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7.1. Metabolism


The metabolism is the set of biochemical and physicochemical processes occurring in the reaction cell and the organism, in which matter and energy are exchanged with their environment.

The main goals of metabolism are:

  • Obtain chemical energy, which is stored in the phosphate bonds of ATP.
  • Transform chemical substances from the outside of the cell into molecules that can be used by the cell.
  • Construction of own organic matter from energy and molecules obtained from the environment. This organic matter stores a large amount of energy in the bonds.
  • Destruction of these molecules to obtain the energy they contain.

The metabolism is divided into two phases interrelated occur simultaneously:

  • Energy obtaining phase: In catabolism, the transformation of complex organic substances into simpler molecules occurs, storing the chemical energy released in the form of phosphate bonds of ATP.
  • Organic matter construction phase: In anabolism, complex organic matter is built from simple molecules of the cytoplasm, using the energy obtained in catabolism or in other processes, such as photosynthesis and chemosynthesis.

Depending on the carbon source they use to build their biomolecules in anabolism, cells can be:

  • Autotrophs: their carbon source isatmospheric CO2, and depending on where they get their energy from, they can be:
    • Photoautotrophs: they get energy from sunlight.
    • Chemoautotrophs: they obtain the energy from the bonds of inorganic molecules.
  • Heterotrophs: they incorporate carbon through organic molecules. They obtain energy by breaking the bonds of organic molecules.

All metabolic reactions are regulated by specific enzymes.

In relation to catabolism, we will distinguish the following processes:

  • Respirationthe final electron acceptor is an inorganic molecule.
    • Aerobic respiration: the hydrogen acceptor is O2.
    • Anaerobic respiration: the hydrogen acceptor is not O2.
  • Fermentation: the final electron acceptor is anorganic molecule.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.