3.  Nitrogencomprises 78.08 % of the
atmosphere making it the largest
constituent of the gaseous envelope that
surrounds the Earth.
 Nitrogenis important in the make up of
organic molecules like proteins and DNA.
 Mostorganisms cannot use nitrogen in this
form, i.e N2

4.  Plantssecure their nitrogen in “fixed” forms
i.e incooperated in compounds such as:
Nitrate ions NO3
Ammonia NH3
Urea (NH2)2CO
 Animalssecure their nitrogen (and all other
compounds from plants (or animals that
have eaten plants).

5.  Four processes participate in the cycling
of nitrogen in the biospere:
• Nitrogen fixation
• Decay
• Nitrification
• Denitrification
*microorganisms play major roles in all
processes*

6.  Thenitrogen molecule is quite inert. To
break it apart so that its atoms can
combine with other atoms requires the
input of substantial amounts of energy.
 inert-nonreactive gas during chemical
synthesis, analysis or preservation of
reactive materials

7.  Three processes are responsible for most
of the nitrogen fixation:
1. Atmospheric fixation
2. Biological fixation
3. Industrial fixation

8.  Theenormous energy of lightening
breaks nitrogen molecules and enables
then to combine with oxygen in the air
forming nitrogen oxides.
 These dissolve in rain forming nitrates
that are carried to the earth.
 *contributes 5-8% of total fixed*

9.  Made synthetically via Haber Process.
 Nitrogenand hydrogen reacted under
great pressure and temperature in the
presence of a catalyst to make ammonia.
 Ammonia applied directly to farm fields
as fertilizers or further processed with
oxygen to make nitric acid.

10.  Theability to fix nitrogen is found only in
certain bacteria and archaea.
 Some live in symbiotic relationship with
plants of the legume family Rhizobium
 Some establish symbiotic relationships
with animals
 Some live free in soil

11.  Biological
nitrogen fixation requires a
complex set of enzymes and a huge
expenditure of ATP

12.  Protein
made by plants enter and pass
through food webs at each level.
 Ateach trophic level metabolism
produces nitrogen compounds that
return to the environment in excretions.
 Microorganisms break down the
molecules in excretion and dead
organisms into ammonia, NH3.

13.  Most of the ammonia produced by decay
is converted into nitrates.
Bacteria of the genus Nitrosomonas
oxidize NH3  nitrites NO2
Bacteria of the genus Nitrobacter
oxidize nitrites  nitrates NO3

14.  Thisis the reduction of nitrates to
nitrogen gas, thus replenishing the
atmosphere
 Anaerobic bacteria use nitrates as an
alternative to oxygen in their respiratory
process.
 Closing the nitrogen cycle

15. A side product of this reaction is known
as nitrous oxide N2O, more commonly
known as “laughing gas”
A mild anesthetic, also a greenhouse gas
that contributes to global warming,

19.  Carbon, C is one of the most common
elements on Earth.
 Its found:
4. in the tissues of living organisms
5. in the atmosphere
6. dissolved in ocean water and
7. locked up in limestone deposits that line
the ocean floor

20.  Living organisms provide two important
steps in the carbon cycle.
r Plants absorb CO2 from the atmosphere
to use during photosynthesis
2 Other organisms release CO2 into the air
during respiration

21.  In addition there are several important
non-organic storage areas of carbon in
the environment:
a A large portion is stored in rocks
i Oceans hold a large amount of CO2
because it dissolves easily in water
l Coal, oil and limestone store carbon that
once form ancient organisms
**burning fossil fuels will release CO2 into
the atmosphere**

22.  Photoautotrophsconstantly remove
carbon dioxide through the process
photosynthesis.
 Certainbacteria known as
chemoautotrophs use carbon dioxide to
synthesize the organic compounds they
need.

23.  Thecarbon present in food made by
plants reaches animals through the food
chain.
 Carnivorousanimals receive this carbon
when they eats animals.

24.  Carbon dioxide is continuously dissolved
in water bodies by diffusion.
 Once dissolved it either remains in the
waters or gets converted into carbonates
-2
CO3 and bicarbonates HCO3

25.  Thedissolved carbon dioxide is used by
plants for photosynthesis.
 Thecarbonates are converted into
calcium carbonate by certain marine
organisms.
 Thecalcium carbonate is used by corals
and oysters to make their shells.
 When these organisms die their shell
deposit to the sea floor and eventually
turn into sedimentary rocks.

26.  When plants and animals die and get
buried under the ground, after millions of
years they change into fossil fuels due to
high pressure and other physical and
chemical changes.

27.  Carbon dioxide is regularly returned to
the atmosphere by the process of
respiration in plants and animals.
 Burningof wood and fossil fuels in
industry and automobiles also releases
carbon dioxide.

29.  Itabsorbs infrared light. The atmosphere
absorbs more heat than i