Conversation so far:
where does diffusion occur in the excretory system
In the excretory system, diffusion of water, salts, and waste products occurs in the kidneys. Diffusion of calcium from food into cells occurs in the intestines.
what are some advantages of diffusion in the body
The advantage of diffusion is that it does not require as much energy to regulate, as opposed to a cell having to make proteins that pump molecules across a membrane.

Question: what else uses this process
Self-contained rewrite: what else in the body besides the excretory system uses diffusion