Question

plasma membrance are selectively perme

Plasma membranes are selectively permeable, or semipermeable, meaning that the membrane regulates what enters and leaves the cell. O the membrane allows all substances to enter and leave the cell. the membrane allows substances to exit the cell, but not to enter. O the membrane allows osmosis, but not movement of solutes, into or out of the cell.

Answer 1

Plasma membrane is called semipermeable membrane or selectively permeable membrane because it selectively permits only certain substances or molecules or solutes of a particular size to pass in or out of the cell i.e it acts as a barrier. Plasma membrane consist of lipid bilayer in which proteins are embedded.It has phospholipids having hydrophilic head (Polar) on the outer layer to interact with the water molecules and hydrophobic tail (Non polar) in the interior side. Some phospholipids are charged For example, Phosphatidylinositol and phosphatidylserine has negative charge.Thus, charged ions like Na,K,Cl are passed through the lipid bilayer with the help of carriers and channels like Voltage gated channels, Ligand gated channels like acetylcholine receptor for Na+ and K+ .These carriers are also called ionophores. They shield the charge of ions and thus, ions can penetrate the hydrophobic interior easily. Hydrophobic molecules like O2,CO2 , Small uncharged polar molecules like water,urea,glycerol,Large uncharged molecules like Glucose,sucrose can pass easily without the help of carriers or channels through the plasma membrane but Ions require the help of Carriers (Ionophores) to pass through the plasma membrane.