4c) Cycles within ecosystems

Paper Two- The Water Cycle:
The movement of water molecules between various locations. 



Precipitation: water from clouds to the ground
Condensation: Gas to liquid 
Transpiration: water leaves as a gas 
Evaporation: liquid to gas 
Percolation: process for a liquid slowly going through a filter e.g. soil 

The Carbon cycle:

Carbon is passed from the atmosphere as Carbon Dioxide to living organisms. It is then passed to one organism to the next in complex molecules and then finally returns to the atmosphere.



The only thing that removes CO₂ from the air is photosynthesis. Plants use it to make fats, carbohydrates and protein. Both plant and animal respiration puts CO₂ back into the atmosphere.
         Carbon from dead animals and plants can end up as fossil fuels, when this is burned (combustion) it releases carbon. Some dead animal and plants could be broken down by micro-organisms or be turned into useful products by humans.

Paper Two- The Nitrogen Cycle:

Atmosphere contains 78% nitrogen gas which is very unreactive so can't be therefore used directly by plants and animals 
Nitrogen is needed for making proteins for growth, so living organisms need to get it from somewhere 
Plants from soil--> nitrogen in the air is turned into nitrates before plants can use it 
Animals from plants--> get protein from eating plants 
Nitrogen fixation: turning nitrogen in the air to nitrogen compounds in the soil which plants can use. 
Two main ways:

• Lightning- nitrogen react with oxygen due to the energy from the lightning bolt. 
• Nitrogen fixing bacteria in roots and soil 

Different types of bacteria involved in the nitrogen cycle:

• Decomposers- break down of proteins, urea and ammonia 
• Nitrifying bacteria- ammonia into nitrates 
• Nitrogen fixing bacteria- N₂ into nitrogen compounds 
• Denitrifying bacteria- nitrates back into N₂