Biogeochemical Cycles
• Defined:
Movement of
water through
the Earth and its
atmosphere
• 75% of the
Earth is covered
in water
• Less than 1% is
drinkable.
• Most water is
salty or frozen
Water Cycle Pathway
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• Evaporation: Heat changes water from a liquid to a gas
• Transpiration: Water evaporates from the leaves of plants
through openings called stomata
Water Cycle Pathway
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• Water vapor starts to cool…condensation occurs
• Condensation: process where water vapor turns into a
liquid
Water Cycle Pathway
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• Precipitation: Rain, snow, sleet, or hail falls when water drops
become heavy
• Runoff: Water runs down hill into rivers, lakes, streams, oceans…
• Infiltration: Water soaks into the soil and collects as groundwater
Oxygen Cycle
O2
O2
• Autotrophs: Release O2 into atmosphere by photosynthesis
• Most life needs O2 for cellular respiration
– Creates ATP (energy) for cells
CO2
CO2
CO2
CO2
CO2
Carbon
(C)
Cycle
CO
CO
2
CO2
CO2
2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
glucose
glucose
glucoseCO2
glucoseglucose
Carbon
• Plants
– Absorb CO2 for photosynthesis
– Release glucose (C6H12O6) after photosynthesis
glucose
CO2
CO2
CO2
CO2
CO2
Carbon
(C)
Cycle
CO
CO
2
CO2
CO2
2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
glucose
glucose
glucoseCO2
glucoseglucose
Carbon
• Animals
– Glucose passed up the food chain
– CO2 exhaled into atmosphere
glucose
CO2
CO2
CO2
CO2
CO2
Carbon
(C)
Cycle
CO
CO
2
CO2
CO2
2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
glucose
glucose
glucoseCO2
glucoseglucose
Carbon
• Decomposers
– Obtain glucose by feeding on dead organisms
– Carbon released in their waste
glucose
CO2
CO2
CO2
CO2
CO2
Carbon
(C)
Cycle
CO
CO
2
CO2
CO2
2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
CO2
glucose
Carbon
glucose
glucoseCO2
glucoseglucose
glucose
• Human Contribution
– Release excess CO2 into atmosphere when fossil fuels (coal, oil,
natural gas) are burned for energy
– Cycle is out of balance
Phosphorus (P) Cycle
P
P
P
P
P
• Phosphorus
needed to
make ATP,
DNA, lipids
• Problem: No
phosphorus in
atmosphere
• Step 1:
Phosphorus
released by
weathering of
rocks
• Step 2:
Producers
absorb P
through their
roots
Phosphorus (P) Cycle
P
P
P
P
P
• Step 3:
Consumers
ingest P
• Step 4:
Decomposers
obtain P
when feed on
the dead.
• Step 5:
Decomposers
release P
within waste
back into soil
or water
• Cycle repeats
Phosphorus (P) Cycle
P
P
P
P
P
P
• Human
Contribution
– Adding
excess P from
fertilizers
– P washes into
lakes, etc…
– Excess P
causes
extreme
plant & algae
growth
Nitrogen (N) Cycle
N2
N
N
N
N
Usable N
Nitrogen
fixation
N
Usable N
• Nitrogen needed
to build nucleic
acids (DNA/RNA)
• Problem:
Nitrogen in
atmosphere (N2)
is unusable
• Step 1: Bacteria
in soil convert N2
into usable
forms
• Step 2: Bacteria
absorb usable N
• Step 3: Bacteria
release N waste
into air
Nitrogen (N) Cycle
N2
N
N
N
N
Usable N
Nitrogen
fixation
N
Usable N
• Step 4:
Producers
absorb N
through their
roots
• Step 5:
Consumers
ingest N
through the
food chain
• Step 6:
Decomposers
obtain N from
dead
organisms…
return N to soil
in their waste
Nitrogen (N) Cycle
O2
ONO
O
N2
N
N
NO
O2
NON2
NO
NO
O2
N2
N
NO
O2
O
• How does lightning help?
– Energy breaks atmospheric nitrogen into Nitrogen oxide
– Nitrogen oxide falls in rain to soil
Review
1) Name and define the 6 stages of the water cycle.
2) How is oxygen released into the atmosphere?
3) In which cellular process is oxygen removed and used from the
atmosphere?
4) What are the 4 major types of organic molecules?
5) In which cellular process is carbon dioxide released into the
atmosphere?
6) How are humans disrupting the carbon cycle?
7) Which objects release phosphorus over time?
8) How are humans disrupting the phosphorus cycle?
9) Which organisms help convert gaseous nitrogen into a usable form
of nitrogen in the nitrogen cycle?
10) How do plants obtain nitrogen?
11) Of the major molecules that we have studied this year, which ones
contain nitrogen and/or phosphorous?