Concept:Small organisms rely on diffusion for transport because of their large surface area relative to volume.Explanation:In mammals, the body is large and complex, so diffusion alone is too slow to transport oxygen, nutrients, and waste to all cells. A circulatory system is needed.Amoeba is a single-celled organism with a large surface area-to-volume ratio.Diffusion is sufficient to transport materials directly across its cell membrane.Answer:B. Diffusion is sufficient to transport materials in Amoeba