Nutrient Cycles Flashcards
What happens during nitrogen fixation
Nitrogen gas in the atmosphere is turned into nitrogen containing compounds
Bacteria turns nitrogen into ammonia, which goes onto to form ammonium ions in solution that can be used by plants
Nitrogen fixing bacteria is found root nodules of leguminous plants
They form a mutualistic relationship with the plants - they provide the plant with nitrogen compounds and the plant provides them with carbohydrates
What happens during ammonification
Nitrogen compounds from dead organisms are turned into ammonia by saprobionts which goes on to form ammonium ions. They break down proteins into smaller molecules by extracellular digestion
Animal waste also contains nitrogen compounds, these are also turned into ammonia by saprobionts and go to form ammonium ions
What happens during nitrification
Ammonium ions in the soil are changed into nitrates which can be used by plants :
Oxidation of ammonium ions to nitrites with help from nitrifying bacteria
Then nitrifying bacteria changes nitrite into nitrate by oxidation
What is denitrification
Nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - they use nitrates in the soil to carry out respiration and produce nitrogen gas
This happens under anaerobic conditions e.g. waterlogged soils
Denitrification reduces the availability of nitrogen containing compounds for plants, however can we make this more productive
The soils on which crops grow must be kept well aerated to prevent the build up of nitrifying bacteria
Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants
Saprobionts breakdown proteins into smaller molecules by extra cellular digestion
Ammonia is produced
This is converted into nitrite to nitrate by oxidation and nitrifying bacteria
Describe the phosphorus cycle
Phosphate ions in rocks are released into the soil by weathering
Phosphate ions are taken into the plant through the roots. Mycorrhizae greatly increases the rate at which phosphorus can be assimilated
Phosphate ions are transferred through the food chain as animals eat the plants are in turn eaten by other animals
Phosphate ions are lost from the animals in waste products
When plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation (absorbed) by plants. The microorganisms also release the phosphate ions from urine and faeces
Weathering of rocks also releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, such as algae, and passed along the food chain to birds
The waste products by sea birds is known as guano and contains a high proportion of phosphate ions. Guano returns a significant amount of phosphate ions to soils. It is often used as a natural fertiliser
What does mycorrhizae do
The fungi acts like extensions of the plants root system and vastly increase the total surface area for the absorption of water and minerals
Acts like a sponge and holds water and minerals in the neighbourhood of the roots
Improves rate of uptake
Fungus receives organic compounds such as sugars and amino acids from the plant
