# The Carbon and Water Cycles
Materials are constantly recycled in nature. The carbon and water cycles show how these essential substances move through living organisms and the environment.
1. The Carbon Cycle
Carbon enters the atmosphere as CO₂:
- Respiration (all organisms)
- Combustion (burning fossil fuels and wood)
- Decomposition (decomposers respire)
Carbon removed from the atmosphere:
- Photosynthesis (plants absorb CO₂)
Carbon moves through organisms:
- Plants fix CO₂ into glucose → eaten by animals → passed along food chains
- Dead organisms decomposed by bacteria and fungi → CO₂ released
- Some dead organisms not decomposed → form fossil fuels over millions of years
2. The Water Cycle
- Evaporation: water evaporates from oceans, lakes, rivers (energy from sun)
- Transpiration: water evaporates from plant leaves
- Condensation: water vapour cools → forms clouds
- Precipitation: rain, snow, etc. falls
- Collection: water collects in rivers, lakes, oceans, or seeps into groundwater
The water cycle is driven by energy from the sun.
3. Decomposition
Decomposers: bacteria and fungi break down dead matter.
Factors affecting rate of decomposition:
| Factor | Effect |
|---|---|
| Temperature | Warm → faster (enzyme activity) |
| Moisture | Moist → faster |
| Oxygen | Aerobic decomposition is faster |
Compost
Gardeners use decomposition: warm, moist, aerated conditions speed up composting.
4. Required Practical: Decomposition
Investigate effect of temperature on rate of decomposition:
- Use milk + lipase (to simulate breakdown)
- Add phenolphthalein indicator (pink in alkaline)
- Time how long until colour disappears (fat broken down → acidic)
- Repeat at different temperatures
5. Practice Questions
- Name two processes that release CO₂ into the atmosphere.
- Describe how carbon from CO₂ in the air can end up in an animal.
- List the four stages of the water cycle.
- Explain three factors that affect the rate of decomposition.
- Why are decomposers essential for nutrient recycling?
Want to check your answers and get step-by-step solutions?
Summary
- Carbon cycle: photosynthesis removes CO₂; respiration, combustion, decomposition return it
- Water cycle: evaporation → condensation → precipitation → collection
- Decomposers: bacteria and fungi; recycle nutrients back to soil
- Rate of decomposition: affected by temperature, moisture, oxygen