Final answer:
The cell membrane is sometimes permeable to K+ (potassium ions) due to the presence of channel proteins. Its permeability can change in response to cellular processes, and it is crucial for maintaining the specific internal environment of a cell.
Step-by-step explanation:
The cell membrane is highly specialized in its permeability and is sometimes permeable to K+ (potassium ions). However, it is normally impermeable to other ions such as Na+ (sodium ions). Membranes are permeable to K+ primarily due to channel proteins that selectively allow these ions to pass through. For example, during the resting potential of a neuron, the membrane is permeable to K+ through potassium channels that are always open, which contributes to the maintenance of the cell's resting potential.
The concept of diffusion also affects the permeability of the membrane with respect to K+. Ions move from areas of higher concentration to lower concentration until an equilibrium is reached where the Coulomb force, which is the electrostatic force between charged particles, balances the diffusion. However, despite this natural diffusion process, ions cannot pass through the cell membrane without assistance due to the hydrophobic core of the phospholipid bilayer. The transfer of K+ through the membrane is facilitated by membrane transport proteins such as channel proteins.
The selective permeability of the cell membrane is a key concept in biology because it allows the cell to maintain a specific internal environment. Thus, while cell membranes are sometimes permeable to K+ via channels and transport mechanisms, they are not always so, and their permeability can change in response to various cellular processes, including the action potential in neurons where permeability to different ions fluctuates rapidly.