Download 4.3 * The Nitrogen Cycle - Science 10 With Mr. Francis

4.3 – THE NITROGEN
CYCLE
Science 10
Mr. Francis
WHY DOES NITROGEN
MATTER
 Nitrogen is an important element in the formation of nucleic acids
and amino acids (building blocks of proteins).
 Nitrogen gas is the most abundant material in the atmosphere
(N2 78%)
 Nitrogen gas contains a strong triple bond that most organisms
can’t break, so nitrogen gas cannot be used by most organisms
 Nitrogen gas must be changed into a useable for of nitrogen
through the processes of nitrogen fixation, nitrification, and
denitrification.
NITROGEN CYCLE
NITROGEN FIXATION
 Nitrogen fixation is the process through which nitrogen gas (N2) is
“fixed” or combined with hydrogen (H2) to produce Ammonia (NH3).
 Roots of legumes (beans, alfalfa, etc) have a symbiotic relationship
with nitrogen fixing bacteria. The bacteria generate ammonia, some is
used by the plant, the remainder enters the soil.
 Ammonia (NH3) mixes with water to form Ammonium (NH4+)
 Lightning can also “fix” nitrogen into Ammonia.
NITRIFICATION
 Nitrifying bacteria perform the process of nitrification, converting
ammonium (NH4+) into Nitrite (NO2-) and then Nitrate (NO3-).
 Nitrate can be taken up by plants through there roors.
 This nitrate is part of the building blocks of plant proteins.
 Animals obtain nitrate to make animal proteins from eating plants
or animals that eat plants.
DENITRIFICATION
 When organisms die decomposers break their proteins and nucleic
acids down into ammonia and nitrates.
 The process of denitrification (you guessed it, carried out by
anaerobic denitrifying bacteria) converts ammonia and nitrates back
into Nitrogen gas which is returned to the atmosphere.
THE QUESTIONS
 Page 95 Questions #1-13,15,17