ABSTRACT
Gas exchange is among the most important interactions
between organisms and their environment. Oxygen (O2)
and carbon dioxide (CO2) production and consumption are
fundamental to photosynthesis and aerobic respiration,
while anaerobic respirations produce CO2 and methane
(CH4). Sulfate reduction produces hydrogen sulfide (H2S)
and other reduced gaseous sulfur compounds, while deni-
trification generates di-nitrogen (N2) as well as nitrous
oxide (N2O) and nitric oxide (NO). These and other nitro-
gen gases, including other oxides of nitrogen (NOx) and
ammonia (NH3), leave and enter the gas phase through
such biological reactions as nitrogen fixation and deamina-
tion. Water vapor is another gas of critical importance in
biological systems, with losses through evaporation, tran-
spiration, perspiration, and/or respiration causing dehydra-
tion, loss of turgidity, and in extreme cases death.
