1.Supporting and retaining the cytoplasm (inner cell) and help shape of many organelles within the cell, e.g., mitochondria, ER, Golgi complexes, secretary granules, lysosomes and nuclear membranes.

2. They have selective permeability for:
nutrients inand waste products out.
non-polar molecules and some small polar molecules can cross.
Most polar compounds, e.g. amino acids, must be specifically transported across the membrane by proteins (Transport).

3. Plasma membranes plays roles in cell-cell interactions and transmembrane signaling (e.g. starvation, rise of glucose level).

4-They provide e sites of energies transduction such as photosynthesis and Phosphorylationoxidation