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(Write these down)
Nitrogen Cycle summary questions
1.Nitrogen is available to plants generally in
which two chemical forms?
2.Which two things perform the process of
nitrogen fixation?
3.Describe the process of nitrogen fixation.
4.Denitrification is a chemical process that does
what?
5.What kinds of organisms perform
denitrification?
6.What kind of ecosystem accounts for more
than half of terrestrial denitrification?
The playa’s
Lightning
Nitrogen-fixing bacteria
Legumes
Decomposers
Denitrifying bacteria
Why Nitrogen is important
It’s a major component of Proteins!
It’s a major component of DNA !
The movement of nitrogen between
different groups of organisms and
between the different molecular
types is known as the nitrogen cycle
Here’s a problem…
Organisms can die of a Nitrogen deficiency
while being completely surrounded by it.
Remember, N2 is _______% of the
atmosphere
Unfortunately
Putting N2 into a
plant or animal is
like trying to fit a
square peg into a
round hole
Bottom line…N2
has to be changed
Lightning!!
The high energy in lightning can take
atmospheric Nitrogen, N2, and convert
it in mid air to Nitrates
If not lightning…
The only other natural way to get N2 into a
usable form, is to have a certain bacteria
Bacteria
These bacteria are called Rhizobium
Rhizobium
So Mr. Irvine, my
tomatoes died this
year because of a
Nitrogen deficiency.
Could
Rhizobium help
my garden?
Well Fiddy, here’s what you do…
Clover
Peas
Beans
Alfalfa
These plants have a symbiotic relationship
with the Rhizobium and will give your soil
these special bacteria.
Nice… Plants like NH4+
and NO3-
How do plants use the Nitrate
and Ammonium?
“Assimilation”
•Plants will build their biological
molecules such as Proteins and DNA…
Pretty important stuff!
Now to the Animals…
So how do consumers get their
Nitrogen for Proteins and DNA?
“Assimilation”
Death becomes it
Or Death becomes a PART of the
plant or animal
“For you are dust, And to dust
you shall return.”
Ammonification
Decomposers break apart the organic
molecules and return some of it back into
the soils, or water as inorganic ammonia
(NH3)
It can now be used again by the
producers…
What if plants don’t get to these
Nitrates?
Then they’re
OURS!
Denitrifying Bacteria
These guys convert Nitrates and nitrites
into Nitrogen Gas
Yeah, were
pretty gassy!
Conditions for Denitrification:
Anaerobic conditions… aka no oxygen
 Waterlogged fields
 High clay soils
 Swampy ecosystems
Over half!
Over half of the worlds Denitrifying bacteria are
found in anaerobic (no oxygen) ecosystems like
swamps and bogs
Yuk… so many
denitrifying
bacteria in here
Summary:
• Either Nitrogen-fixing bacteria or ____________
remove nitrogen gas (N2 ) from the atmosphere and
convert it to _________.
• ___________ take in nitrates and use them to
build biological molecules.
• _____________ disassemble nitrogen-containing
molecules in plants and animals and release
ammonium back into the soils.
• ____________ bacteria convert nitrates into
nitrogen gas which is released back into the
_______________.
Free response:
1. Nitrogen is critical for sustaining life in both terrestrial and
aquatic ecosystems.
a) Draw a fully labeled diagram of the nitrogen cycle (4 points)
b) Describe the following steps in the nitrogen cycle
i. Nitrogen fixation (1 point)
ii. Ammonification (1 point)
iii. Denitrification (1 point)
c) Describe one reason why nitrogen is crucial for sustaining life
on Earth (1 point)
d) Describe one way that the nitrogen cycle can be disrupted by
human activities. (1 point)
Now…
•Humans are altering some of the cycle. Your job
is to look at page 85, under “How are human
activities affecting the Nitrogen Cycle?” Look at
the fourth cause and write a few notes on the
subject.