Question

.In single celled organisms diffusion is sufficient to meet all their requirements of food, exchange of gases or removal of wastes but it is not in case of multicellular organisms. Explain the reason for this difference.​

Answer 1

Unicellular organisms can absorb sufficient oxygen because of its complete contact with the atmosphere, but in multicellular organisms the rate of absorption and diffusion becomes very less because all cells are not in direct contact with the atmosphere. Multicellular organisms require greater amount of oxygen to sustain life processes which cannot be fulfilled by the process of diffusion.

Answer 2

Bcoz as we move higher i.e from simple unicellular organisms to multicellular
the body structure becomes complex and so does thenfunctions of various organs.And in that case simple diffusion can't meet the large requirements may be it with the food or gaseous exchange or removal of wastes.A developed system is needed for a different function as the complexity in structure increases.