The term morphology as used by biologists refers to a study of the shape, structure, and size of plants, animals, and microorganisms, and of their parts. It is sometimes used synonymously with anatomy, although anatomy usually implies detailed study of either gross or microscopic structure. Interest in morphology, especially comparative morphology, was greatly stimulated when the concept of evolution was widely accepted. Prior to that time, similarities of form in different kinds of organisms was merely accepted as fact. Charles Darwin, on the other hand, regarded them as evidence that living organisms evolve by a series of steps from pre-existing forms. This view encouraged morphologists to look for similarities and differences in various forms of life in an effort to establish evolutionary relationships.
Early morphologists attempted to establish structural patterns within an organism, or between different types of organisms. Examples include comparisons of the bone pattern in the human foot, with those of the hand, or of the human arm with the wing of a bird. Stages of embryonic development were also compared. The aim of much of this work was to establish evolutionary relationships that could provide a natural classification system based on genetic similarities.
Developmental morphologists, who focus their attention on patterns of development as an organism grows from an ovum to seed to an adult, provide another approach to the study of form and structural relationships of living organisms. This approach is called developmental morphology, or morphogenesis. It attempts to furnish an understanding of the mechanisms responsible for development, and the ways in which adjacent parts of a developing organism influence the growth of neighboring structures.
The methods used by morphologist vary depending on the type of organism and the structural level of the study. Studies of gross structure rely on careful dissection and precise description of all parts. Tissues and cells are better studied microscopically, relying on histochemistry and autoradiography. Histochemistry makes use of dyes that differentially stain structural or molecular components in carefully prepared tissue samples. This technique allows the histochemist to identify acid or basic components, as well as the location of specific chemicals such as protein, DNA, or glycogen within the cell or tissue. It has also been possible to pinpoint the location of some enzymes using this technique.
Autoradiography involves supplying the tissue with a radioactive substance and allowing time for the components to interact. The tissue is then prepared and placed in contact with a photographic film or emulsion. Radioactivity causes the silver grains in the film to darken, and allows the scientist to locate sites where the substance has been concentrated.
Modern techniques such as transmission and scanning electron microscopy have provided the contemporary morphologist with a basis for comparative studies of the fine structure of cells and tissues in different organisms. They have also enabled study of the smallest components of cells, and have contributed to an understanding of the basis for the contraction of muscle cells and the movement of cilia and flagella in microorganisms.
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