The nitrogen cycle Flashcards
Why is nitrogen required by organisms ?
Plants and animals require nitrogen in order to produce proteins and nucleic acids (DNA and RNA)
Why do plants and animals need the nitrogen cycle ?
plants and animals cannot access the nitrogen gas in the atmosphere.
Instead, they rely on certain bacteria to convert the nitrogen gas into nitrogen-containing compounds, which can be taken up by plants
What happens during Nitrogen fixation ?
Atmospheric nitrogen gas is converted into nitrogen-containing compounds. The nitrogen fixing bacteria (such as Rhizobium) convert nitrogen into ammonia, which forms ammonium ions (in solution) that can then be used by plants.
Where are Nitrogen fixing bacteria found ?
These nitrogen-fixing bacteria are found inside the root nodules (small growths on the roots) of leguminous plants such as peas, beans and clover
What is the relationship like between the nitrogen fixing bacteria and the leguminous plants ?
The bacteria have a symbiotic (mutually beneficial) relationship with these plants - the bacteria provide the plants with nitrogen-containing compounds and the plants provide the bacteria with organic compounds such as carbohydrates.
What happens during Ammonification ?
Nitrogen compounds in waste products (e.g. urine and faeces) and dead organisms are converted into ammonia by saprobionts (a type of decomposer including some fungi and bacteria)
This ammonia forms ammonium ions in the soil.
What happens during nitrification ?
The ammonium ions in the soil are converted by nitrifying bacteria into nitrates.
Initially, nitrifying bacteria such as Nitrosomonas convert ammonium ions into nitrites
Different nitrifying bacteria then convert these nitrites into nitrates.
What happens during Denitrification ?
Denitrifying bacteria use nitrates in the soil during respiration
This process produces nitrogen gas, which returns to the atmosphere.
This process occurs in anaerobic conditions (when there is little or no oxygen available, such as in waterlogged soil)
Denitrification is when nitrates in the soil are converted to nitrogen gas by denitrifying bacteria.
Why is the nitrogen cycle important ?
All living organisms require a source of nitrogen to manufacture proteins, nucleic and other nitrogen containing compounds such as chlorophyll
Crops cannot grow to their full potential without an adequate supply of nitrogen
What farming practices add nitrogen compounds to a field ?
growing legumes
Spread manure, slurry - decomposed to release nitrates
Add cattle to graze- Add dung, urine
What farming practices remove nitrogen from a field ?
uptake of nitrates/ammonium compounds by crop
farm animals eat plants
then animals removed before they decompose
Bare soil removal
Leaching of nitrates and soil erosion.
What are saprobionts ?
Decomposers that carry out Extracellular digestion
What is the role of Saprobionts ?
to obtain nutrients from dead or waste organic matter
to release the nutrients back into the environment to be absorbed by other organisms (e.g. plants)
What type of digestion do saprobionts carry out ?
Extra-cellular digestion
Explain the Extra-cellular digestion of saprobionts
Saprobionts secrete enzymes onto their food (dead organisms and waste material), which then digest the material externally
The products of this external digestion are then absorbed by the saprobionts
