Final answer:
The membrane's selectively permeability depends on the phospholipid bilayer and the presence of a. protein channels.
Step-by-step explanation:
The membrane's lipid bilayer structure provides the first level of control. The phospholipids are tightly packed together, and the membrane has a hydrophobic interior. This structure causes the membrane to be selectively permeable.
A membrane that has selective permeability allows only substances meeting certain criteria to pass through it unaided. In the case of the cell membrane, only relatively small, nonpolar materials can move through the lipid bilayer.
a. Protein channels embedded in the lipid bilayer also contribute to the membrane's selectively permeable nature. These proteins form channels or pores that allow specific substances, such as ions or larger polar molecules, to pass through the membrane. The protein channels can be specific for certain substances or allow a range of substances through.
So, much of the membrane's selectively permeability depends on both the phospholipid bilayer and the presence of protein channels.