Question

why do multicellular animals need an efficient excreatory system?
how does excreation takes place in plants?

Answer 1

multicellular organisms need and complex excretory system because it cannot be excreted by simple diffusion just think of the situation. single celled organisms excrete by simple diffusion like amoeba has no mouth and no excreting part.

and also refining blood so difficult in complex organisms because of varied and huge nutrient content.

excretion takes place in plants by leaving gums and resins which is sticky substance also used for gum.

they also produce a type of excretion by transpiration of water.

hope it helps thank you

Answer 2

The excretion process is concerned with the removal of waste products from the animal body. Because one-celled organisms are in constant contact with their environment, they do not need excretory organs. However, multicellular organisms need a mechanism to carry waste products from cells to the external environment.  

In plants, Carbon dioxide gas produced as a result of respiration is used up during photosynthesis. Thus, the waste released by both photosynthesis and respiration are used up by each other. Leaves have tiny pores called stomata and stems have pores called lenticels through which excess gaseous wastes are sent out.