Question

in all sexually reproducing organisms, the diploid phase of the life cycle begins at
○ mitosis.
○ gamete formation.
○ fertilization.
○ spore formation
○ meiosis.

Explanation:

Diploid cells have two sets of chromosomes. In sexual reproduction, haploid gametes (each with one set of chromosomes) fuse during fertilization, creating a diploid zygote, which starts the diploid phase of the life cycle. Mitosis, gamete formation, spore formation, and meiosis are either part of the diploid phase or produce haploid cells, not starting the diploid phase.

Answer:

fertilization.