Which part of the cell is selectively permeable?
The parts of the Cell that consist of a phospho-lipid bi-layer are selectively permeable. The reason it is selectively permeable is that it is made up two layers of phospho-lipids, with the hydrophobic fatty acid tails together and the hydrophilic heads facing out. This allows uncharged small molecules like O2 and CO2 to freely diffuse through it. This is so that ion gradients can be maintained across it.
