Energy in biochemistry

In principle, all rules for exothermic and endothermic reactions are the same in biochemistry, including the processes in living creatures. There also we can find chemical reactions that deliver or cost energy.
But in living creatures, energy often is transferred via specific substances like ATP (Adenosine Tri Phosphaat), a molecule that often appears in reactions with energy transport.
Most living items must breath, where the main purpose is collecting Oxygen.
Green plants have also another option: the photosynthesis that is about the opposite of respiration. In the photosynthesis, Oxygen is produced in stead of used.
Respiration and photosynthesis are not the only biochemical processes with a real energy effect; in fact all biochemical reactions are exothermic or endothermic, but we wan't deal with that now.

Photosynthesis and respiration
Two important processes in nature, one the opposit of the other:
  1. the respiration: C6H12O6 + 6O2 6CO2 + 6H2O     exothermic(ΔH < 0)

  2. the photosynthesis: 6 CO2 + 6H2O C6H12O6 + 6O2       endothermic (ΔH > 0)

Not only men and animals, but also plants "breath"!
Contrarily to the photosynthesis, respiration needs chemical energy from outside the organism. (for example in the form of sugar).
The photosynthesis however produces chemical energy. (for example ATP and the sugars that can be consumed in respiration).
Plants have both possibilities; by day the photosynthesis dominates (under influence of light) and by night dominates the respiration.