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Nutrient Cycles
In this presentation you will: Identify the stages of the carbon and nitrogen cycles Investigate the causes of rising carbon dioxide levels Explore the impact of the over-use of nitrogen based fertilizers
ClassAct SRS enabled.
Nutrient Cycles
Nutrient cycles summarize the movement of certain elements through ecosystems.
In this presentation you will study the carbon and nitrogen cycles. You will identify the different stages of these cycles and investigate their importance. You will also investigate how human activity can disturb the natural balance of these cycles and cause pollution.
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Nutrient Cycles
Nutrient cycles summarize the movement of certain elements through ecosystems.
Elements may be combined to form complex organic molecules. These later decompose to form simpler organic and inorganic molecules.
Nutrient Cycles
These simpler molecules can be used again to become incorporated into living things. This is called the cycling pool.
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Nutrient Cycles
Upsetting the Balance
As well as the cycling pool of an element, all cycles have a larger reservoir pool. This is usually abiotic, that is, not made up of living things.
Exchanges between the reservoir and the biotic cycling pools usually happen slowly.
Human activity often speeds up the movement of molecules through the cycles. This may upset the natural balance, cause build up of substances at one point and cause pollution.
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Nutrient Cycles
1
Which part of a nutrient cycle involves living organisms?
Question
A) The cycling pool
B) The reservoir pool
C) Both the cycling and the reservoir pool
D) Neither the cycling nor the reservoir pool
Nutrient Cycles
The Carbon Cycle – An Overview
CO2 in atmospherePhotosynthesis
Photosynthesis
Respiration
Death
C in detritus
Detrivores,Decomposers
C in humus
Animals
Combustion
CO2 in water (HCO3
- ions)
C in algae
Death
Respiration by detrivores and decomposers
Respiration Animals
Death,Excretion
Death,Excretion
Diffusion
C in detritusFossil fuels eg coal, oil
Flow of carbon in thousands of Tg/year
Tg = Terragram1 Tg = 1 million metric tons
1 metric ton = 1000kg
Rocks in the Earth
C = Carbon HCO3- = Hydrogen Carbonate
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Nutrient Cycles
There are 4 large reservoirs of carbon:the atmosphere, the oceans, limestone rocks and fossil fuels.
Photosynthesis
Photosynthesis
Respiration
Death
C in detritus
Detrivores,Decomposers
C in humus
Animals
Combustion
CO2 in water (HCO3 - ions)
C in algae
Death
Respiration by detrivores and decomposers
Respiration Animals
Death,Excretion
Death,Excretion
Diffusion
C in detritusFossil fuels eg coal, oil
Flow of carbon in thousands of Tg/year
Tg = Terragram1 Tg = 1 million metric tons
1 metric ton = 1000kg
Rocks in the Earth
CO2 in atmosphere
CO2 in water (HCO3
- ions)
Rocks in the Earth
Fossil fuels eg coal, oil Next >
Nutrient Cycles
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The processes that put carbon dioxide into the atmosphere are:respiration, combustion and diffusion.
CO2 in atmospherePhotosynthesis
Photosynthesis
Respiration
Death
C in detritus
Detrivores,Decomposers
C in humus
Animals
Combustion
CO2 in water (HCO3
- ions)
C in algae
Death
Respiration by detrivores and decomposers
Respiration Animals
Death,Excretion
Death,Excretion
Diffusion
C in detritusFossil fuels eg coal, oil
Flow of carbon in thousands of Tg/year
Tg = Terragram1 Tg = 1 million metric tons
1 metric ton = 1000kg
Rocks in the Earth
Respiration
Combustion
Diffusion
RespirationRespiration
Nutrient Cycles
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The processes that remove carbon dioxide from the atmosphere are:photosynthesis and diffusion.
CO2 in atmospherePhotosynthesis
Photosynthesis
Respiration
Death
C in detritus
Detrivores,Decomposers
C in humus
Animals
Combustion
CO2 in water (HCO3
- ions)
C in algae
Death
Respiration by detrivores and decomposers
Respiration Animals
Death,Excretion
Death,Excretion
Diffusion
C in detritusFossil fuels eg coal, oil
Flow of carbon in thousands of Tg/year
TG = Terra Ton1 Tg = 1 million metric tons
1 metric ton = 1000kg
Rocks in the Earth
Photosynthesis
Diffusion
Nutrient Cycles
2
Which of the following processes does not put carbon dioxide back into the atmosphere?
Question
A) Photosynthesis
B) Combustion
C) Respiration
D) Decomposition
Nutrient Cycles
There is a balance between the carbon (in carbon dioxide) stored in the atmosphere and the amount of carbon (in hydrogen carbonate ions) stored in the sea.
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There is also a fine balance between the amount of carbon dioxide removed from the air by photosynthesis and the amount replaced by respiration.
The Carbon Dioxide Balance
Nutrient Cycles
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Despite the fact that these processes maintain a natural balance, the level of carbon dioxide in the atmosphere is still rising.
This is because the burning of fossil fuels and wood releases carbon dioxide into the atmosphere.
Upsetting the CO2 Balance
In addition to this, deforestation removes large areas of trees that would have absorbed large quantities of carbon dioxide for photosynthesis.
Nutrient Cycles
3
Why does deforestation result in increased carbon dioxide levels in the atmosphere?
Question
A) It results in fewer trees taking up nutrients from the soil
B) It results in fewer trees being burnt
C) It results in fewer trees respiring
D) It results in fewer trees photosynthesizing
Nutrient Cycles
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Around 1850, the atmosphere contained about 270ppm (parts per million) of carbon dioxide. In 2004, it contained around 360 ppm, and is rising at a rate of 1 to 2 ppm per year.
The worst possible long term effect of increasing carbon dioxide levels in the atmosphere is the 'greenhouse effect', which in turn leads to global warming.
The Greenhouse Effect and Global Warming
Time (Years)A
tmo
sp
he
ric
CO
2 l
ev
els
(p
pm
)
Nutrient Cycles
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The atmosphere is made up of 79% nitrogen. A shortage of nitrogen based compounds in ecosystems can reduce plant growth, and animal growth.
The Nitrogen Cycle – An Overview
Nutrient Cycles
The abiotic outer cycle consists of nitrogen from the air being 'fixed' by:
NO3- NH4
+
NO2-
Leaching to ground water
Bacteria
Nitrification = oxidation of ammonium to nitrate
toxic
Nitrogen fixation by lightning
Nitrogen in plantse.g. protein
Uptake of nitratesand ammonium
Nitrogen in animalse.g. Protein
Feeding
Nitrogen in detritus and humus
e.g. as protein
Microorganisms:Bacteria and fungi
Invertebrates
Nitrogen gases in atmosphere
Death andexcretion
Fertilizer manufacture(Nitrogen fixation by
Haber-Bosch process)
NO3-, NH4
+
Denitrification: denitrifying bacteria
Free-living bacteria
Bacteria in legume
root nodules
Nitrogen Fixation
lightning
Nitrogen fixation by lightning
and the Haber-Bosch process.
Fertilizer manufacture(Nitrogen fixation by
Haber-Bosch process)
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Nutrient Cycles
Nitrogen can also be fixed by bacteria in the root nodules of legumes and by bacteria living freely in the soil.
NO3- NH4
+
NO2-
Leaching to ground water
Bacteria
Nitrification = oxidation of ammonium to nitrate
toxic
Nitrogen fixation by lightning
Nitrogen in plantse.g. protein
Uptake of nitratesand ammonium
Nitrogen in animalse.g. Protein
Feeding
Nitrogen in detritus and humus
e.g. as protein
Microorganisms:Bacteria and fungi
Invertebrates
Nitrogen gases in atmosphere
Death andexcretion
Fertilizer manufacture(Nitrogen fixation by
Haber-Bosch process)
Denitrification: denitrifying bacteria
Free-living bacteria
Bacteria in legume
root nodules
Nitrogen Fixation
NO3-, NH4
+
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Nutrient Cycles
Leguminous Plants
Leguminous plants are plants that produce peas or beans. They contain nodules on their roots that are full of nitrogen fixing bacteria.
Farmers often rotate crop plants with leguminous (pea or bean) plants. This is because crop plants take nitrogen from the soil and leguminous plants put nitrogen back into the soil.
Root nodule
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Nutrient Cycles
Rhizobium
One of the most common bacteria that produce nodules on legumes is Rhizobium. The relationship between the bacterium and the plant is mutualistic, that is, both organisms benefit.
The plant obtains some nitrogen from the bacterium and the bacterium obtains other nutrients, in particular, sugars, made by the plant.
Rhizobium bacterium
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Nutrient Cycles
In the central cycle, plants absorb nitrates or ammonium ions from the soil.
NO3- NH4
+
NO2-
Leaching to ground water
Bacteria
Nitrification = oxidation of ammonium to nitrate
toxic
Nitrogen fixation by lightning
Nitrogen in plantse.g. protein
Uptake of nitratesand ammonium
Nitrogen in animalse.g. Protein
Feeding
Nitrogen in detritusand humus
e.g. as protein
Microorganisms:Bacteria and fungi
Invertebrates
Nitrogen gases in atmosphere
Death andexcretion
Fertilizer manufacture(Nitrogen fixation by
Haber-Bosch process)
NO3-, NH4
+
Denitrification: denitrifying bacteria
Free-living bacteria
Bacteria in legume
root nodules
Nitrogen Fixation
Nitrogen in plantse.g. protein
The nitrogen forms amino acids and proteins.
Uptake of nitratesand ammonium
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Nutrient Cycles
These compounds may or may not be eaten by animals.
NO3- NH4+
Leaching to ground water
Bacteria
Nitrification = oxidation of ammonium to nitrate
toxic
Nitrogen fixation by lightning
Nitrogen in plantse.g. protein
Uptake of nitratesand ammonium
Nitrogen in animalse.g. Protein
Feeding
Nitrogen in detritusand humus
e.g. as protein
Microorganisms:Bacteria and fungi
Invertebrates
Nitrogen gases in atmosphere
Death andexcretion
Fertilizer manufacture(Nitrogen fixation by
Haber-Bosch process)
Denitrification: denitrifying bacteria
Free-living bacteria
Bacteria in legume
root nodules
Nitrogen Fixation
Nitrogen in animalse.g. Protein
However, they are all eventually turned into detritus (rotting organic matter).
Death andexcretion
Nitrogen in detritusand humus
e.g. as protein
NO3-, NH4
+NO2-
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Nutrient Cycles
Detritus is attacked by detrivores and decomposers.
NO3- NH4+
NO2-
Leaching to ground water
Bacteria
Nitrification = oxidation of ammonium to nitrate
toxic
Nitrogen fixation by lightning
Nitrogen in plantse.g. protein
Uptake of nitratesand ammonium
Nitrogen in animalse.g. Protein
Feeding
Nitrogen in detritusand humus
e.g. as protein
Microorganisms:Bacteria and fungi
Invertebrates
Nitrogen gases in atmosphere
Death andexcretion
Fertilizer manufacture(Nitrogen fixation by
Haber-Bosch process)
Denitrification: denitrifying bacteria
Free-living bacteria
Bacteria in legume
root nodules
Nitrogen Fixation
NH4+
Invertebrates
Microorganisms:Bacteria and fungi
NO3-
The nitrogen is released as ammonium ions that are converted to nitrates.
NO3-, NH4
+NO2-
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Nutrient Cycles
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The conversion of ammonium ions to nitrites and then to nitrates is known as nitrification.
The bacteria that carry out nitrification are called nitrifying bacteria. They are chemoautotrophic, that is, they obtain their energy from oxidation of inorganic ions.
Nitrification
Nitrification = oxidation of ammonium to nitrate
NO3- NH4+
Bacteria
NO2-
toxic
Nutrient Cycles
4
Nitrogen fixing bacteria put nitrogen back into the soil.
Answer True or False.
Question
Nutrient Cycles
5
Nitrification is:
Question
A) The conversion of ammonium to nitrite
B) The conversion of nitrate to nitrite
C) The conversion of ammonium to nitrate
D) The conversion of nitrite to nitrate
Nutrient Cycles
Most nitrogen-based fertilizers are made by the Haber-Bosch process. This accounts for about one third of the total nitrogen fixation each year.
Normally, natural nitrogen fixation would be balanced by denitrification. This is the process whereby bacteria take up inorganic nitrogen compounds and release nitrogen gas into the atmosphere.
However, because there is more nitrogen being put into the soil than put back into the atmosphere, by the use of fertilizers, the balance is being disrupted.
Upsetting the Nitrogen Balance
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Nutrient Cycles
6
Which of the following does not put nitrogen back into the ground?
Question
A) Lightning
B) Denitrification
C) Nitrification
D) The Haber-Bosch process
Nutrient Cycles
7
Which of the following is the most harmful way of putting nitrogen back into ecosystems?
Question
A) Lightning
B) The Haber-Bosch process
C) Nitrogen fixing bacteria
D) Death and excretion
Nutrient Cycles
Nitrogen-based fertilizers lead to a type of pollution called eutrophication. The nitrates are washed by rainfall into ground water streams. Water supplies become enriched with nitrates.
As a result of eutrophication, the algae at the water's edge grow rapidly. They prevent light from reaching aquatic plants.
Eutrophication
These plants, and the invertebrates that feed on them, then die. The algae also block water supplies, including drinking water.
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Nutrient Cycles
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When the algae die, plants and invertebrates die and they are decomposed by bacteria. These bacteria deoxygenate, that is, remove oxygen from, the water. This is known as hypoxia.
Hypoxia
The bacteria also produce hydrogen sulphide gas, which is toxic.
The fish and invertebrates that require high levels of oxygen die. This affects food webs and subsequently the entire ecosystem.
Nutrient Cycles
8
Which of the following is likely to be the best long-term solution for the problem of eutrophication?
Question
A) Re-stocking water systems with fish and invertebrates
B) Removing pond weed and algae from water systems
C) Supplying people with free bottled water
D) Reducing the use of artificial fertilizers
Nutrient Cycles
Summary
Identify the stages of the nitrogen cycle
After completing this presentation you should be able to:
Identify the stages of the carbon cycle
Show knowledge of the causes of increasing carbon dioxide levels
Show knowledge and understanding of the consequences of the over-use of nitrogen based fertilizers
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