The Nitrogen Cycle Flashcards
In natural ecosystems, how are nitrate levels restored?
The recycling of nitrogen-containing compounds
How are nitrate ions taken up by plants?
They are absorbed by active transport in the root hairs
How are nitrate levels restored in agricultural ecosystems?
Through the addition of fertilisers
What are the 4 main stages in the nitrogen cycle?
Ammonification, nitrification, nitrogen fixation and denitrification
What is ammonification?
The production of ammonia from organic ammonium-containing compounds
Which type of microorganisms release ammonia from organic ammonium-containing compounds?
Saprobiotic microorganisms such as fungi and bacteria
What occurs during nitrification?
Ammonium ions are converted to nitrate ions through an oxidation reaction carried out by nitrifying bacteria. Oxidation reactions first convert ammonium ions to nitrite ions and then nitrite ions are oxidised to nitrate ions.
What do nitrifying bacteria require to carry out their conversions?
Oxygen
How can the productivity of nitrifying bacteria be increased?
Farmers must keep soil structure light and well aerated by ploughing and ensuring good drainage
What happens during nitrogen fixation?
Nitrogen gas is converted into nitrogen-containing compounds
What are the two types of microorganisms that carry out nitrogen fixation?
Free-living nitrogen fixing bacteria and mutualistic nitrogen-fixing bacteria
What are mutualistic nitrogen-fixing bacteria?
These bacteria live in the root nodules of leguminous plants and obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria
When does denitrification occur?
When soils become waterlogged, and there is a shortage of oxygen. Anaerobic conditions
What occurs during denitrification?
Soil nitrates are converted into gaseous nitrogen
