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7.3.1. Autotrophic anabolism

Autotrophic anabolism

The anabolism is the synthesis of complex organic molecules from other simpler molecules with the energy provided by the phosphate bonds of the ATP and reducing power. ATP necessary may come from the catabolism of the photosynthesis or chemosynthesis

Before entering anabolism, we will remember the different forms of nutrition that living beings have.

Classification of organisms according to their form of nutrition

Living beings need to live:

  • source of carbon, necessary to build your organic biomolecules. Depending on your carbon source, we distinguish:
    • Autotrophic organisms: they take C from CO2 from the air.
    • Heterotrophic organisms: they use the C of simple organic molecules .
  • source of electrons (hydrogen) to reduce molecules. Depending on where it comes from in hydrogen, we distinguish:
    • Lithotrophic organisms: hydrogen comes from inorganic substances, such as H2O, H2S.
    • Organotrophic organisms: hydrogen comes from organic molecules.
  • source of energy that allows endergonic reactions to take place.
    • Phototrophic organisms, if they take advantage of the energy of light.
    • Chemotrophic organisms, if they use chemical energy.
  • An ultimate acceptor of electrons (hydrogens) that allows the former molecule to oxidize, releasing energy. They are distinguished:
    • Aerobic organisms, if oxygen is the last electron acceptor.
    • Anaerobic organisms, if it is another substance that accepts the electrons.
  • Water, mineral salts and nitrogen to build proteins and other nitrogenous compounds. 

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Canary Islands, July 2021, question 11

11. The classification of organisms can be carried out based on the processes they carry out to obtain matter and energy.

a. What are the organisms that obtain their energy from the oxidation-reduction of compounds in their environment called?
b. What are the organisms that obtain ATP by transformation of light energy called?
c. What source of Carbon do chemioautotrophic organisms use?
d. What source of Carbon do mushrooms use?


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