Answer:
The phospholipid bilayer describes a structure with polar heads on the outside and non-polar tails on the inside (option a).
Explanation:
The plasmatic membranes of the cells behave as a semi-permeable barrier to the passage of substances, a characteristic that depends on the hydrophobic properties of its phospholipid bilayer.
Lipidic bilayers are formed by the union of phospholipids with a hydrophobic —non-polar— head and a hydrophilic or polar tail, so they are called amphiphilic.
The bilayer phospholipids are arranged keeping the head —with a phosphate molecule— on the outside while the hydrophobic tails, formed by a double chain of fatty acids, on the inside.
The other options are not correct due to the explanation above: