Answer:
In single celled organisms surface area to volume ratio is optimum for diffusion/exchange of substances between the cell and its exterior and this rate of exchange suffices the requirement of a unicellular organism. However, in multicellular organisms the surface area to volume ratio is low, the exchange that takes place with the exterior or the environment occurs only through the body surface with the help of a specific structure/organ, example (Skin),However, this exchange does not compensate for millions of cells in a multicellular organism, which have distinct requirements based on their function
Step-by-step explanation:
i) Amoeba gets oxygen gas dissolved in surrounding water through its plasma membrane by the process of diffusion.
ii)The oxygen gas diffused inside the body is used up by amoeba. carbon dioxide gas is also liberated in the surrounding water through the same process of diffusion.