Question

why the viruses are not classified in to other four organism as bacteria , fungi ,protozoa ,algea

Answer 1

Virus is a very diffrent organism. It only consist of head and body part which are of only proteins. It doesn't consist of cells. Though they show presence of RNA but It can't said to be living or non living. Because, it is living while in livings .( as it uses human machinery for its life) . and non living while out of living body. So characteristics of a virus doesnt match with the any kindom of livings.that is why..it is not included in any kindom. It is said to be in threshold of life.

Answer 2

Viruses infect both eukaryotes and prokaryotes. Viruses reproduce inside a living organism. They can develop only inside the cells of the host organisms (which may be an animal, plant or bacterium).
Thus, as long as viruses are outside the living cells, they behave as non-living things.