Best answer! Why are plasma membranes described as semipermeable?
1. The plasma membrane will allow certain substances to cross it but not others! Thats why plasma membrane is referred to as “selective permeable” (or “semipermeable”). The plasma membrane’s permeability depends on a large part on its makeup. Both the protein portion and the phospholipid portion of the membrane are involved in the permeability 2. Molecules that pass through the phospholipid bilayer easily… Hydrophobic molecules (oil soluble) – O2, N2 Nonpolar – benzene Small uncharged polar molecules – H2O, Urea, glycerol, CO2 Molecules that don’t pass through the phospholipid bilayer easily… Large uncharged – Glucose Polar molecules – Sucrose Ions (charged) – H+ , Na+ , HCO3 , K+Ca2+ , Cl- , Mg2+ So we can conclude that Permeability is because of the presence of the membrane proteins. with following characteristics.
