Final answer:
Passive transport across a plasma membrane can occur with the help of specific carrier proteins through a process called facilitated diffusion. These carrier proteins are selective and play a crucial role in maintaining the cell's overall selectivity.
Step-by-step explanation:
Passive transport across a plasma membrane can occur with the help of specific carrier proteins. These carrier proteins bind to ions or molecules on one side of the membrane, change shape, and then transport the bound molecules across the membrane to the other side. This process is known as facilitated diffusion and is a type of passive transport.
Carrier proteins are selective, meaning they only allow specific types of molecules to cross the membrane. They play a crucial role in maintaining the cell's overall selectivity and functioning properly. Carrier proteins are involved in various physiological processes in the body, such as the transmission of nerve messages.