Final answer:
The pouchlike structure that joins the ileum at the ileocecal valve is the b) cecum. The appendix, or vermiform appendix, is attached to the cecum and may have roles in immunity and maintaining gut flora.
Step-by-step explanation:
The Pouchlike Structure in the Digestive System
The pouchlike structure that joins the ileum at the ileocecal valve is the cecum. The cecum is a sac-like part of the large intestine located below the ileocecal valve. It plays a role in absorbing water and salts from the contents that transition from the small intestine. The appendix, or vermiform appendix, is a small, tube-like structure that attaches to the cecum. While the appendix's precise function in humans remains a topic of research, it contains lymphoid tissue, supporting a role in immunity, and may serve as a reservoir of bacteria, repopulating the gut flora after diarrheal illnesses.
The appendix is often mistakenly thought to have no significant function. However, recent studies suggest that this vermiform appendix may have an immunologic role and contribute to maintaining gut health. Though sometimes considered vestigial, the appendix is integrated into the lymphatic system of the gut.