Carbon cycle
COβ β glucose via photosynthesis and respiration. Combustion + decomposition add COβ.
The cycle:
- PHOTOSYNTHESIS β plants take COβ from air, fix into glucose.
- FEEDING β animals eat plants, taking in carbon.
- RESPIRATION β all organisms break down glucose, releasing COβ.
- DECOMPOSITION β when organisms die, decomposers break them down, releasing COβ.
- FOSSILISATION β over millions of years, dead organisms become coal, oil, gas (carbon stored).
- COMBUSTION β burning fossil fuels and wood releases stored COβ rapidly.
The balance.
- Without human activity, in/out are balanced.
- HUMANS BURN fossils faster than photosynthesis can absorb β COβ rising in atmosphere β GLOBAL WARMING.
Worked qualitative. Why does deforestation make global warming worse?
- Trees absorb COβ via photosynthesis.
- Cutting trees REMOVES this COβ sink.
- BURNING the wood RELEASES the stored carbon.
- Double effect: less absorption + more release.
- Replanting trees is one strategy to mitigate.
Cambridge tip. Memorise the 6 steps. Always include both PHOTOSYNTHESIS and RESPIRATION (the main flux).
- Photosynthesis: COβ β glucose.
- Respiration: glucose β COβ.
- Decomposition releases COβ.
- Combustion (fossils, wood) β COβ.
- Fossilisation locks carbon up.