Flashcards
The nitrogen cycle
Flashcards do conjunto (11)
- 1The Nitrogen CycleAll living organisms require nitrogen to manufacture proteins, nucleic acids and other nitrogen-containing compounds
- 278% of the atmosphere is nitrogenplants take in nitrogen in the form of nitrate ions ( NO3-) from the soil
- 3The nitrate ions are absorbed by active transport by the root hairs ( Nitrogen enters the living component of the system)Animals obtain nitrogen-containing compounds by eating and digesting plants
- 4Nitrate ions are soluble and easily leach through the soil, beyond the reach of plant rootsIn natural ecosystems, the soil nitrate levels are restored through the recycling of nitrogen-containing compounds
- 5In agricultural ecosystems, levels are further increased by the addition of fertilisersWhen plants and animals die, decomposition begins in which micro-organisms replenish nitrate levels in the soil. Little nitrate available from other sources
- 6Ammonification - production of ammonia from organic ammonium containing compounds e.g. urea, proteins, nucleic acids and vitamins found in faeces and dead organismsSaprobiotic micro-organisms feed on these materials releasing ammonia which then forms ammonium ions in the soil. This is where nitrogen returns to the non-living component of the eco-system.
- 7Nitrification - conversion of ammonium ions to nitrate ions. This is an oxidation reaction and so releases energy - carried out by free-living soil micro-organisms called nitrifying bacteria.Occurs in 2 stages:
1. oxidation of ammonium ions to nitrite ions (NO-2)
2. oxidation of nitrite ions to nitrate ions (NO-3) - 8Nitrifying bacteria require oxygen to carry out these conversions, so they need soil with many air spaces.Good drainage prevents air spaces being filled with water and prevents air being forced out of soil.
- 9Nitrogen fixation - Nitrogen gas converted into nitrogen-containing compoundscarried out industrially and when lightning passes through the atmosphere
- 10carried out by: free-living nitrogen-fixing bacteria which reduce gaseous nitrogen to ammonia, which is then used to manufacture amino acids. Nitrogen rich compounds are released when they die and decay.Mutualistic nitrogen-fixing bacteria: bacteria live in nodules on roots of plants such as peas and beans. They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.
- 11Denitrification - Soil becomes waterlogged, therefore shortage of oxygen, type of micro-organism changes. Fewer aerobic nitrifying and nitrogen-fixing bacteria present and there is an increase in anaerobic denitrifying bacteria.Anaerobic denitrifying bacteria convert soil nitrates into gaseous nitrogen. This reduces the availability of nitrogen-containing compounds for plants.
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- FlashCards sobre The nitrogen cycle, criado por alice.d18 em 16-05-2015.
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