Final answer:
A haploid cell contains one set of chromosomes, distinguishing it from a diploid cell, which has two sets. Haploidy is critical for sexual reproduction, ensuring that gametes (sperm and egg) have half the typical chromosome number before fertilization.
Step-by-step explanation:
The question pertains to the number of chromosome sets in a haploid cell. A cell that is haploid contains one set of chromosomes. This is in contrast to a diploid cell, which contains two sets of chromosomes (notated as 2n). In sexual reproduction, haploid cells, such as sperm and egg, combine to form a diploid zygote with half the DNA from each parent, thus maintaining the species-specific chromosome number.
Diploid cells can become haploid through meiosis, a two-stage division process that results in four haploid daughter cells from one diploid parent cell. The first meiotic division produces two haploid cells with one chromosome set each, and the second division separates sister chromatids without further replication of DNA, ensuring that the gametes produced will have only one copy of each chromosome.