Question

State the various levels of organisation found in the animal kingdom.

Answer 1

Animals have different organization levels which begins from a single cell to a whole individual organism. This level of organization helps in classification of animals in various categories.

Complete answer:
Let us discuss the various levels of organization in the animal kingdom.
Cellular level of organization: This level of organization determines whether the organism is unicellular or multicellular in organization. Those organisms having a single cell are termed unicellular while those having multiple cells are called multicellular.
Tissue level organization: Cell combines to form tissue. In tissue level organization, organisms have a group of cells forming tissue that is responsible for specific activities. For example, metabolic activities in coelenterates.
Organ level of organisation: Tissue forms the organs which are specialised to perform specific functions. Example- Platyhelminthes
Organ system level of organization: In this complex organ systems are involved to perform various functions. Examples- mollusks and chordates

Animals are also divided based on their symmetry. Some animals like sponges are asymmetrical and cannot be divided into two equal halves. Echinoderms and coelenterates have radial symmetry in which any plane that passes through the central axis divides the body into two equal halves. Annelids and arthropods have bilateral symmetry in which they can be divided into two equal halves only through a single plane.
Animals are also classified on the basis of diploblastic and triploblastic organization in which diploblastic (coelenterates) are those that have two germinal layers ectoderm and endoderm while triploblastic (platyhelminthes to chordates) have three germinal layers called ectoderm, mesoderm and endoderm.

Note: Animals are also divided on the basis of coelom, segmentation and presence of notochord. Based on these criteria different animals are classified into different categories of organization.