Final answer:
Under a microscope, whitefish blastula cells are studied to identify stages of the cell cycle such as metaphase and cytokinesis. The frequency of these stages can be used to estimate the time cells spend in each phase. This process demonstrates the critical role of mitosis from zygote to blastula.
Step-by-step explanation:
Whitefish blastula cells observed under a microscope can be in various stages of the cell cycle, including interphase and the mitotic stages which are metaphase and cytokinesis. Metaphase is characterized by chromosomes aligning at the cell's equatorial plate, visible with a high-power objective lens. Cytokinesis is the stage where the cytoplasm of the parent cell fully divides, creating two daughter cells, often indicated by the formation of a cleavage furrow visible under the microscope.
By examining a prepared microscope slide of a whitefish blastula cross-section, a student can practice identifying these stages. The number of cells in each mitotic stage provides an estimate for the time taken by cells to complete that stage, which can be calculated by multiplying the observed frequency of a stage by 24 hours. This exercise underscores the importance of mitosis in the development of multicellular organisms, beginning from a single-celled zygote through a series of rapid cell divisions known as cleavage, leading to the formation of the blastula.