cell membranes are selectively permeable. what does this mean?
The Cell membrane is selectively permeable because it needs to control entering and leaving. The cell needs to control what enters and leaves. It needs to keep somethings in and other things out.
anna is right
The term "selectively permeable" refers to the characteristic of a cell membrane that allows certain substances to pass through while restricting the passage of others. It means that the membrane is able to discriminate between different molecules or ions, allowing only specific ones to enter or exit the cell.
To understand how a cell membrane achieves selectively permeability, we need to consider its structure. Cell membranes are primarily composed of a phospholipid bilayer, which consists of two layers of phospholipid molecules. These molecules have a hydrophilic (water-loving) head and a hydrophobic (water-repellent) tail. The structure of the phospholipids allows them to arrange themselves in such a way that the hydrophobic tails face inward, away from the surrounding fluid, while the hydrophilic heads face outward towards the fluid.
This arrangement of phospholipids creates a barrier that prevents the free passage of water-soluble substances, such as ions and most large polar molecules, through the membrane. However, small nonpolar molecules, like oxygen and carbon dioxide, can easily pass through the hydrophobic region of the phospholipid bilayer by simple diffusion.
In addition to the phospholipids, cell membranes also contain various proteins that play a crucial role in selective permeability. These proteins are embedded within the lipid bilayer and act as channels or transporters, allowing specific molecules or ions to cross the membrane.
For example, integral membrane proteins called channel proteins form pores or channels that selectively allow certain ions, such as potassium or sodium ions, to move through the membrane. Other proteins called carrier proteins or transporters bind to specific molecules and undergo conformational changes to move substances across the membrane. These proteins provide a level of specificity in determining which molecules can pass through.
Overall, the selectively permeable nature of cell membranes is essential for maintaining the internal environment of a cell by regulating the passage of substances, allowing it to control what enters or leaves the cell and ensuring the proper functioning of biological processes.