We know that living organisms are characterized by certain structural and functional features which set them apart from the nonliving world. One of these features is the phenomenon of metabolism. In the broadest sense, metabolism refers to the sum total of all the chemical charges or reactions which take place in a living organism.
However, the term is often used in a more restricted sense to include only those chemical reactions which occur within individual cells. According to this definition, then, metabolism is entirely a cellular phenomenon, and the term can be applied to a multicellular organism only in the sense that it exhibits multiple cellular organisms only in the sense that it exhibits multiple cellular characteristics.
This viewpoint would not take into consideration any aspects of organismic metabolism which might consist of emergent properties.
The metabolic link between photosynthesis and finished living matter is a large variety of synthesis reactions. These produce the chemicals that a cell does not obtain directly as prefabricated environmental nutrients or as secretions from other cells.
Such missing ingredients include most of the critically necessary compounds for cellular survival: nucleic acids, structural and enzymatic proteins, polysaccharides, fats, and numerous other groups of complex organic substances. In most cases such synthesis reactions are endergonic and ATP-requiring.
A cyclical interrelation is therefore in evidence. On the one hand, breakdown of organic compounds leads to a net build up of ATP through respiration. On the other, breakdown of ATP leads to a net buildup of organic compounds through chemicals synthesis.
Essentially, metabolism consists of three phases: nutrition, synthesis, and respiration. Nutrition is that aspect of metabolism by means of which the raw materials for synthesis and respiration are supplied. Synthesis is that aspect of metabolism during which protoplasm or protoplasmic components...
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