"Good point (I think). Actually, I'd not encountered the term 'biomolecule'
before."
It's commonly used among biochemists as a substitute for "biochemical",
especially if what is being refered to is a macromolecule like a protein,
starch or DNA. Both terms literally mean "chemical (or molecule) of life",
hence my definition of "chemicals or molecules used exclusively in
biological systems."
"How does that differ from an 'organic' molecule?"
An "organic" molecule is any that contain carbon, but generally it is
reserved for alkanes, alcohols, esters, ethers, carboxylic acids,
hydrocarbons and other aliphatics, and aromatics like benzene, to name a
few. Technically, carbonates and bicarbonates are also "organic" molecules,
but they are generally counted as inorganic.
Kevin L. O'Brien