Cycling materials (AQA GCSE Biology Combined Science): Revision Notes
Cycling materials
Living things need materials like carbon and water to survive. These materials don't disappear - they get recycled through ecosystems again and again. This recycling keeps life going on Earth.
The cycling of materials is one of the most important processes in nature. Without these cycles, life on Earth would quickly run out of essential resources like water and carbon compounds.
The water cycle
The water cycle moves water around the planet. It provides fresh water for all living things.
How water moves around
Water constantly moves between the oceans, the air, and the land. Here's how it works:
Evaporation - Heat from the sun turns water from oceans, rivers and lakes into water vapour. This rises into the atmosphere.
Transpiration - Plants also release water vapour through their leaves. This happens when plants lose water during photosynthesis.
Condensation - When water vapour cools down high in the atmosphere, it turns back into tiny water droplets. These form clouds.
Precipitation - Water falls back to Earth as rain or snow. Some of this water soaks into the ground, and some flows back to the oceans through rivers.
Worked Example: Following a Water Molecule
Imagine following a single water molecule through the complete cycle:
- Ocean: The molecule starts in the ocean
- Evaporation: Solar energy causes it to evaporate and rise as water vapour
- Condensation: It cools in the atmosphere and condenses into a cloud droplet
- Precipitation: It falls as rain onto land
- Collection: It flows through a river back to the ocean
- Cycle repeats: The same molecule can now evaporate again
The cycle then starts all over again. This means the same water gets used many times by different living things.
The carbon cycle
Carbon is found in all living things. The carbon cycle moves carbon between the atmosphere, living things, and the ground.
How carbon moves through ecosystems
Carbon moves around in several important ways:
Photosynthesis - Plants absorb carbon dioxide gas from the air. They use it to make sugars and other carbon compounds during photosynthesis.
Feeding - When animals eat plants, the carbon compounds pass into the animals. When animals eat other animals, carbon moves along the food chain.
Respiration - All living things (plants and animals) release carbon dioxide back into the air when they respire. This happens when they break down food for energy.
Decomposition - When plants and animals die, decomposers like bacteria and fungi break them down. This releases carbon dioxide back into the atmosphere.
Combustion - Burning fossil fuels (like coal and oil) releases carbon that was stored underground for millions of years. This adds extra carbon dioxide to the atmosphere.
Human Impact on the Carbon Cycle
Burning fossil fuels adds extra carbon dioxide to the atmosphere that wouldn't naturally be there. This disrupts the natural balance of the carbon cycle and is a major cause of climate change.
The role of decomposers
Decomposers are really important for recycling materials. These tiny organisms include bacteria and fungi.
Decomposers feed on dead plants and animals. They break down this dead material and use the nutrients to grow. As they do this, they release carbon dioxide into the atmosphere.
The decomposition process is like nature's recycling system. Without decomposers, dead organic matter would pile up everywhere and essential nutrients would never be returned to the ecosystem.
Sometimes worms, beetles and other small creatures start the breakdown process by eating dead organisms first. Then the decomposers finish the job.
Decomposers also return other important nutrients to the soil. For example, they release nitrate ions that plants need to make proteins.
Key processes summary
Key Points to Remember:
In the water cycle:
- Evaporation and transpiration move water into the atmosphere
- Precipitation brings water back to Earth
In the carbon cycle:
- Photosynthesis removes carbon dioxide from the air
- Respiration, decomposition and combustion add carbon dioxide to the air
Both cycles are essential because they make sure materials get reused rather than running out.
Remember!
Essential Facts:
- Water and carbon constantly cycle through ecosystems - nothing gets wasted
- The water cycle provides fresh water through evaporation, condensation and precipitation
- Plants remove carbon dioxide during photosynthesis, but respiration puts it back
- Decomposers break down dead material and recycle nutrients back to the soil
- Burning fossil fuels adds extra carbon dioxide to the atmosphere