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Updated: June 8, 2025
As to origin, they supposed that cells arose by a sort of crystallization from a mother liquor; and as to structure, they looked upon the cell-wall as the really important part, the fluid contents being quite subordinate.
Two long cilia protrude through the cell-wall, and effect the rapid locomotion of this "monad," which, in all respects except its mobility, is characteristically a plant. Under ordinary circumstances, the Chlamydomonas multiplies by simple fission, each splitting into two or into four parts, which separate and become independent organisms.
The relatively rigid nature of the plant cell-wall, and the attenuated inorganic food-supply of plants, make possible and necessary a form of growth in which the greatest surface is exposed to the exterior, and thus the plant body is composed of flattened laminae and elongated branching growths.
Food particles and waste. 5. Cell-wall. 6. Masses of active material found in certain cells, called plastids. Surrounding the nucleus is the main body of the cell, sometimes referred to as the "protoplasm." Since the protoplasm forms all parts of the cell, this substance is more properly called the cytoplasm, or cell plasm.
Schwann burdened his enunciation of the "cell theory" with two false suppositions; the one, that the structures he called "nucleus" and "cell-wall" are essential to a cell; the other, that cells are usually formed independently of other cells; but, in 1839, it was a vast and clear gain to arrive at the conception, that the vital functions of all the higher animals and plants are the resultant of the forces inherent in the innumerable minute cells of which they are composed, and that each of them is, itself, an equivalent of one of the lowest and simplest of independent living beings the Torula.
Hugo von Mohl applied to the fluid contents of the cell the term "protoplasm," and Max Schultze showed that this protoplasm is really identical in all organisms, plants and animals, also that the cell-wall is frequently absent in many animal tissues and in many unicellular forms, indicating that the protoplasm is the really important substance.
The most obvious distinction is that the animal cell-wall is either absent or composed of a nitrogenous material, whereas the plant cell-wall is composed of a carbohydrate material cellulose. The animal and the plant alike require food to repair waste, to build up new tissue and to provide material which, by chemical change, may liberate the energy which appears in the processes of life.
Through its activity chiefly is carried out that miracle of human physiology, the process of repair. By the transformation of its protoplasm the surplus food-materials of the times of plenty are stored away within its cell-wall against the time of stress.
Little by little the taut guy-ropes, lathes, braces, joists, all sagged and melted together, each cell-wall becoming dynamic, now expanding, now contracting; the ceilings vibrant with waving legs, the floors a seething mass of jaws and antennæ. By the time it was dark, the swarm was dropping in sections to the floor. On the following morning new surprises awaited me.
Surrounding and inclosing the cytoplasm, in many cells, is a thin outer layer, or membrane, which affords more or less protection to the contents of the cell. This is usually referred to as the cell-wall. A fourth part of the cell is also described, being called the attraction sphere. This is a small body lying near the nucleus and coöperating with that body in the formation of new cells.
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