Which Substances Can Pass Directly Through the Plasma Membrane

Question

Which substances can pass directly through the plasma membrane?
A)carbohydrate-bound
B)water soluble
C)lipid insoluble
D)iron soluble
E)lipid soluble

Accepted Answer

Only lipid-soluble substances, such as oxygen, carbon dioxide, and steroid hormones, can pass directly through the plasma membrane. Carbohydrate-bound, water-soluble, lipid-insoluble, and iron-soluble substances cannot cross the membrane without the aid of transport proteins.