Concept:In unicellular organisms like Paramecium, excretion occurs by simple diffusion through the body surface.Explanation:Paramecium is a single-celled organism.Its body is directly surrounded by water.A large surface area compared to its small volume allows waste products such as ammonia to pass out rapidly through the cell membrane.Thus, it does not require special excretory organs.Answer:C. it has a large surface area to volume ratio.