Since water is the major liquid within all living organisms (i.e., approximately
70% of the human body mass is water), one might expect that most chemical
components in cells would be polar substances that are readily soluble in
water. This is generally the case, however there exists a rather heterogenous
group of biomolecules that are non-polar and totally (or nearly) insoluble in
water. Such biomolecules are termed “lipids”.