Energy and Respiration

autotrophs = organisms that can use inorganic carbon in the form of CO2, to procure their own energy.

heterotrophs = organisms that need a ready-made organic supply of carbon, because they cannot procure energy themselves.


Energy is needed by all living organisms in order to do work. By work we mean:

1. Anabolic Reactions (The synthesis of complex substances from simpler ones)

  • Synthesis of polysaccahrides from monosaccharides
  • Synthesis of lipids from glycerol and fatty acids
  • Synthesis of polypeptides from amino acids
  • Synthesis of nucleic acid from nucleotides

2. Active transport

3. Mechanical Work

  • Muscle contraction
  • Ameobid movement
  • Movement of cilia and flagella
  • Movement of vesicle in the cytoplasm

4. Bioluminescence or electrical discharge in some cases.

Endotherms are organisms that use the thermal energy released (basically recycle it) from metabolic reactions to maintain a constant body temp.

Ectoherms are organisms that use energy from outside their body to heat up.


Energy is made available in more ways. For example in aerobic conditions, a very high quantity of energy is released from the complete oxidation of glucose. Because this reaction has a very high activation energy, and the yield is huge, a much more flexible molecule is used: ATP (Adenosine Triphosphate)



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