Why are living organisms classified?

How would the disposal of garbage, etc. affect the living organisms in the river?

Which of the following is correct : Cells of all living organisms have a nucleus.

Name the two types of chemical compounds (biomolecules) present in the cells of living organisms. Differentiate between them.

Why was the two-kingdom classification found to be insufficient for classifying all the organisms?

When we try to define 'living', we look for certain distinctive characteristics of living organisms. Mention four such features.