4 Levels of Organization in the Animal Kingdom

Animals are characterized as being eukaryotic and multicellular. The animal kingdom classification is all about organizing entities into groups to study and understand them better. This orderly arrangement aids in comprehending the shared, common characteristic between individuals thereby defining the group. As per research, out of more than 10 million species of animals on earth, only 1.2 million species have been identified and grouped. This massive population of animals necessitates the need to classify. To a newly described or identified species, classification helps in allotting a systematic position. 

Kingdom Animalia is one among the 5 kingdoms of classification consisting of animals. It is the largest of all the kingdoms where entities do not possess a cell wall or chlorophyll and hence are termed as heterotrophs. Furthermore, Kingdom Animalia is classified into the following subphyla basis their body design, namely:

  • Porifera
  • Coelenterata
  • Platyhelminthes
  • Nematoda
  • Annelida
  • Arthropoda
  • Echinodermata
  • Protochordata
  • Vertebrata

All entities in the animal kingdom, despite being multicellular do not exhibit a similar model of the organization of cells. The following pattern or levels of the organization is observed in animals:

Cellular Level Of Organization

Animals exhibit a loose arrangement of cells as seen in sponges

Tissue Level Of Organization

Group of cells displaying similar functions are arranged into tissues, which is brought about by a division of activities in animal cells among themselves as seen in Coelentrates.

Organ Level Of Organization

A cluster of animal tissues performing similar functions are arranged to form the organs of animals which specifically performs a special function only as seen in Platyhelminthes  

Organ System Level Of Organization

A few organs, usually carrying out a major functionality form the organ system. These organs are associated to form the functional system, where each is concerned with a particular physiological function, it can be the digestive system, the respiratory system observed in chordates, echinoderms, etc.

The most important and fundamental units of this classification are the functional unit, the cell. Both in plants and animals, it forms the basis, and are often referred to as the building blocks of life. However, plant cell and animal cell vary greatly in their composition. Following are few of the important differences:

Plant cell
Animal cell
The cell wall is present
The cell wall is absent
Have a regular cell shape
Round and irregular cell shape
The nucleus is observed on one side of the cell
The nucleus is found in the center of the cell

Difference between Plant Cells and Animal Cells

As stated before, plant cells and animal cells share a few common cell organelles as both are eukaryotes. The function of all these organelles is said to be extremely similar lying between two classes of cells. However, major differences do exist between them which significantly reflect the difference in the functions of each cell. The major differences between the structure of animal and plant cells are as follows:

Plant Cell
Animal Cell
Cell shape
Has distinct edges, usually square or rectangular in shape.
Is irregular and round in shape.
Cell wall
Plasma membrane
Endoplasmic reticulum
Present and lies on one side of the cell
Present and lies in the centre of the cell
Present but are very rare
Golgi apparatus
Few large or a single, centrally positioned vacuole
Usually small and numerous
Most of the animal cells consist of cilia
Present, but fewer in number
Are present and are numerous
Essential nutrients
The plant cell can synthesize amino acids, vitamins and coenzymes
The animal cell cannot synthesize amino acids, vitamins, and coenzymes

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