Hydrogens are compounds or structures composed of carbon and hydrogen only. Hydrocarbons exist in two forms; saturated and unsaturated. The saturated form contains only single bonds (two electrons shared) whereas the unsaturated form contains at least one carbon to carbon double bond (four eletrons shared).
Hydrocarbons can be found in biological molecules such as phospholipids, steroids (hormones and chloesterol) and fats such as triglycerides (located in the fatty acid chain). It is due to the nature of the hydrocarbons that lipids are hydrophobic. 
- ↑ Letts and Lonsdale, Revise AS Chemistry
- ↑ http://telstar.ote.cmu.edu/biology/MembranePage/index2.html