Biogeochemical cycles and ecological imbalances: From Nodule to Glacier

In the paper

Unit 3 carries 4 of the 40 botany marks; with three chapters sharing them, this one averages a little over one mark (MEC publishes weights by unit, not by chapter). The MEC scope line reads: "Biogeochemical cycles and ecological imbalances: Carbon cycle, Nitrogen cycle, Greenhouse effect, Acid rain, Ozone layer depletion, Climate change." Expect:

• Recall — the bacterium for each nitrogen step, the size of a Dobson unit, the year of the Montreal Protocol.
• Understanding — why an active nodule is pink, why the ozone hole opens in the Antarctic spring, why a waterlogged field loses nitrate.
• Application — a soil or leaf observation to explain, a gas to rank by warming power, a glacier or temperature figure to read.

Smog, eutrophication and biomagnification are in the Zoology note Environmental pollution. A biogeochemical cycle moves an element between organisms and the rocks, soil, water and air. Gaseous cycles (carbon, nitrogen) keep their reservoir in air or ocean and recover quickly; sedimentary cycles (phosphorus, sulphur) keep it in rock and run slowly.