What term describes a cell that has only one set of unpaired chromosomes?

The term that describes a cell with only one set of unpaired chromosomes is "haploid." In a haploid cell, the chromosome number is denoted as n, which represents one complete set of chromosomes. This is characteristic of germ cells, such as sperm and egg cells in animals, where each gamete carries just one set of chromosomes, ensuring that when fertilization occurs, the resulting zygote will have the correct diploid number of chromosomes, which is two sets (one from each parent).

The concept of haploidy is significant in the context of sexual reproduction, where haploid cells combine during fertilization to restore the diploid state in the new organism. This reduction in chromosome number during gamete formation is also a critical aspect of meiosis.

In contrast, diploid cells contain two sets of chromosomes (2n), polyploid cells have more than two sets (such as triploid or tetraploid), and the term monoploid typically refers to a condition similar to haploid, but often emphasizes specific instances or taxa in academic discussions. The unique identification of haploid cells is fundamental in the study of genetics and biological inheritance.