What does alternation between haploid and diploid generations refer to?

• A. A life cycle with only haploid phase
• B. A life cycle with only diploid phase
• C. Asexual reproduction without gametes
• D. Alternation between haploid cells and diploid cells

Answer: (D)

Alternation of generations describes a life cycle that includes two multicellular stages with different chromosome numbers, shifting between haploid and diploid forms. The best description says the cycle alternates between haploid cells and diploid cells. In many plants and some algae, the haploid generation (gametophyte) produces haploid gametes, which fuse to form a diploid zygote that grows into the diploid generation (sporophyte). The diploid sporophyte then produces haploid spores by meiosis, starting the cycle again. The other ideas describe life cycles that stay in one ploidy level or reproduce asexually, which don’t capture this alternating pattern.