Final answer:
Materials that can easily pass through the lipid bilayer are non-polar and lipid-soluble substances, fat-soluble vitamins, and gases like oxygen and carbon dioxide. Polar molecules and ions generally require assistance to cross the membrane due to their incompatibility with the hydrophobic core.
Step-by-step explanation:
Materials that can easily diffuse through the lipid bilayer of a plasma membrane are typically non-polar and lipid-soluble, with a low molecular weight. Substances like the fat-soluble vitamins A, D, E, and K, as well as fat-soluble drugs and hormones, can readily pass through the hydrophobic core of the membrane. Oxygen and carbon dioxide molecules also pass through by simple diffusion because they have no charge. However, polar substances and ions face difficulties because they do not integrate easily with the hydrophobic lipid core of the plasma membrane. Large polar or ionic molecules cannot easily pass through, and very small polar molecules, including water, tend to require assistance or specialized transport mechanisms to cross the membrane.