Biogeochemical
Cycles
• BIO.5.2
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ISN p. 41
Biogeochemical cycles
• Unlike the one way flow of energy, matter
is recycled within and between
ecosystems.
• Elements, chemical compounds, and other
forms of matter are passed from one
organism to another and from one part of
the biosphere to another through
biogeochemical cycles.
• Matter can cycle through the biosphere
because biological systems do not use up
matter, they transform it.
ISN p. 41
Biogeochemical cycles
• Every living organism needs nutrients to grow and carry out
essential life functions. Like water, nutrients are passed
between organisms and the environment through
biogeochemical cycles.
• Because nutrients are often in short supply, recycling
nutrients is essential for life in an ecosystem.
• Nutrient cycling also prevents many chemicals from reaching
concentrations which would be toxic, or harmful to
organisms.
ISN p. 41
Biogeochemical cycles
• Ecologists are often interested in the primary
productivity of an ecosystem.
• Primary productivity is the rate at which organic
matter is created by producers.
• When an ecosystem is limited by a single nutrient
that is scarce or cycles very slowly, this substance is
called a limiting nutrient.
The Hydrological/Water cycle-
The Carbon/Oxygen cycle
CO2 in
atmosphere
CO2 in
atmosphere
CO2 in
ocean
The Nitrogen cycle
N2 in Atmosphere
NH3
NO3- &
NO2-
The Nitrogen cycleAtmospheric nitrogen (N2) makes up nearly
78%-80% of air.
Organisms can not use it in that form.
Lightning and bacteria convert nitrogen into
usable forms.
• All organisms require nitrogen to make amino acids which in turn are
used to build proteins.
• Free nitrogen (N2) makes up about 78% of Earth’s atmosphere, but it
cannot be used in this form.
• Although nitrogen gas is the most abundant form of nitrogen on Earth,
only certain kinds of bacteria can use this form directly. These bacteria
live in the soil and on the roots of plants called legumes.
• Legumes are plants that produce protein substitutes, such as soybeans
and peanuts. These plants have lumps on their roots called nodules in
which bacteria live.
The Nitrogen Cycle
• Nitrogen is converted by these bacteria to ammonium nitrate
(NO3-) in a process called nitrogen fixation. This is extremely
important for plants and animals to build proteins.
When organisms die, decomposers return nitrogen to the soil
as ammonia. Other soil bacteria convert nitrates into
nitrogen gas in a process called denitrification.
The Phosphorous cycle-
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The Phosphorous cycle• Over time, rain and weathering cause rocks to release
phosphate ions and other minerals. This inorganic phosphate is
then distributed in soils and water.
• Plants take up inorganic phosphate from the soil. The plants may
then be consumed by animals. Once in the plant or animal, the
phosphate is incorporated into organic molecules such as DNA.
When the plant or animal dies, it decays, and the organic
phosphate is returned to the soil.
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• Within the soil, organic forms of phosphate can be made
available to plants by bacteria that break down organic
matter to inorganic forms of phosphorus. This process is
known as mineralisation.
• Phosphorus in soil can end up in waterways and
eventually oceans. Once there, it can be incorporated into
sediments over time.
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Extra Video
• https://youtu.be/Bn41lXKyVWQ
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