Final answer:
The process that can occur through meiosis but not mitosis is C) Diploid cells form haploid cells. Meiosis specifically reduces the number of chromosomes to create haploid cells for sexual reproduction, while mitosis creates genetically identical cells to the parent.
Step-by-step explanation:
The process capable of occurring by meiosis but not mitosis is the formation of haploid cells from diploid cells. During the sexual reproduction cycle, diploid organisms utilize meiosis to produce haploid cells such as sperm and eggs. These haploid cells carry half the number of chromosomes compared to the parent cell and can fuse during fertilization to create a diploid zygote. Unlike meiosis, mitosis results in the production of genetically identical daughter cells that maintain the same ploidy as the parent cell, which means haploid cells cannot be formed from diploid cells through mitosis.
Therefore, the correct answer to the student's question "Which of the following can occur by the process of meiosis but not mitosis?" is C) Diploid cells form haploid cells.