Gateway for ions to enter and leave a cell ...
A) hydrophobic end
B) hydrophilic end
C) protein channels
D) a, b, and c
The correct answer is D) a, b, and c, which means that all of the options (hydrophobic end, hydrophilic end, and protein channels) serve as gateways for ions to enter and leave a cell.
Let's break down each option:
A) Hydrophobic end: Cells are surrounded by a lipid bilayer composed of hydrophobic (water-repellent) fatty acid chains. While the hydrophobic core of the lipid bilayer does not allow ions to pass freely, it helps control the movement of ions by acting as a barrier.
B) Hydrophilic end: The lipid bilayer has a hydrophilic (water-attracting) head on its outer surface, which interacts with the aqueous environment outside the cell. This hydrophilic region allows the movement of charged ions such as sodium (Na+) and potassium (K+) into and out of the cell.
C) Protein channels: Protein channels are integral membrane proteins that act as selective gateways for ions to traverse the cell membrane. These channels provide a specialized pathway that allows specific ions to move down their concentration gradient, typically from an area of higher concentration to lower concentration.
In summary, the hydrophobic and hydrophilic regions of the lipid bilayer, along with the protein channels embedded in the membrane, work together to facilitate the entry and exit of ions from the cell.