Carbon chains are principal features of both carbohydrates and lipids. what is the primary difference between these two types of biomolecules?

While both carbohydrates and lipids are made up of carbon, hydrogen and oxygen there are several differences:

1. Carbohydrates are chains of 2 or more carbon atoms.  These can be very lengthy (like long cellulose chains of glucose units). They have many polar OH groups (e.g. glucose - C6H6O6). Most carbohydrates are hydrophilic and are soluble in water because of their polar OH groups. They are not necessarily sugars nor are they necessarily sweet. They are also important components of DNA, RNA and ATP.

2. Lipids are more diverse in their chemistry. They generally have a polar region at one end (this end attracts water) and a large non polar hydrocarbon region that repels water. Lipids don't dissolve in water and instead clump together with their hydrocarbon regions on the interior. Lipids include oils, fatty acids, waxes, steroids and hormones.