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Flip to reveal answersState the key difference between energy flow and matter cycling in ecosystems.
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All 30 Flashcards — The carbon cycle
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Question
State the key difference between energy flow and matter cycling in ecosystems.
Answer
Energy flows through ecosystems in one direction and is lost as heat. Matter is recycled repeatedly through biogeochemical cycles.
💡 Hint
Energy = one-way; Matter = cycles
Question
State where most carbon is stored in a tree.
Answer
Most carbon in a tree is stored in woody biomass, especially the trunk, branches, and roots.
💡 Hint
Wood = biggest store
Question
State two major carbon stores.
Answer
Major carbon stores include the atmosphere, living biomass, soils, oceans, and rocks/fossil fuels.
💡 Hint
Any two: atmosphere/biomass/soils/oceans/rocks
Question
Explain why burning fossil fuels increases atmospheric CO₂.
Answer
Burning fossil fuels releases carbon that was stored underground for millions of years, adding extra CO₂ to the atmosphere faster than sinks can remove it.
💡 Hint
Ancient carbon released quickly
Question
Explain why cold ocean water absorbs more CO₂ than warm water.
Answer
Cold water can hold more dissolved gas than warm water, so colder oceans absorb more CO₂ from the atmosphere.
💡 Hint
Cold water holds more gas
Question
Quick check: Which cycles in ecosystems — energy or matter?
Answer
Matter cycles; energy flows through and is lost as heat.
💡 Hint
Matter cycles; energy does not
Question
Define the biological pump.
Answer
The biological pump is the process where phytoplankton fix carbon by photosynthesis and carbon-rich material sinks to deeper water when organisms die or produce waste, storing carbon long-term.
💡 Hint
Phytoplankton → sinking carbon
Question
Define the term biogeochemical cycle.
Answer
A biogeochemical cycle is the movement of elements (matter) between living organisms and the physical environment.
💡 Hint
Elements move between biotic and abiotic parts
Question
Define carbon store.
Answer
A carbon store is a place where carbon is held for a period of time, such as the atmosphere, oceans, soils, biomass, or fossil fuels.
💡 Hint
A “storage place” for carbon
Question
State two major carbon stores and one major carbon flow.
Answer
Stores: oceans and soils (also atmosphere/biomass/rocks). Flow: photosynthesis (also respiration/decomposition/combustion).
💡 Hint
2 stores + 1 flow
Question
State one way deforestation affects the carbon cycle.
Answer
Deforestation reduces carbon uptake because fewer trees photosynthesise, and it can release stored carbon if biomass is burned or decomposes.
💡 Hint
Double effect: less uptake + more release
Question
Explain what happens to carbon when forest biomass is burned.
Answer
Combustion oxidises carbon in wood and releases it rapidly to the atmosphere as CO₂.
💡 Hint
Burning = fastest CO₂ release
Question
State two carbon flows between stores.
Answer
Key carbon flows include photosynthesis, respiration, decomposition, feeding, and combustion.
💡 Hint
Any two flows: photosynthesis/respiration/decomposition/combustion
Question
State one way carbon leaves the ocean and returns to the atmosphere.
Answer
Carbon can leave the ocean when surface water warms and releases dissolved CO₂, or during upwelling when CO₂-rich deep water rises and CO₂ escapes to the air.
💡 Hint
Warming or upwelling releases CO₂
Question
Give one farming practice that makes land a carbon source and one that helps it act as a sink.
Answer
Ploughing/disturbing soil can increase decomposition and release CO₂ (source). No-till, cover crops, or adding compost can increase soil organic matter (sink).
💡 Hint
Source vs sink farming practice
Question
Distinguish between a transfer and a transformation (give one example of each).
Answer
A transfer moves matter without changing its form (e.g., water flowing from river to ocean). A transformation changes matter into a new form (e.g., photosynthesis turning CO₂ into glucose).
💡 Hint
Transfer = move; Transformation = change form
Question
Define carbon sink using the correct “balance” wording.
Answer
A carbon sink is a store that absorbs more CO₂ than it releases over a given time period.
💡 Hint
Absorbs MORE than releases
Question
Explain how decomposition returns carbon to the atmosphere.
Answer
Decomposers break down dead organic matter and respire, releasing carbon back as CO₂, and methane may form in low-oxygen conditions.
💡 Hint
Decomposers respire carbon out
Question
Define ocean acidification (linked to carbon).
Answer
Ocean acidification is a decrease in ocean pH caused by the ocean absorbing excess atmospheric CO₂, forming carbonic acid in seawater.
💡 Hint
More CO₂ dissolved → lower pH
Question
Define carbon sink and carbon source.
Answer
A carbon sink absorbs more CO₂ than it releases. A carbon source releases more CO₂ than it absorbs.
💡 Hint
Sink = absorbs more; Source = releases more
Question
Explain why carbon in fossil fuels is considered part of a “slow” cycle.
Answer
Fossil fuel carbon can be stored for millions of years, so it moves into and out of the active cycle extremely slowly compared with carbon in living biomass.
💡 Hint
Slow = stored for millions of years
Question
Explain how ocean uptake of CO₂ can be both helpful and harmful.
Answer
Oceans absorb CO₂ and reduce the amount in the atmosphere, but dissolved CO₂ forms carbonic acid and lowers pH, harming shell-forming organisms and food webs.
💡 Hint
Sink benefit vs acidification cost
Question
State two conditions that slow decomposition and increase soil carbon storage.
Answer
Cold temperatures and waterlogged or dry conditions slow decomposition, allowing more carbon to remain in soils as organic matter.
💡 Hint
Cold + low oxygen (waterlogged) slows decay
Question
Explain why ocean absorption of CO₂ does not “solve” the problem.
Answer
Oceans absorb only part of human emissions, and increased uptake causes ocean acidification, so atmospheric CO₂ can still rise while marine ecosystems are harmed.
💡 Hint
Partial sink + side effect
Question
Exam tip: In one sentence, link photosynthesis and respiration to the carbon cycle.
Answer
Photosynthesis transfers carbon from the atmosphere into biomass, while respiration releases carbon dioxide back to the atmosphere.
💡 Hint
Two-process linkage sentence
Question
Exam tip: If a question says “stores and flows”, what must you include?
Answer
You must name at least one carbon store (e.g., atmosphere, ocean, soil) and at least one flow/process moving carbon between stores (e.g., photosynthesis, respiration).
💡 Hint
Always include BOTH
Question
Exam-ready sentence: Explain why deforestation can turn a sink into a source.
Answer
Deforestation increases atmospheric CO₂ because stored carbon is released by burning or decomposition, and fewer trees remain to absorb CO₂ by photosynthesis.
💡 Hint
Double effect: release + reduced uptake
Question
Give one example of a carbon sink and one example of a carbon source.
Answer
A growing forest is a carbon sink because photosynthesis removes CO₂ from the air. Burning fossil fuels is a carbon source because combustion releases CO₂.
💡 Hint
Example pair: growing forest vs fossil fuels
Question
Exam tip: If asked “how does CO₂ enter the ocean?”, what wording should you use?
Answer
Say CO₂ “dissolves into seawater at the surface”, rather than saying it “flows in as bubbles”.
💡 Hint
Use “dissolves” in exam answers
Question
Exam-ready chain: Explain how fossil fuels disrupt the balance of sinks and sources.
Answer
Fossil fuel combustion increases carbon sources by releasing long-term stored carbon, so atmospheric CO₂ rises because natural sinks cannot absorb the extra carbon fast enough.
💡 Hint
Source increases faster than sink uptake
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Topic 2.7 hub
Biogeochemical cycles
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