Question

Why is diffusion insufficient for exchange of gases in higher organism?

Answer 1

because they have high Kinetic energy

Answer 2

In single celled organism no specific organism is needed for taking in food, exchange of gases or removal of waste because the entire body of the organism is in contact with the environment. But in case of multi cellular organisms, body size becomes bigger and body design becomes more complex . All cells are not in direct contact with the surrounding environment . Thus simple diffusion is insufficient to meet the requirements of the cell