Final answer:
Facilitated diffusion allows particles to move through the plasma membrane with the help of proteins such as carrier proteins or channel proteins, without expending energy. It is suitable for ions and polar molecules opposed by the membrane's hydrophobic core.
Step-by-step explanation:
Type of Transport Involving Membrane Proteins
The type of transport that allows particles to move through the plasma cell membrane with the assistance of membrane-bound proteins is known as facilitated diffusion. In this process, materials such as ions or polar molecules, which are naturally repelled by the hydrophobic parts of the cell membrane, are able to cross the membrane thanks to the help of carrier proteins or channel proteins. Carrier proteins bind to the substance they transport, undergoing a conformational change to move the substance across the membrane. Channel proteins, on the other hand, form pores that allow specific substances to pass through without getting in direct contact with the hydrophobic core of the lipid bilayer.
Facilitated diffusion does not require energy because it operates down a concentration gradient. However, when molecules are too large for these methods, the cell may employ vesicle transport - endocytosis or exocytosis - which is an active process requiring energy.