Most people do not realize that the lack of a gene can often result in a trait, such as the inability to digest milk because the cell doesn't express a gene that codes for the enzyme lactase. The failure of which biomolecule results in the missing gene that leads to the inability to digest milk?

I would say protein.

Explanation:

Enzymes (protein) are responsible for proofreading the replicated DNA sequences and fixing any mistake. The failure of that, brought about this genetic fault that gets passed down generations.

the way that the mass of carbon can be conserved through cellular respiration is through a process/law called the law of conservation of mass which even tho it undergoes a process, mass is not be destroyed or changed

coal is not sustainable because it will one day run out.