What is the exact difference between grades of organization and symmetry? Explain with examples.

Explanation

I. Grades of organization :
(1) The grades of organization mean the way an organism has different body formation.
(2) Unicellular organisms like amoeba have a single cell in the body and hence the organization in its body is called protoplasmic grade of organization.
(3) Some organisms have only cells in their body. This is called cellular grade of organization. e.g. Poriferans.
(4) Some have tissues e.g. Coelenterates .They are said to have cell- tissue grade organization. Some have organs, they are said to have tissue-organ grade e.g. Platyhelminthes. All other higher animals have organ-system grade organization.
II. Symmetry :
(1) Symmetry on the other hand shows the base of the body formation.
(2) The symmetry can be understood by taking an imaginary cut through the animal body.
(3) Based on the symmetry there can be three types.
(4) In asymmetric animals, there is no symmetry in any plane. e.g. Amoeba.
(5) The bilateral symmetry is the one in which an imaginary axis can pass through only one median plane to divide the body into two equal halves. Most of the animals have bilateral symmetry and hence their organs are arranged in symmetric way on both the sides.
(6) The imaginary cut passing through the central axis can give more than one equal halves. The organs of such animals are arranged in a radius of an imaginary circle. e.g. Cnidarians and some echinoderms. Both grades of organization and symmetry are the bases for classifying animals into different phyla.