2. Geochemical Cycles
Geochemical cycles represent the movement of a particular form of matter through the living and nonliving parts of an ecosystem.
The 3 main cycles that we will study are:
Water (Hydrologic)
Carbon
Nitrogen
Since matter can neither be created nor destroyed, and Earth is a closed system, these essential nutrients must be continuously cycled.

3. The Water Cycle
The chemical formula of water is H2O, and this is necessary for the life processes of all living things.
Water is found in…
Earth’s surface (including oceans, lakes, rivers, etc.)
97% is in the ocean!
Of the 3% that is freshwater, 2% is frozen in glaciers
Under Earth’s surfaces (groundwater, aquifers)
In the atmosphere
In living organisms

4. The Water Cycle
This cycle is driven by the sun, which causes evaporation from reservoirs and organisms.
Image: © Airs by Nasa

5. The Water Cycle The main stages include:
Precipitation: water falls to Earth as a liquid (usually rain, sleet or snow)
Runoff: liquid water that isn’t infiltrated runs along the surface and collects in puddles, lakes, oceans, or other bodies of water.
Infiltration: some water seeps from the surface of the Earth to underground aquifers
Image: © Airs by Nasa

6. The Water Cycle The main stages include:
Evaporation: sun heats liquid water to vapor and it rises to the atmosphere
Transpiration: water rises back into the atmosphere as water vapor from plants
Condensation: water condenses to form clouds before precipitating again
Image: © Airs by Nasa

7. Living Organisms and the Water Cycle
All organisms take in water for nutrient transport, chemical reactions, diffusion, etc.
Which means, they also have to eliminate water too (urine/feces)
All organisms release water when breaking down food for energy (cellular respiration)
C6H12O6 + 6O2  6CO2 + 6H2O + ATP
Plants take in water to make sugar (photosynthesis)
6CO2 + 6H2O  C6H12O6 + 6O2
Teaching Tip: Students may wonder why photosynthesis, respiration, elimination, etc. are not main steps of the water cycle. Remind them that the main 6 stages of the water cycle are the ones that have the biggest impact on water cycling, but these small impacts still happen!

8. Think about it…
What about human participation in the water cycle? How do we contribute to the cycle as living organisms? How do we negatively impact the cycle?
Negative Human Impact:
Deforestation: transpiration
Paving/Building/Development: Runoff and Infiltration
Pollution
Teaching Tip: Have them Think-Pair-Share before you tell them some of the answers on the slide!

9. The Carbon Cycle
Carbon is another molecule necessary for life to exist.
Carbon is found in…
Macromolecules, which are large molecules necessary for life.
Proteins (muscle, skin, etc…)
Carbohydrates (food, sugars)
Lipids (fats)
Nucleic acids (DNA and RNA)

10. The Carbon Cycle Carbon is found in… Our atmosphere (as CO2)
Minerals and rocks
Fossil fuels (coal, oil, natural gas)
Organic (living) materials in soil or aquatic sediments
Note: Carbon changes forms as it cycles, unlike water, which is always H2O
Ex. Carbon is CO2 in the atmosphere, but C6H12O6 as glucose in plants

11. The Carbon Cycle The main stages include:
Photosynthesis: plants capture CO2 from the atmosphere and use it to make sugar
Cellular Respiration: CO2 released into atmosphere as waste from metabolism
Consumption: one organism eats another for carbon
Image © Airs

12. The Carbon Cycle The main stages include:
Combustion: CO2 released into atmosphere from burning
Decomposition: decomposers break down carbon from dead organisms, allowing it to be recycled in the soil
Fossilization: converts carbon from once-living organisms into a fuel source through intense heat and compression, including natural gas, oil, and coal (fossil fuels)
Image © Airs

13. Living Organisms and the Carbon Cycle
Decomposers (like bacteria and fungi) break down dead materials and return the nutrients (like Carbon) to the soil
Photosynthetic organisms (like plants and algae) remove CO2 from the atmosphere and convert it into simple sugars.
Animals, plants and fungi do cellular respiration in order to break down carbon-rich foods for energy

14. Think about it…
What about human participation in the carbon cycle? How do we contribute to the cycle as living organisms? How do we negatively impact the cycle?
Negative Human Impact:
Combustion: when wood or fossil fuels, which contain carbon, are burned  causing major of CO2 in the atmosphere
Teaching Tip: Have them Think-Pair-Share before you tell them some of the answers on the slide!

15. The Nitrogen Cycle
Nitrogen is the last molecule necessary for life to exist that we will focus on.
Nitrogen is found in…
Two Macromolecules: Proteins and Nucleic acids
In the atmosphere in the form of a gas - N2 (elemental nitrogen)
Note: Plants and animals can NOT use nitrogen in this form!!
Fossil fuels
Waste
Soil

16. The Nitrogen Cycle The main stages include:
Nitrogen fixation: Bacteria (or lightning!) in the soil or water convert nitrogen (from the air or water) into forms that plants can use
Image © sfbaywalk

17. The Nitrogen Cycle The main stages include:
Decomposition: decomposers like bacteria break dead matter down, returning nitrogen to the soil.
Image © sfbaywalk

18. The Nitrogen Cycle The main stages include:
Ammonification: Bacteria convert nitrogen from waste (urine and feces) into ammonia.
Image © sfbaywalk

19. The Nitrogen Cycle The main stages include:
Nitrification: Bacteria convert nitrogen in ammonia into nitrates and nitrites to be absorbed by plants in their roots.
This is how nitrogen enters the food chain, and eventually reaches us.
Image © sfbaywalk

20. The Nitrogen Cycle The main stages include:
Denitrification: bacteria convert nitrogen in ammonia to N2 so it can go back into the atmosphere
Image © sfbaywalk

21. Living Organisms and the Nitrogen Cycle
The nitrogen cycle is different from other geochemical cycles, in that no step is completed without the help of living organisms.
Bacteria is most important living organism in converting nitrogen to different forms.
Fungi and other decomposers breakdown nitrogen-rich waste and put it in the soil

22. Think about it…
What about human participation in the nitrogen cycle? How do we contribute to the cycle as living organisms? How do we negatively impact the cycle?
Negative Human Impact:
Fertilizers: The use of fertilizers adds WAY too much nitrogen to the soil, creating an imbalance
This excess nitrogen can get into groundwater which can be dangerous to drink
Combustion: not as major of an impact on the nitrogen cycle as the carbon cycle, but burning fossil fuels does release excess nitrogen into the atmosphere
Teaching Tip: Have them Think-Pair-Share before you tell them some of the answers on the slide!