Water and Carbon Cycles
Define dynamic equilibrium in the context of the water and carbon cycles.
EXAM ANSWER
Dynamic equilibrium is a state of balance within a system where the inputs and outputs are equal, despite constant movement of energy or matter. If a change occurs, the system undergoes self-regulation through feedback loops to restore the original balance.
Pro Tip: Use this term when discussing how systems respond to human interference or natural shifts in AQA ‘systems’ questions.
EASY ANSWER
It is like a busy shop where people enter and leave at the same rate; the number of people inside stays the same even though individuals are constantly moving in and out.
Describe the drainage basin as an open system.
EXAM ANSWER
A drainage basin is an open system because it has inputs (precipitation), outputs (evapotranspiration, river discharge), stores (soil moisture, groundwater), and flows (throughflow, overland flow). Matter and energy cross the system boundaries.
Pro Tip: Be prepared to draw and label a system diagram showing transfers and stores for a 4-mark question.
EASY ANSWER
It is like a kitchen sink where water comes in from the tap, stays in the bowl for a bit, and then drains out the bottom into a pipe.
Differentiate between infiltration and percolation.
EXAM ANSWER
Infiltration is the vertical movement of water from the ground surface into the soil. Percolation is the deeper vertical movement of water through the soil and into the underlying permeable rock layers or aquifers.
Pro Tip: Precision is key; examiners look for the specific distinction between soil entry (infiltration) and rock entry (percolation).
EASY ANSWER
Infiltration is like water soaking into a sponge; percolation is the water then dripping out the bottom of that sponge into a bucket below.
What is carbon sequestration?
EXAM ANSWER
Carbon sequestration is the process of capturing and long-term storage of atmospheric carbon dioxide. Methods include biological sequestration (forests and oceans absorbing CO2 via photosynthesis) and technological sequestration (Carbon Capture and Storage or CCS at power stations).
Pro Tip: Link sequestration to mitigation strategies for climate change when answering 20-mark evaluative essays.
EASY ANSWER
It is like hoovering up dust (CO2) from the air and locking it away in a safe so it can no longer float around and cause problems.
Explain a positive feedback loop within the carbon cycle.
EXAM ANSWER
A positive feedback loop is a process where an initial change triggers a sequence of events that amplifies the original change. For example, rising temperatures melt permafrost, which releases methane; as a potent greenhouse gas, methane further increases global temperatures.
Pro Tip: Always identify the ‘multiplier effect’ and the specific sequence of events when explaining positive feedback.
EASY ANSWER
It is like a snowball rolling down a hill; it gets bigger and faster the further it goes, making the original problem much worse.
Compare the roles of photosynthesis and respiration in the carbon cycle.
EXAM ANSWER
Photosynthesis is a flux that removes CO2 from the atmosphere to create glucose in plants, acting as a carbon sink. Respiration is a flux that releases CO2 back into the atmosphere as organisms break down glucose for energy, acting as a carbon source.
Pro Tip: Remember that these are considered ‘fast’ carbon cycle fluxes compared to the millions of years involved in rock formation.
EASY ANSWER
Photosynthesis is the planet ‘breathing in’ to store energy, while respiration is the planet ‘breathing out’ to use that energy.
Describe the characteristics of the ‘Slow Carbon Cycle’.
EXAM ANSWER
The slow carbon cycle involves the movement of carbon between the atmosphere, oceans, and lithosphere over millions of years. Key processes include the chemical weathering of rocks, the accumulation of marine sediment on the ocean floor, and volcanic outgassing.
Pro Tip: AQA often asks how human activity, such as fossil fuel combustion, bypasses this slow cycle by releasing millions of years of stored carbon in decades.
EASY ANSWER
This is the ‘slow lane’ where carbon gets trapped in rocks or fossil fuels for millions of years before eventually being released back into the air.
Outline the impact of deforestation on the water cycle.
EXAM ANSWER
Deforestation reduces interception and evapotranspiration. This leads to increased surface runoff, higher river discharge, and a greater risk of flooding. It also disrupts the local convectional rainfall cycle, often leading to regional drying.
Pro Tip: When discussing river regimes, mention that deforestation shortens the ‘lag time’ on a hydrograph and increases the ‘peak discharge’.
EASY ANSWER
Removing trees is like taking the lid off a box; rain hits the ground faster and runs away immediately instead of being caught by leaves and recycled into the air.