5th grade topic 1
 What are the different ways humans impact the nitrogen cycle – examples – fertilization
and burning of fuels
o Productivity – humans use nitrogen-containing fertilizers to enhance
productivity of plants, for example. Even if a plant has unlimited amounts of
other resources, it’s productivity is limited by nitrogen levels, and farmers are
attempting to control that
o Plant species diversity – plant species are adapted to function under a nitrogen
constraint, and an overabundance of nitrogen benefits plant species that are
evolved to take full advantage of higher nitrogen levels. These genetically gifted
plant variations out compete the other variations, and biodiversity decreases.
o Increased levels of nitrogen also cause acidification of aquatic systems and
adverse effects on fish
o Increased levels of nitrogen also causes eutrophication, causing a decrease in
levels of oxygen in aquatic ecosystems.
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5 grade topic 2 – how is nitrogen lost from the cycle
 Denitrification
o Bacteria changes nitrate in the soil to atmospheric nitrogen, which joins the
atmosphere.
 Volatilization
o Turns urea fertilizers and manures on the soil surface into gases that also join
the atmosphere
 Runoff
o The nitrogen in fertilizers and manure and the nitrogen in the soil is carried into
our rivers and streams — a concern for water quality.
 Leaching
o Nitrates are carried so deep into the soil that plants can no longer use them
o Produces a dual concern — for lost fertility and for water quality, as nitrates
enter the groundwater and the wells that provide our drinking water.
4th grade topic 3
 What is the role of animals in the nitrogen cycle
 Animals consume nitrogen when they consume plants or other animals. The nitrogen
circulate in their bodies and assists with bodily functions. When animals produce
nitrogen rich waste or die, bacteria decompose the waste and release it into the
atmosphere, where the free nitrogen reenters the cycle.
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4 grade topic 4
 What is the process when nitrogen in the air becomes a part of biological matter
through the actions of bacteria and algae
o Nitrogen fixation – free pure nitrogen is very inert an nonreactive and must be
combined with other elements into usable compounds
o Nitrogen fixing bacteria and algae convert pure nitrogen into ammonia, which is
absorbed by plants
o Bacteria of the genus rhizobium also live inside nodules inside plant roots and
secret nitrogen compounds in exchange from nourishment from the host plant
o Lighting can also fixate nitrogen – the high levels of energy combine nitrogen
with oxygen and form usable nitrates
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3 grade topic 5

What human activities affect the nitrogen cycle?
o Fertilizers and burning fossil fuels – increases in amounts of nitrogen in the
nitrogen cycle, which enhances productivity of certain plants and reduces
biodiversity of plant species,
o Increases in the amount of acid in the soil hurts plants
 also hurts aquatic animals by leading to anoxia or absence of oxygen in
the water
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3 grade topic 6
 what are legumes – plants that convert atmospheric nitrogen into plant usable nitrogen
o contain symbiotic bacteria called Rhizobia attached to their roots
o these bacteria are nitrogen fixing bacteria that convert pure, inert nitrogen into
nitrogen that is usable by other organisms – usually ammonium
o this is why legumes are right in protein and nitrates, as nitrogen is essential in
making amino acids and proteins
2nd grade topic 7
 why do plants need nitrogen – grow, develop, produce seeds
o used by the plant to produce enzymes and other proteins, as nitrogen is
essential to amino acids
o also used to make DNA, which has a nitrogen base
o essential to the growth of leaves and stems, and plants that are nitrogen
deficient will have yellow, sickly looking leaves
 cannot use pure nitrogen – have to use ammonia or other nitrates
2nd grade topic 8
 why do organisms require nitrogen
o same as plants – use to make amino acids and DNA
o animals do not use nitrogen gas or nitrates – they get usable compounds from
consuming other sources of nitrogen – animals break down protein into amino
acids for cell function
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1 grade topic 9
 How much of earth is composed of nitrogen
o 80% of the Earth – nitrogen is not stable in a crystal lattice, so it is not found in
the soil as much as its found in the atmosphere
o it is very inert and nonreactive as a gas, so it exists as a gas in the atmosphere in
much higher quantity than oxygen or any other element.
Million dollar answer
 1. Nitrogen fixation converts atmospheric nitrogen into ammonia, through bacteria or
lightning. – brings nitrogen into the soil where it can be nitrified
N2  NH3
 2. Nitrification is the converts the ammonia to nitrate through bacteria – makes the
nitrogen usable to plants and animals – most plants and animals cannot use ammonia
NH3  NO2  NO3
 3. Assimilation is when the inorganic nitrogen is taken up by the roots of the plants and
becomes apart of the food chain – used to make amino acids and DNA
NO3  organic nitrogen
 4. Ammonification is the conversion of organic nitrogen into ammonia - decomposition
of animals or animal waste converts the nitrogen into ammonia, which is available for
other biological processes
Organic nitrogen  NH3
 5. Dentrification is when nitrates are returned to the atmosphere by anaerobic bacteria
– the nitrates are converted into gaseous nitrogen and released into the atmosphere
NO3  N2