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Guiding question

• How do human activities affect nutrient cycling, and what impact does this have on the sustainability of environmental systems?

SL and HL knowledge statements

2.3.1 Biogeochemical cycles ensure chemical elements continue to be available to living organisms.

2.3.2 Biogeochemical cycles have stores, sinks and sources.

2.3.3 Organisms, crude oil and natural gas contain organic stores of carbon. Inorganic stores can be found in the atmosphere, soils and oceans.

2.3.4 Carbon flows between stores in ecosystems by photosynthesis, feeding, defecation, cellular respiration, death and decomposition.

2.3.5 Carbon sequestration is the process of capturing gaseous and atmospheric carbon dioxide and storing it in a solid or liquid form.

2.3.6 Ecosystems can act as stores, sinks or sources of carbon.

2.3.7 Fossil fuels are stores of carbon with unlimited residence times. They were formed when ecosystems acted as carbon sinks in past eras and become carbon sources when burned.

2.3.8 Agricultural systems can act as carbon stores, sources and sinks, depending on the techniques used.

2.3.9 Carbon dioxide is absorbed into the oceans by dissolving and is released as a gas when it comes out of a solution.

2.3.10 Increases in concentrations of dissolved carbon dioxide cause ocean acidification, harming marine animals.

2.3.11 Measures are required to alleviate the effects of human activities on the carbon cycle.

Knowledge statements for HL only

2.3.12 The lithosphere contains carbon stores in fossil fuels and in rocks, such as limestone, that contain calcium carbonate.

2.3.13 Reef-building corals and molluscs have hard parts that contain calcium carbonate that can become fossilized in limestone.

2.3.14 In past geological eras, organic matter from partially decomposed plants became fossilized in coal, and partially decomposed marine organisms became fossilized in oil and natural gas held in porous rocks.

2.3.15 Methane is produced from dead organic matter in anaerobic conditions by methanogenic bacteria.

2.3.16 Methane has a residence time of about 10 years in the atmosphere and is eventually oxidized to carbon dioxide.

2.3.17 The nitrogen cycle contains organic and inorganic stores.

2.3.18 Bacteria have essential roles in the nitrogen cycle.

2.3.19 Denitrification only happens in anaerobic conditions, such as soils that are waterlogged.

2.3.20 Plants cannot fix nitrogen so atmospheric dinitrogen (N₂) is unavailable to them unless they form mutualistic associations with nitrogen-fixing bacteria.

2.3.21 Flows in the nitrogen cycle include mineral uptake by producers, photosynthesis, consumption, excretion, death, decomposition and ammonification.

2.3.22 Human activities such as deforestation, agriculture, aquaculture and urbanization change the nitrogen cycle.

2.3.23 The Haber process is an industrial process that produces ammonia from nitrogen and hydrogen for use as fertilizer.

2.3.24 Increases in nitrates in the biosphere from human activities have led to the planetary boundary for the nitrogen cycle being crossed, making irreversible changes to Earth systems likely.

2.3.25 Global collaboration is needed to address the uncontrolled use of nitrogen in industrial and agricultural processes and bring the nitrogen cycle back within planetary boundaries.

Practical activities

1. 2.3.4 Application of skills: Create a systems diagram of the carbon cycle.
2. 2.3.17 HL Application of skills: Create a systems diagram of the nitrogen cycle.
3. More practical activities coming soon.

Possible engagement opportunities

Design a plan to make these into CAS activities:

• Provide advocacy about the use of organic, instead of inorganic, fertilizers around school or community green areas.

• Explore issues of justice for local communities when the local environment is overexploited for financial gain.

Happy learning!