The Nitrogen Cycle Flashcards
Why do living organisms need a source of nitrogen?
Nitrogen is needed to make essential nitrogen containing compounds, such as amino acids, proteins , nucleic acids and ATP
In what form does nitrogen have to be in, so that plants can make use of it?
Nitrate ions
How do nitrates enter producer and consumer pathways?
Nitrates are absorbed by root hair cells via active transport, then used to make organic compounds like proteins.
The plant proteins are then ingested by animals, subsequently digested and then built up again into animal proteins
What happens to the nitrogen containing compounds in plants and animal eventually?
They are excreted as urea, egested in faeces or end up in non-living organic matter following death
In order to recycle the nitrogen in excreted materials, faeces and dead organisms, what processes and organisms are involved?
Decay and decomposition by bacteria and fungi (saprobiotic microorganisms)
They convert the nitrogen into its usable nitrate form (in a process known as mineralisation)
Decay and decomposition involves 2 main stages, what are they?
- Ammonification
- Nitrification
What does ammonification involve?
Decomposers (bacteria and fungi) break down nitrogen rich compounds (proteins in the dead organisms, faeces and urea) into ammonium ions in the soil
How do detritivores such as earthworms, help with decay/ammonification?
Detritivores break down the dead organisms into smaller pieces, which have a bigger surface area, thereby helping the bacteria and fungi carry out the process of decomposition throughout the soil
What happens during nitrification?
The ammonium ions are now converted to nitrate by nitrifying bacteria (such as nitrosomas and nitrobacter)
The profess of nitrification is actually split into 2 stages. What are they?
- Ammonium ions are converted to nitrite ions
- Nitrite ions are converted to nitrate ions
Why do the nitrifying bacteria require a good supply of oxygen?
The process of nitrification is aerobic as the reactions involved are oxidation reactions
How do nitrate ions get into plants?
The nitrate ions are absorbed by root hair cells from the soil, by the process of active transport. This process requires energy from respiration, so a supply of oxygen is needed.
What happens during the process of nitrogen fixation?
During nitrogen fixation, nitrogen-fixing bacteria (eg Rhizobium) convert nitrogen gas from the air into nitrogen containing compounds such as ammonium
Where are nitrogen fixing bacteria found?
-free living in the soil
-in root nodules of plants called legumes
The relationship between the legumes and the nitrogen fixing bacteria is mutualistic, explain
The bacteria have a stable environment with a supply of carbohydrate from the plant, the plant gains nitrogen compounds from the bacteria
How does the process of nitrogen fixation and growing legumes benefit a farmer?
By growing legumes (as part as crop rotation) and then allowing them to decay in the soil, the soil is enriched by nitrogen compounds (ammonium and nitrate) which are then used for growth by the crops subsequently grown there
What other processes can lead to nitrogen fixation of atmospheric nitrogen?
Lightning
Apart from being useful to the farmer, how else is nitrogen fixation important?
Ecologically, nitrogen fixers at colonisers of barren land, as they can survive in nitrogen deficient soils
What is denitrification?
During denitrification, denitrifying bacteria (like pseudomonas) convert nitrates in the soil back into atmospheric nitrogen
What negative impact do denitrifying bacteria cause?
They significantly lower soil fertility for growing crops
What sort of conditions do denitrifying bacteria thrive in?
Anaerobic conditions- found typically in waterlogged or very compacted soil
What benefits do earthworms bring to soil?
Their burrowing aerates the soil, making it more suitable for nitrification and nitrogen fixation and less suitable for denitrifying bacteria
