Transcript The Nitrogen Cycle

The Nitrogen Cycle
Chapter 2
Nitrogen
• The circular flow of nitrogen to free gas in the atmosphere
(it is 78% of our atmosphere), to nitrogen compounds (such
as nitrates) in the soil, back to atmospheric nitrogen.
• In it’s elemental form (not a compound), it is a colorless,
odorless gas.
• It must be combined with oxygen or other elements before
it becomes available as a nutrient for living organisms.
• Plants and animals use nitrogen compounds to form DNA
and proteins and vitamins.
Nitrogen Cycle
• Nitrogen fixation-a process by which nitrogen gas
from the atmosphere is converted to nitrates.
• This can happen in several different ways:
– Nitrogen-fixing bacteria can convert gas to nitrates.
• Some of these bacteria live in the soil, and others live in
nodules on the roots of legumes (like beans).
– Several industrial processes convert the gas to
nitrates.
• Ammonia gas (a by-product of steel making) can be
converted to nitrates. These nitrates are used as fertilizers.
Nitrogen Cycle continued…
– Nitrogen fixation also occurs naturally when
lightning strikes .
– Nitrates are also released when plants and
animals decay, or from animal wastes.
Nitrogen Cycle continued…
• Denitrification is the process where nitrates
are broken down and the nitrogen is released
back into the atmosphere.
– Happens by some bacteria
– Also happens when nitrates are carried off by
surface water, which constantly exchanges
nitrogen with the atmosphere.
The Nitrogen Cycle, with pictures and
arrows…
• Please look at Figure 2-10, on page 27.