The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
A cell is the structural and functional unit, of all organisms that serve as a building block of all organisms (both unicellular and multicellular) and is capable of carrying out all life processes. All cells are delimited by plasmalemma/cell membrane, which is a biological membrane that separates the cell’s interior from surrounding and from other cells. Being selectively permeable layer, cell membrane allows the exchange of desired molecules only thereby maintaining the unique chemical composition of cell’s interior. Thus, the correct answer is option A.