What is the difference between diploid and haploid cells?

Diploid cells are characterized by containing two complete sets of chromosomes, one inherited from each parent. This means that for each chromosome in the diploid set, there is a homologous chromosome, making a total of two copies of each chromosome type. In contrast, haploid cells contain only one complete set of chromosomes, representing just one of each type without any duplicates. This fundamental difference is crucial for understanding various biological processes, particularly in the context of reproduction, where haploid gametes (sperm and eggs) unite during fertilization to form a diploid zygote, restoring the diploid number.

The reasons for the other answers not being correct include misconceptions about the definitions of diploid and haploid. For instance, the idea that diploid cells have one copy while haploid cells have two is fundamentally inaccurate because it contradicts the well-established definitions of these two terms. Similarly, the notion that diploid cells are found only in somatic cells does not take into account that diploid cells can also be found in reproductive tissues during certain stages. Understanding the distinction between these two types of cells is essential for a foundational grasp of genetics and cellular biology.