Question

Which organisms are called primitive and how are they different from so called advanced organisms?

Answer 1

Advanced organisms were once primitive. These have evolved according to the situation and developed advanced features to survive in the environment.

Complete answer:
Primitive organisms are those whose body has not changed much since ancient times. Where advanced organisms have developed according to the situation.
Features of primitive organism:
1. They exhibit small bodies and simple organization of bodies.
2. They are found in the first few ladders of evolutionary scale. Whereas advanced organisms are found on the top of the evolutionary scale.
3. Advanced organisms have developed from them by changing their body according to the need.
4. They may be prokaryotes or single-celled organisms.
5. Primitive organisms are considered as “lower organisms” and advanced organisms are called “higher animals”.
6. Movement by flagella or cilia in primitive organisms whereas in advanced organisms they have limbs, fins, pods to move.
7. The body is simple and diploblastic whereas advanced organisms are triploblastic (endoderm, ectoderm and mesoderm).
8. Primitive organisms have an open blood circulatory system where organs float in the blood. Some of them have hemocoel fluid or some have no blood.
9. Organ development is also not observed in primitive organisms.

Note:
Humans are considered as advanced organisms whereas prokaryotic organisms are considered as primitive organisms.