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Science 10: Carbon, Nitrogen and Phosphorus Cycles
Goal: to become familiar with these diagrams and come to understand the flow of the carbon, nitrogen and phosphorus
through our world.
Carbon cycle
1. Choose 4 different colours
2. Make a legend and colour the arrows, boxes or circles according to the legend.
 Colour #1 – carbon stores
 Colour #2 – carbon exchanges
 Colour #3 – How carbon gets into the atmosphere
 Colour #4 – How carbon get out of the atmosphere
Answer the following questions:
1. How many kilograms are in a gigatonne?
1 000 000 000 000 kg
2. In what form is carbon released into the atmosphere? CO2
3. What is photosynthesis? Where does it occur?
photosynthesis – chloroplasts in plants (producers) convert light energy from sun -> chemical energy
(a) Write the equation for photosynthesis.
6CO2(g) + 6H2O + energy -> C6H12O6 + 6O2
(b) Does photosynthesis use or release carbon?
uses C
4. What is cellular respiration Where does it occur?
cellular respiration – plants (producers) and animals (consumers) and decomposers use sugar for energy
(a) Write the equation for cellular respiration.
C6H12O6 + 6O2  6CO2(g) + 6H2O + energy
(b) Does cellular respiration use or release carbon?
releases C
5. What is decomposition – where does the carbon go during decomposition?
decomposition – break down carbs and return C to soil or water
6. Define carbon sink/store: store and release C – absorb more C than release
(a) where would carbon be stored in the short term? (there should be four)
Land: terrestrial vegetation, organic matter in soil
Ocean: dissolved organic C, marine life
(b) where would carbon be stored in the long term? (there should be five)
Atmosphere, intermediate and deep water, marine sediments and sedimentary rock, oil and gas deposits,
coal
7. List the sources that release carbon into the atmosphere (there should be five).
cellular respiration, plant growth and decay, fossil fuel combustion, change in land use, marine life, circulation of
intermediate and deep water, volcanic eruption
8 What is the main cause of increased carbon in the atmosphere?
human activity – burning of fossil fuels, cutting and burning forests
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Nitrogen cycle
1. Choose 4 different colours
2. Make a legend and colour the arrows, boxes or circles according to the legend.
 Colour #1 – How nitrogen gets into the soil
 Colour #2 – How nitrogen gets into the plants
 Colour #3 – How nitrogen gets into the water
 Colour #4 – How nitrogen gets into the air
Answer the following questions:
1. List the 8 chemicals that contain nitrogen (include their name and formula):
N2 = nitrogen, NH3 = ammonia, NH4+ = ammonium ion, NO = nitrogen monoxide, NO2 = nitrogen dioxide, NO2- =
nitrite ion NO3- = nitrate ion
2. Explain the process of nitrogen fixation.
Nitrogen is “fixed”= combined with hydrogen to form NH3,. Then, the NH3, dissolves in water and become NH4+.
NH4+ is then used by plants.
(a) What are the two biological methods of nitrogen fixation? What do nitrogen fixing bacteria do?
1- nitrogen-fixing bacteria in soil and roots of certain plants (legumes) -> symbiotic mutualistic
relationship
2 – cyanobacteria in lichens and aquatic ecosystems
(b) What is the non-biological method of nitrogen-fixation?
lightning and cosmic radiation – much smaller quantities than bo
3. Explain the process of nitrification. What two reactions do nitrifying bacteria help with?
Production of NH4+ from NO3- in 2 steps by nitrifying bacteria NH4+  NO2-  NO3-plants need a combo of NH4+ and NO3- for optimal growth
4. Explain the process of denitrification.
Return of nitrogen to atm by denitrifying (anaerobic) bacteria NO3-  N2
5. List four ways in which nitrogen gets into the atmosphere.
1- NO and NO2 from transportatio and industry
2- NH3 conversion to gas from plants
3- NH3 from volcanic ash
4- N2 from denitrification
5- NO3- from atm-ic fixation
6. List four ways in which nitrogen gets into the soil.
1- sedimentation
2- decaying plant and animal waste
3- nitrogen fixation
4- fertilizer application
7. List three ways in which nitrogen gets into water.
1- atmospheric fixation
2- leaching and runoff (sewage and fertilizers)
3- uptake by plants from soil
8. List two sources of nitrogen for plants.
1- NH4+ nitrogen fixing bacteria in root nodules of legumes
2- NH4+ and NO3- uptake from soil (from denitrifying bacteria)
9. How does nitrogen get into animals?
Consumption of plants
10. Look up the term eutrophication. What is it? What happens?
Increased amounts of nitrogen in lakes and streams can cause eutrophication = excess nutrients cause and
increase in plant production and decay. This increase in nitrogen causes algae to grow very quickly, using up all
the oxygen, and blocking sunlight so no plants and animals can grow!
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Phosphorus cycle
1. Choose 6 different colours
2. Make a legend and colour the arrows, boxes or circles according to the legend.
 Colour #1 – Phosphorus flows
 Colour #2 – Phosphorus stores
 Colour #3 – Long cycle - How phosphorus moves from ocean sediments to soil
 Colour #4 – Short cycle – How phosphorus moves through a land ecosystem
 Colour #5 – Short cycle – How phosphorus moves through an aquatic ecosystem
 Colour #6 – Short cycles – How phosphorus moves between the land and water ecosystems
Answer the following questions:
1. List the five phosphorus sinks/stores.
Ocean sediments, Earth’s crust, mineable phosphate, terrestrial organisms, marine life
(a) Which one is the greatest?
Earth’s crust
(b) Where is phosphorus NOT stored?
Atm
2. In what form is phosphorus stored?
PO43- ions
3. List the eight main sources of phosphorus. Which one is the greatest?
Guano bird islands, industrial waste, weathering, fish harvest, fertilizers, leaching into soil, uptake by terrestrial
organisms, dissolving from sediment into water (greatest)
4. Describe the three short cycles on the diagram – one on land, one in the water and one in water/land and air. What is
the source of the phosphorus in each case?
Land:
Producers uptake phosphate from the soil, consumers eat producers and consumers that contain phosphates, then
the biota die and phosphate is returned to the soil through decomposition.
Water:
Dissolved phosphate in waterways
Water/land and air:
Runoff and leaching
5. The long cycle ties into the three short cycles. How is the long cycle different from the short cycles?
Long cycle is due to geologic uplift. Abiotic and biotic. Connects all three cycles
6. What is the main way in which humans add phosphorus to ecosystems?
fertilizers, waste and detergents
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