In simple animals, diffusion and active transport across cell membranes supply the cells with
and nutrients, and remove waste products.

In simple animals, diffusion and active transport across cell membranes supply the cells with  oxygen and nutrients, and remove waste products.

Explanation:

Cell membranes are permeable, and are responsible for regulating what substances can enter and how much can enter or leave at any given time. This permeability is essential for the cell to get nutrients and oxygen, eliminate waste and maintain a favorable environment, different from its environment. The diffusion and active transport processes play an important role in this