Correct Answer - A
Unicellular organisms such as Amoeba, Paramecium have some organelles These are freshwater animals i.e., they live in hypotonic solution. Therefore, water flows from outside to inside of the body of the organism.
The contractile vacuoles in these organisms collect this excess water and gradually increase in size. When the vacuoles reach a critical size they contract, squeezing out their contents through the process of simple diffusion.
