Final answer:
Ions require special mechanisms, such as facilitated diffusion or active transport, to pass through the plasma membrane due to their charge and the nonpolar nature of the membrane's lipid core.
Step-by-step explanation:
Ions cannot passively diffuse across the plasma membrane due to their charge; instead, they need assistance through mechanisms such as facilitated diffusion or active transport. Facilitated diffusion involves the usage of transport proteins like channels or carriers that provide a pathway for ions to move down their concentration gradient without expending energy. Active transport, on the other hand, requires energy to move ions against their concentration gradient, using ATP and specific pumps or carriers.
Lipid-soluble molecules can pass through the membrane more easily, but ions and polar substances face resistance from the hydrophobic core of the plasma membrane. As a result, specific membrane proteins are required to help these charged particles and polar molecules move across, maintaining the essential balance of electrolytes and other substances within the cell.