Answer: all of the above
Step-by-step explanation:
Membrane proteins relays the signals between the cell's internal and external environment. Transport proteins move molecules and ions across the membranes. Cell adhesion molecules allow the cells to identify each other and interact. There are two types of membrane proteins : Peripheral and Integral.Peripheral proteins have weaker and temporary connections to the membrane. Some just sit on the surface, anchored with a few ionic bonds while others might have small sections that dip into the hydrophobic section of the bilayer. Integral proteins are permanently connected to cell membrane.They are hard workers and have large sections embedded in the hydrophobic ( middle) of membrane. Transmembrane proteins are integral proteins that cross the membrane and can act as pathways for ions and molecules. Polytopic transmembrane proteins cross the membrane several times. Some are receptor proteins while others form channels.Ion movement that does not require work is called passive transport while active transport systems use work to move molecules.