Final answer:
Gastrulation is the process during embryonic development where three germ layers, including the mesoderm, are generated. These layers differentiate to form various tissues and organ systems.
Step-by-step explanation:
During gastrulation, a process that occurs after the formation of the blastula, the cells in the blastula rearrange themselves to form three distinct layers.
These layers are known as germ layers. Specifically, gastrulation is characterized by the generation of the three primary germ layers: the ectoderm, mesoderm, and endoderm. Each of these germ layers will eventually give rise to different tissues and organ systems in the developing embryo. For instance, the ectoderm develops into the nervous system and skin, the mesoderm into muscle cells and connective tissue, and the endoderm into various internal organs.
Therefore, the correct answer to the student's question, "Which of the following is something that occurs during gastrulation?", is option (c) 3 germ layers including mesoderm are generated.