Test: Animal Kingdom - September 23, 2022 - NEET MCQ

Levels of organization, symmetry, arrangement of cells in embryo, presence of coelom, segmentation and presence of notochord are the basis for the classification in Animalia. Since all the animals are heterotrophic, there is no need to classify Animalia based on their mode of nutrition.

Tissue level of organization refers to the grouping of cells to form tissues that combine to form an animal body. There are no organs present in this level of organization. Example: Platyhelmenthes.

In cellular level of organization, a group of cells combine to form the whole body. Each cell carries over a specific function. This level of organization is also called as cell aggregate of body plan. Sponges exhibit this level of organization. Hydra exhibits tissue level of organization.

Cells performing same functions group together to form a tissue. Organs are absent in this level of organization. Cells are specialized with division of labour. Example for this level of organization is Hydra. Planaria exhibits organ level of organization.

Organs group to form organ systems. Each and every organ system is specialized to perform a specific physiological activity. Annelids exhibit this level of organization. Some of these animals are coelomates, few others are pseudo coelomates and others are acoelomates.

In open circulatory system, blood is pumped by heart into blood cavity. In closed circulatory system, blood is enclosed in blood vessels. Interstitial fluid is separated from blood in the case of closed circulatory system. Closed circulatory system is exhibited by chordates and open circulatory system is exhibited by mollusca and arthropods.

Sponges are asymmetrical. They contain uneven branches growing on their surface that makes them asymmetrical. Symmetry is also considered as the basis of classification. An animal is considered to be radially symmetrical if their body looks similar when cut in any radial direction. Examples: Colentrates and echinodermata. An animal is considered to be bilaterally symmetrical if their body looks when cut along the lateral direction. Examples: Annelids, Arthropods and humans.

The word “blasted” derives its origin from the word blastula which means a hollow ball of cells formed during the early stage of embryo. If the number of cell layers in blastula is two in number, i.e. ectoderm and endoderm, then such organisms are considered to diploblastic. If the number of cell layers in blastula is three in number, i.e. ectoderm, mesoderm and endoderm, then such organisms are considered to triploblastic. In diploblastic organisms, mesoglea, an undifferentiated substance, is present between endoderm and ectoderm.

Mesoderm gives rise to skeletal and muscle tissues, blood, lymph and connective tissues. Ectoderm gives rise to epidermis, hair, mammary glands and CNS. Endoderm gives rise to organs like stomach, pancreas, urinary bladder and intestines.

A digestive system with one opening to outside is called an incomplete digestive system and a digestive system with separate openings for ingestion and egestion is called complete digestive system. Platyhelmenthes and sea sponges have an incomplete digestive system.