Final answer:
A jellyfish uses diffusion to exchange gases and nutrients with its surrounding environment because it lacks a circulatory system and its structure maximizes surface area for efficient exchange.
Step-by-step explanation:
A simple organism, such as a jellyfish, uses diffusion to exchange gases and nutrients with their surrounding environment. Unlike more complex organisms, the jellyfish and similar simple creatures like sponges lack a circulatory system. Instead, their body structure allows every cell to be in close proximity to the external environment. The cells are kept moist so that gases, nutrients, and wastes can quickly and efficiently be exchanged by diffusion. This process is sufficient for the jellyfish's needs due to its relatively low demand for oxygen and its body plan, which maximizes surface area for diffusion.