A standardized method of classification of living things helps taxonomist make fewer mistakes. With a systematic classification system, they look at more characteristics to determine what animals belong to a particular species.
This question is vague therefore I have provided two answers and explanations. The single cell is the smallest living unit within a living system. Quarks are the smallest particles of matter and atoms which composes all living things.
Classification means to put things into groups according to their characteristics. Living organisms are arranged in different groups due to their similarities and differences. This grouping is called CLASSIFICATION.