Transcript Document

UNIT
7
Ecosystems II: matter and energy
THE NITROGEN CYCLE
Biology and Geology 4. Secondary Education
UNIT
The nitrogen cycle
7
• Even though air contains 78%
nitrogen (N2) by volume, this gas
is unavailable for use by most
living things. Only certain kinds of
soil bacteria can harness it.
ATMOSPHERE
N2-fixing bacteria
NO3- Nitrates
Excretion
Absorption
Feeding
Decomposition
by bacteria
Denitrifying bacteria
Nitrogen (N2)
Nitrifying
bacteria
NO2- Nitrites
Biology and Geology 4. Secondary Education
NH3 Ammonia
• Producers can only use
nitrogen in the form of soluble
mineral salts (nitrates).
Consumers and decomposers
take in nitrogen with their food.
• Atmospheric nitrogen is
transformed into nitrates that
producers can use through
lighting and through fixation
carried out by different kinds of
soil bacteria.
• Nitrates can leave the cycle
when water transports them to a
sedimentary environment, where
they will precipitate and form
sedimentary rocks.