A plasma membrane is permeable to specific molecules that a cell needs. Transport proteins in the cell membrane allow for selective passage of specific molecules from the external environment.

This gives them a rigid structure. Supports and strengthens cell? Cell membrane Selectively permeable double layer of lipid and protein molecules? All cell types ? Fluid enclosed by the cell ...

A selectively permeable membrane allows some small substances to pass through but prevents larger substances doing the same. The cell wall is totally permeable and has no role in controlling what ...