) is selectively permeable. This is because some materials can pass freely through the cell membrane while others cannot.