Overview
Biogeochemical cycles describe the movement
of a compound through the Earth’s four spheres
• Some cycles occur in a short amount of time (water),
while others take months or years (rock).
• Microbes (decomposers) play an important role in the
nitrogen and carbon cycles by returning nutrients to
the soil. This allows primary producers to grow.
• All the cycles involve the physical change of the
compound (e.g. water in its gaseous and liquid forms)
• Reservoir: Components of the cycle are stored for an
indeterminate period of time
Earth as a Closed System
Nothing can enter or exit the Earth except for heat.
Compounds must be recycled to sustain continuos life.
Water Cycle
Water cycles through the hydrosphere,
atmosphere, and lithosphere.
Steps
• 1. Evaporation: Solar energy creates water vapor,
which is responsible for clouds
• 2. Precipitation: Rain returns water back to the
hydrosphere and lithosphere
• 3. Surface Runoff: Water on the surface flows back
to the hydrosphere through a watershed.
• 4. Transpiration: Plants draw water through roots,
and evaporation from the leaves returns it to the
atmosphere.
Water Cycle: Importance
• 1. Purifies: Solutes (solids that dissolve in water)
are not evaporated
• 2. Distributes: Wind creates cloud movement, which
causes precipitation to occur in other places
• 3. Food Chain: water is needed for photosynthesis,
which allows plants to create sugars for fruit and
vegetable formation.
• 4. Life: Animals need a constant supply of water for
survival
Water Cycle
Carbon Cycle
Carbon is added to the atmosphere through burning
and respiration, and returned to the soil through
microbial fixation
Steps
*Notice the main purpose is to return
carbon from the atmosphere to the soil.
• 1. Photosynthesis: Plants consume CO2 from the atmosphere
to make sugars and O2.
• 2. Fixation: Microbes decompose carbon-based lifeforms and
enrich the soil with nutrients for plant growth.
• 3. Respiration: Animals consume plants for energy, breathe in
O2, and exhale CO2. This returns carbon to the atmosphere.
• 4. Burning: Humans burn carbon-based fuels for energy,
which returns carbon to the atmosphere (global warming?)
• 5. Sink: Fossilized carbon-based lifeforms can exit the carbon
cycle for millennia.
Carbon Cycle FRQ
Practice MCQ
The main abiotic source of carbon in the
environment for the carbon cycle comes from:
a. Carbon dioxide in the air
b. Carbon dioxide in the water
c. Carbon monoxide in the air
d. Carbon monoxide in the water
e. Carbonates in the air and water
Practice FRQ 1
Practice FRQ 2
• Water is important for all living organisms. The
functions of water are directly related to its physical
properties.
• a. water serves as a reactant and a product in the
carbon cycle. Discuss the role of water in the
carbon cycle.
• b. Discuss the impact of one human activity on
the water cycle.
MCQ 2
1. During the carbon cycle, which of the following carbon compounds
would be utilized as an energy source by heterotrophs? (90:36)
A. calcium carbonate
B. carbonic acid
C. organic molecules
D. carbon dioxide
E. carbon monoxide
Biogeochemical Cycles FRQ
a, c, b, d only
Key Terms
Ammonification: bacteria and fungi convert decomposing animal
and plant material into ammonia.
N2—NH4
Nitrification: Two-step process where bacteria convert
Ammonia (NH4) into Nitrite NO2. Then, NO2 is converted to
Nitrate (NO3).
NH4—NO2—NO3
Denitrification: Aerobic bacteria return N2 into the
atmosphere
Aquatic Systems
Phosphorous
Essential for formation of ATP (Adenine Triphosphate)
and DNA (Phosphates form the DNA backbone)
• Does not have an atmospheric phase (cycles
between inorganic-organic).
• Relatively scarce in the environment
• Inorganic: Rocks, minerals, and soil sediment
(reservoir)
• Organic: Erosion frees phosphorous for
assimilation
they eat plants and other animals
Nitrogen & Phosphorous Cycle
FRQ
Carbon Cycle
