Final answer:
Lipids, including triglycerides and phospholipids, do not have a monomer. They are composed of different types of molecules, notably fatty acids, and are characterized by their hydrophobic nature and insolubility in water.
Step-by-step explanation:
Lipids are a diverse group of macromolecules that are not formed by monomeric units in the way that proteins or carbohydrates are. Lipids do not have a monomer; instead, they are comprised of various types of molecules, often fatty acids, that contribute to the structure of complex lipids like fats, oils, and phospholipids.
Fatty acids themselves are not monomers but rather long chains of hydrocarbons with a carboxylic acid group at one end, and they can be categorized as saturated or unsaturated based on their bond structure. Triglycerides, a type of fat, are made up of three fatty acid chains attached to a glycerol molecule, but still, they do not have a repeating monomer unit.
Within the scope of biological membranes, phospholipids play a crucial role, consisting of two fatty acids, a phosphate group, and a glycerol or sphingosine backbone. These structures are not uniform or repeating units, which means they do not qualify as monomers.
Lipids are characterized by their hydrophobic, or water-repellent, nature which is due mainly to their long hydrocarbon chains. Because lipids are insoluble in water but soluble in nonpolar solvents such as ether or chloroform, they have critical roles in cellular structures like membranes, as well as in energy storage and signaling within organisms.