OCR A-Level Geography Earth's Life Support Systems: water, carbon and the management of the cycles

What Earth's Life Support Systems actually demands

Earth's Life Support Systems is the second topic of Component 1 and forms Section B of Paper 01. OCR tests the water cycle and the carbon cycle as systems of stores and fluxes, your ability to apply that systems thinking to two contrasting ecosystems, and the management of the cycles in a changing climate. The unifying skill is the same as in Landscape Systems: treat each cycle as a system, and explain change through shifts in its stores and flows.

This guide walks through each cycle, the contrasting case studies, the consequences of change and the management strand, then the exam patterns OCR repeats. Each topic has a matching dot-point page with worked exam questions; this overview ties them together.

The water cycle

The water cycle is a closed system globally (a fixed volume of water redistributed between oceans, cryosphere, groundwater, soil, atmosphere and biosphere) within which the drainage basin is the key open sub-system. Its single input is precipitation; its stores are interception, soil moisture, groundwater and channel storage; its flows are infiltration, throughflow, overland flow and baseflow; and its outputs are evapotranspiration and discharge. The water balance ($P = Q + E \pm \Delta S$) ties them together, and natural and human factors (deforestation, urbanisation, abstraction) change the stores and flows.

The carbon cycle

The carbon cycle is also a closed global system of stores and fluxes. The fast (biological) cycle exchanges carbon between atmosphere, biosphere, soil and surface ocean over days to centuries; the slow (geological) cycle moves it between rocks, the deep ocean and the atmosphere over millions of years. Sequestration locks carbon away short term (biomass, soil) and long term (rock, deep ocean), and human activity, by burning fossil fuels and clearing forests, transfers slow-cycle carbon into the fast cycle and disrupts the balance.

Contrasting case studies: rainforest and tundra

The two named case studies show the cycles at opposite extremes. The tropical rainforest runs both cycles fast, recycling water through evapotranspiration and storing carbon in living biomass, with deforestation as the key disruptor. The Arctic tundra runs them slowly, locking water and a huge carbon store in permafrost, with warming and thaw as the key disruptor. Comparing them is a favourite exam route.

Consequences and management

Managing the carbon cycle and climate covers the consequences of rising carbon (warming, ocean acidification, sea-level rise, ecosystem stress and feedbacks) and the management response: mitigation (cutting the cause) and adaptation (managing the consequences), from international agreements through national policy to local sink enhancement.

How Earth's Life Support Systems is examined

A typical OCR profile for Section B of Paper 01:

• Data-response and resource questions. Reading hydrographs, climate graphs, flux diagrams and tables, and describing patterns (AO3).
• Process explanation. Explaining stores and flows and how vegetation links the water and carbon cycles.
• Calculation. Water balance and carbon flux figures, with interrogation of assumptions (AO3).
• Extended essay. A 16-mark question rewarding evaluation, for example assessing human disruption of the cycles or managing the carbon cycle across scales.

Check your knowledge

A mix of recall and application questions covering Earth's Life Support Systems. Attempt them, then check against the solutions.

1. Is the global water cycle open or closed? Justify your answer. (2 marks)
2. State the water balance equation. (2 marks)
3. Name three stores within a drainage basin. (3 marks)
4. Distinguish between the fast and slow carbon cycles. (2 marks)
5. Explain why rainforest soils store little carbon. (2 marks)
6. Explain why the tundra stores so much carbon despite low productivity. (2 marks)
7. Define ocean acidification. (2 marks)
8. Distinguish between mitigation and adaptation. (2 marks)