Excretion in Paramecium sp. is by diffusion because

Excretion in Paramecium sp. is by diffusion because it has a large surface area to volume ratio. Paramecium is a single-celled organism that lives in aquatic environments, where it constantly takes in water and nutrients and expels waste products. Because Paramecium is small and simple, with only a few internal organs, it relies on diffusion to excrete waste products such as carbon dioxide and ammonia. Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration, and it is very efficient in small organisms like Paramecium that have a high surface area to volume ratio. This means that the organism's outer surface area is relatively large compared to its overall volume, allowing for efficient exchange of gases and other small molecules through the cell membrane.