Diffusion can occur across partialy permeable membranes, such as those surrounding cells. Therefore, diffusion is involved in the movement of important molecules into and out of cells. It is important for the uptake of substances needed by cells, and also the removal of waste products produced by the cells.
Answer: I think that it would be C because blooms are due to eutrophication, which means that there are high levels of phosphate in the water. Phosphate is a main ingredient in pesticides, which can run-off into rivers.