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Cell specialization


According to the degree of present complexity in the alive beings, the animals can classify themselves in different groups. In an ample group in the most primitive animals consider themselves included, which are unicellular and make all their vital functions with a single cell, existing within this cell a certain division of work; and we were with multicellular organisms in which the vital functions are going to be made by specialized cells. To greater specialization of the cells greater degree of complexity of the organism and also supposes that the cell is going to have a form and a structure that make it more apt to make the suitable function. In agreement with the different levels from association and cellular specialization a series of levels is recognized that are useful to make a classification of the animals.

First level

Protoplasmatic , protozoa , unicellular organisms

Second level

Cellular, the sponges would enter here; the organisms of this level are formed by associations of independent cells. They can appear in some cells a certain division of work. The specialized cells have little tendency to form layers, is to say do not form weaves.

Third level

Tissue, jellyfish. They have grouped cells forming a weave species. The nervous network is formed by a set of interconnected cells and specialized to transmit the impulses, it is spoken of primitive weaves.

Fourth level

Organic, the flatworms, these have many weave classes and some of these weaves are grouped in organs (gonads)

Fifth level

Level of system of organs, superior animals that besides to have weaves, have them grouped in organs and these in systems. These systems can present greater or smaller complexity and some of them serve us to classify.


Morphologic standards exist that condition the external appearance of the animal. The number of them is limited. These patterns consider the symmetry of the animal, the form of the head as well as the form of segmentation throughout the body, of equal way consider as the cavities of the body form.


It exists in most of animals one or several planes of symmetry that divide to the animal in equal parts, others by their irregular form do not present it (amoeba). Some protozoa as well as young the superior animal eggs and embryos are going to present specific symmetry, is to say gives rise that the planes that happen through the center divide to the animal in equal parts. Other more complex animals like hidras, sponges, jellyfish present broadcast symmetry. Form of cylinder squashed with a certain number of antimer denominated equivalent parts that leave a central axis. Superior in that it is observed the mouth denominates inferior buccal surface and or the aboral one. The superior animals present bilateral symmetry.

Another characteristic is the cavities of the body, are animals that do not have cavities and they are not denominated either coelome present mesoderm, others present/display false cavities, false coelome, is to say the cavities do not form from a mesoderm the pseudocoelome animals. Finally the coelome ones are those that have true coelome produced from the mesoderm.

The metamere

There are animals that present the body segmented in metamere (earthworm); others like the insects, arthropoda have the segmented body existing clear differentiation of the segmented ones. In the vertebrates the metamere is evident in the embryonic stages and tends to disappear in the adults.