What is the difference between diploid and haploid cells?

diploid cells contain two chromosomes while haploid cells contain one.
diploid cells are usually gametes.
diploid cells have paired chromosomes while haploid cells have single chromosomes.
there is no difference.

Diploid cells contain two complete sets (2n) of chromosomes. Haploid cells have half the number of chromosomes (n) as diploid - i.e. a haploid cell contains only one complete set of chromosomes. Diploid cells reproduce by mitosis making daughter cells that are exact replicas.

thermophiles, notice the prefix thermo.

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.