Biodiversity. Principles of classification.

Before any study can be made of living organisms it is necessary to devise a scheme whereby their enormous diversity can be organized into manageable groups. This grouping of organisms is known as classification and the study of biological classification is called taxonomy. A good universal system of classification aids communication between scientists and allows information about a particular organism to be found more readily. There is no 'correct' scheme of classification since organisms form a continuum and any division of them into groups was proposed solely for human convenience.

During the eighteenth century, the Swedish botanist Linnaeus devised a scheme of classification which has become widely accepted. In this scheme organisms are grouped together according to their basic similarities. Relationships are based on homologous rather than analogous characteristics. Homologous characters are those that have a fundamental similarity of origin, structure and position, regardless of their function in the adult. Analogous characters are those that have a similar function in the adult but which are not homologous, i.e. they do not have the same origin. For example, wings of butterflies and birds are both used for flight but their origins are not similar. Classification based on homology is called natural classification. It now embraces biochemical and chromosome studies as well as the morphology and anatomy used by Linnaeus. A modern natural classification reflects the true evolutionary relationships of organisms.

The first colonies have arisen when individual unicells failed to separate after cell division. Within colonies each cell is capable of carrying out all the essential life processes. Indeed, if separated from the colony, any cell is capable of surviving independently. In this way, the individual cells within a colony have become different from one another in both structure and function, a process known as differentiation. Further changes of this type have finally resulted in cells performing a single function. This is known as specialization. With increasing specialization, and the consequent loss of more and more functions, cells have become increasingly dependent on others in the colony for its survival. This interdependence of cells must be highly organized. Groups of cells must be coordinated so that the colony carries out its activities efficiently. Such coordination between the different cells is called integration. Once the cells become so dependent on each other that they are no longer capable of surviving independently, then the structure is no longer a colony but a multicellular organism.

Did you know?

If one page was devoted to describing

each species of life on earth,

the total would fill 3.75 miles of bookshelf.

Grammar 1. Времена группы Perfect Active.

2. Придаточные предложения (дополнительные, определительные, обстоятельственные).

1. Найдите сказуемое в следующих предложениях. Определите его грамматическое время:

a) During the eighteenth century, the Swedish botanist Linnaeus devised a scheme of classification which has become widely accepted.

b) For example, wings of butterflies and birds are both used for flight but their origins are not similar.

c) The first colonies have arisen when individual unicells failed to separate after cell division.

d) The individual cells within a colony have become different from one another in both structure and function.

e) The interdependence of cells must be highly organized.

f) With increasing specialization cells have become increasingly dependent on others in the colony for its survival.

g) Once the cells become so dependent on each other that they are no longer capable of surviving independently.