What is simple diffusion?

Facilitated diffusion is the process of spontaneous passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins

Explanation:

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the movement of molecules through a cell membrane without using a channels formed by intergal membrane protein is called simple diffusion

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.