And so this favors membrane fluidity, it decreases the rigidity and lowers the melting temperature of that system. So we see that increasing the length of our fatty acid chains and removing those says double bonds basically makes the membrane more rigid and increases the melting temperature of that membrane. Now, in bacterial cells, bacterial cells tend to basically use these two factors to control and regulate the rigidity or fluidity of the membrane. So they usually increase the number or decrease the number of these double bonds. Now, in animal cells, we normally use cholesterol. So let's see how cholesterol can be used to basically regulate the rigidity of the membrane.