What is the purpose of the plasma membrane?

encloses specific structures

reproduces cells

makes food for the cell

keeps the cell small

The primary function of the plasma membrane is to protect the cell from its surroundings. Composed of a phospholipid bilayer with embedded proteins, the plasma membrane is selectively permeable to ions and organic molecules and regulates the movement of substances in and out of cells.

Explanation: hope this helped

this is not my best subject but I believe its A..

Explanation:

Its job is to protect the cell from its surrounding environment

an angle + its complement = 90 degrees

answer is  

loa ≅ lma

to prove that the triangles are congruent using the aas congruence