Choose an exam and explore concepts through visual explanations, topic maps and revision checks. Open the full chapter notes whenever you need more detail.
THE VISUAL LEARNING STUDIO
See the idea. Understand the connection.
35 visual explanations across 29 chapters, with topic maps throughout the library.
The chapter index will grow as additional notes are prepared. Chapters shown here are a learning collection, not a claim that the entire exam syllabus is complete.
SEE IT. CONNECT IT. EXPLAIN IT.
Understand the chapter visually
1 visual explanation · Study the connections, then test yourself.
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FOLLOW THE PROCESS
Nitrogen: follow the transformations
1
Atmospheric N₂ → fixed nitrogen
Biological fixation converts N₂ to ammonia/ammonium forms; fixation is not nitrification.
2
Ammonium → nitrite → nitrate
Nitrification is oxidation carried out by microorganisms.
3
Plant assimilation
Plants incorporate absorbed nitrogen into organic molecules.
4
Organic nitrogen → ammonium
Ammonification returns reduced inorganic nitrogen during decomposition.
5
Nitrate → N₂
Denitrification returns nitrogen to the atmosphere under suitable conditions.
The connection These are connected pathways, not a single compulsory route for every nitrogen atom.
Exam trap Plants do not generally assimilate atmospheric N₂ directly; symbiotic microbes carry out fixation.
Which process converts ammonium to nitrite and nitrate?
Nitrification; it is distinct from nitrogen fixation and ammonification.
Study the expanded notes and the credited detailed textbook lessons. The current chapter index covers core topics; it is not a claim of exhaustive coverage of every examination syllabus. Check the official syllabus and primary references.
Biogeochemical Cycles — lesson overview
Matter moves between reservoirs
Biogeochemical cycles describe movement of elements among organisms, air, water, soils and rocks through biological, chemical and physical processes.
Unlike energy flow, matter can be recycled, but reservoirs and transfer rates differ; not every element circulates at the same speed.
A reservoir stores material; a flux is a transfer per unit time. Confusing them obscures how a system changes.
Carbon and nitrogen
Photosynthesis incorporates carbon into organic matter; respiration, decomposition and combustion can return carbon dioxide to the atmosphere.
Nitrogen fixation converts atmospheric nitrogen into biologically usable forms through particular processes; most plants do not directly use atmospheric N₂.
Ammonification releases ammonium from organic nitrogen; nitrification oxidises ammonium through nitrite to nitrate; denitrification can return nitrogen to gaseous forms.
Human influence
Fossil-fuel combustion and land-use changes alter carbon transfers; fertiliser use and combustion can alter nitrogen flows.
Adding nutrients can stimulate growth, but excess nutrient loading can contribute to eutrophication and oxygen depletion in waters.
Cycle analysis connects a local event with upstream inputs, biological transformations and downstream consequences.
