nitrogen cycle

give 5 examples of nitrogen containing molecules:

• amino acids

• DNA

• RNA

• ATP

• ADP

what is the significance of the N₂ cycle?

shows how different microorganisms are needed to convert N₂ gas into nitrogen-containing compounds that can be absorbed by plants and animals

give 3 conditions required for decomposition:

• warm temperature

• moisture

• oxygen

what is a detritivore? give 4 examples:

• organism that ingests/digests dead/decaying organic matter internally

• e.g. worms, millipedes, woodlice, slugs

what is a saprobiont? give an example:

• microorganism which secretes enzymes to decompose N containing compounds externally and absorbs simpler molecules

• e.g. microbes, primarily bacteria and fungi

give the stages of the nitrogen cycle:

1. nitrogen fixation

2. ammonification

3. nitrification

4. denitrification

describe the process of nitrogen fixation:

• free living nitrogen-fixing bacteria for N₂ → NH₃/NH₄⁺

• mutualistic nitrogen fixing bacteria (e.g. Rhizobium) in root nodules of leguminous plants fix N₂ into NH₃ which is converted into amino acids

• in turn, the plant provides the bacteria w/ carbohydrates

• abiotic processes - lighting, artificial fertilisers, Haber process - can also fix N₂

what is nitrogen-fixation?

the conversion of atmospheric nitrogen gas into nitrogen containing compounds like ammonia

describe the process of ammonification:

• death/excretion of living organisms releases nitrogen-rich containing substances e.g. urea, proteins, nucleic acids, vitamins

• saprobionts decompose these into ammonium ions (NH₄⁺)

• NH₄⁺ can now be absorbed (AT through root hair cells) and assimilated by plants

what is ammonification?

conversion of organic N₂ containing compounds in dead organisms or waste into NH₃ or NH₄⁺ ions by saprobionts

describe the process of nitrification:

• nitrifying bacteria oxidise NH₄⁺ ions to nitrite ions - NO₂^-

• these are then oxidised again into nitrate ions - NO₃^-

• (most nitrogen taken up by plants is in the form of nitrate ions)

what is nitrification?

NH₃ and NH₄⁺ are oxidised to NO₂^- then NO₃^- which plants can absorb via AT and assimilate

what is denitrification?

the conversion of NO₃^- ions back into N₂ gas by anaerobic denitrifying bacteria

what conditions might allow denitrification to take place?

anaerobic conditions

how might excessive denitrification -vely impact plant growth? what farming techniques can prevent this?

• excessive denitrification may lead to stunted growth as prevents the plant from making proteins

• to prevent this: frequently aerate the soil, keeping conditions aerobic