Syllabus concepts to know

• 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.
• 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.
• 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.
• 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 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.