Download 1 Ch 2.2b The Nitrogen Cycle A) The Nitrogen Cycle • Nitrogen is an

Science 10
Ch 2.2b notes
Name:__________________
Blk: ____ Date: _________
Ch 2.2b The Nitrogen Cycle
A) The Nitrogen Cycle
• Nitrogen is an important component of ______________ and _______________, which are
essential for life functions. Nitrogen is cycled through ecosystems through
__________________, __________________________, and ________________________.
B)
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Nitrogen Stores
The largest store: the __________________ as nitrogen (N2) gas.
Other major stores: ________________ and organic matter in _________________.
Smaller amounts: ____________________________________________________________.
I) Nitrogen fixation
• The conversion of nitrogen (N2) gas into compounds containing ________________(NO3 -) or
________________________ (NH4+).
• Nitrogen fixation occurs in 3 ways:
(a) In the atmosphere:
• __________________________(an atmospheric discharge of electricity) provides the
energy for N2 gas to react with O2 gas to form nitrate and ammonium ions.
• Compounds formed by these ions then enter the soil by _________________ (rainfall).
• This provides only a small amount of nitrogen fixation.
(b) In the soil:
• _________________________ convert N2 gas into ammonium ions by decomposition.
• E.g. The bacterium Rhizobium lives in the root of _____________________, which are
plants such as _____________________________________.
• The plants provide ___________________, while bacteria provide ________________.
(C) In the water
• Some species of ________________ convert N2 into ammonium during photosynthesis.
• They provide nitrogen compounds to plants in ________________________________.
II) Nitrification
• Important for plants that do not live in association with _________________________
(symbiosis); they must obtain nitrogen in the form of nitrate (NO3-) through nitrification.
• Nitrification is a two-step process:
(I) A certain species of nitrifying bacteria convert _______________ into ______________.
(II) A different species of nitrifying bacteria converts the ___________ into ____________.
III) Uptake
• Plants:
o Nitrates (NO3-) enter ___________________ through the process of uptake.
o These nitrogen compounds are incorporated into (made up) plant _______________.
• Animals:
• ____________ and ________________ eat the plants; they use nitrogen for DNA and
proteins.
• Decomposer _____________ and ________________ convert the nitrogen trapped in the
cells of dead organisms and convert it into ammonium (NH4+), recycling the nitrogen into
the soil.
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Nitrification:
Figure 2.35 (p. 80)
uptake by animals
Process D
1. Process A:
_____________________
2. Process B:
____________________
Step 1:_______________
Step 2:_______________
Process C
3. Process C:
_____________________
3. Process D:
______________________
______________________
C) How Nitrogen Is Returned to the Atmosphere and Removed from Ecosystems
• Denitrification: is the process through which nitrogen is returned to the _________________.
• In a balanced ecosystem:
o amount of ________________ nitrogen = amount of nitrogen _____________________
through denitrification
(I) Nitrogen can be returned to the atmosphere by:
• _____________________________ convert nitrate (NO3-)back into nitrogen gas (N2) through a
serious of chemical reactions.
• _______________________ returns nitrogen as ammonia (NH4+) in volcanic ash and
_______________________ gases such as nitrogen oxide and nitrogen dioxide.
(II) Nitrogen can be removed from ecosystems
• Excess nitrogen dissolves (mixes) with ____________________, enters the waterways, and
washes into lakes and oceans.
• Unused nitrogen may settle to ocean, lake or river bottoms in __________________ and form
sedimentary rocks.
• The nitrogen trapped in sedimentary rocks is not released until the rocks weathered.
D) Human Activities and the Nitrogen Cycle
• Human activities have doubled the amount of available nitrogen in the biosphere. This increase
has been due to the following:
• ____________________ combustion (burning) in power plants and motorized transportations
as well as __________________ release nitrogen oxide (NO) and nitrogen dioxide (NO2).
• Burning also releases nitrogen compounds that increase acid precipitation.
• Acid precipitation has a lower pH (higher acidity) than non-polluted rain.
• Acid precipitation has negative effects on forests, soils, and freshwater and the organisms.
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Agricultural practices often use large amounts of nitrogen-containing __________________.
• Excess nitrogen not used by plants is washed away or leaches into the waterways.
(Leaching = removal by ____________ of substances that have dissolved in moist soil.)
• Excess nitrogen promotes huge growth called eutrophication “blooms” in aquatic algae.
(Eutrophication = increased amount of nutrients result in increased plant ________________
and ___________________)
• Algal blooms use up CO2 and O2 and block sunlight, killing many aquatic organisms.
• Algal blooms can also produce __________________________ that poison animals.
Q: Think about how this can affect the food web!!!
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Review Questions:
1. Why is nitrogen necessary for living organisms?
2. How is nitrogen stored?
3. How is nitrogen cycled through the ecosystem?
4. What is nitrogen fixation?
5. What is nitrification and uptake?
6. How is the process of denitrification different from nitrogen fixation and nitrification?
7. How does nitrogen return to the atmosphere?
8. How is excess nitrogen removed from ecosystems?
9. How do human activities affect the ecosystem? List three human activities that increase the
amount of available nitrogen in the biosphere.
10. Excess nitrogen in the ecosystem increases the amount of algal blooms. List two negative
effects of algal blooms.
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