Question

which organisms are called primitive and how are they different from the so called advanced organisms

Answer 1

On the basis of genetics, the organism that has more number of chromosomes (DNA) is more advanced

The primitive ones are usually smaller organisms

Answer 2

An advanced organism or higher organism has a complex body structure and organization. For example, an Amoeba is more primitive as compared to a starfish. Amoeba has a simple body structure and primitive features as compared to a starfish. Hence, an Amoeba is considered more primitive than a starfish.