Suppose you are a bacterium growing happily at 25 o C. Suddenly, a scientist moves you into a 37 o C environment. Fluidity will increase because temperature increases the motion of the phospholipd tails. Fluidity can be reduced by changing the composition of phospholipids. Increasing the proportion of saturated fatty acids or cholesterol would work. Long chain fatty acids can assume innumerable conformations by rotation about the single C-C bonds.
Soaps are sodium or potassium salts of long chain fatty acids.
They readily form micelles in water, and this is the basis of their cleansing action. Explain why this happens. Protonation eliminates the negative charge on the acidic end of the molecule. Thus, the extremely strong preference of one end of the molecule for water rather than itself disappears, and the fatty acids associate with one another in a uniform manner, rather than as micelles separated by water. Phospholipase is an enzyme that cleaves phospholipids.