5.4: Nitrogen Cycle Flashcards
Name 2 common elements recycled by microorganisms
nitrogen and phosphorus
name 2 biological molecules containing nitrogen
amino acids, nucleic acids
name 2 biological molecules containing phosphorus
phospholipid, ATP
Describe the role of saprobionts in decomposition
Saprobionts secrete digestive enzymes onto the DOM, these enzymes hydrolyse the biological molecules in the DOM. The soluble products of the hydrolysis can be absorbed back into the fungi hyphae. The inorganic/ammonium/phosphate ions remain in the soil available to plants. The saprobionts respire aerobically releasing carbon dioxide
What are the 4 processes of the Nitrogen Cycle
Nitrogen fixing, Ammonification, Nitrification, Denitrification
What are legumes
Nitrogen fixing plants
What type of bacteria carries out the process of nitrogen fixing
Nitrogen fixing bacteria
What nitrogen conversion occurs during the process of nitrogen fixing
Reduction
N2 -> NH3
What type of respiration do the bacteria do during the process of nitrogen fixing
aerobic
What type of bacteria carries out the process of ammonification
Saprobionts
What nitrogen conversion occurs during the process of ammonification
Amino Acids -> NH3
What type of respiration do the bacteria do during the process of ammonification
aerobic
What type of bacteria carries out the process of Nitrification
Nitrifying bacteria
What nitrogen conversion occurs during the process of nitrification
oxidation
NH3 -> NO2- -> NO3-
What type of respiration do the bacteria do during the process of nitrification
aerobic
What type of bacteria carries out the process of denitrification
denitrifying bacteria
What nitrogen conversion occurs during the process of denitrification
reduction
NO3- -> N2
What type of respiration do the bacteria do during the process of denitrification
anaerobic
Nitrogen fixing bacteria do what do nitrogen?
reduce N2 to NH3 (ammonia)
Saprobionts do what do amino acids?
convert it to ammonia
nitrifying bacteria do what to ammonia?
oxidise ammonia to nitrite ions, and further oxidise that to nitrate ions
denitrifying bacteria do what to nitrate ions?
reduce it to nitrogen
How do legumes gain an advantage in N-poor soils
they outcompete other plants
How are legumes at a disadvantage in N-rich soils
any other plant outcompetes legumes
Explain how legumes carry out their process of nitrogen fixing
Rhizobium bacteria on the plant roots produce nodules which fix nitrogen in the atmosphere and convert it into ammonia
Why do plants need nitrogen
for the synthesis of amino acids
why is nitrogen in the atmosphere not directly available to plants
it has a triple bond making it a very stable molecule
how could you identify plants growing in N-poor soils
stunted growth
how does deforestation affect the nitrogen cycle
increase in soil erosion, increase in leaching of nitrates out of soil and so decrease in quality of soil
how does crop rotation improve soil fertility
increases it as nitrogen stays in the soil
how does an increase in animal waste affect the nitrogen cycle
increase in DOM, increase in ammonification, increase in nitrates in soil
what would happen if a farmer used too much fertiliser (N cycle)
excess nitrates leached out of soil into surrounding water bodies causing eutrophication
Explain the symbiotic relationship between legumes and nitrogen fixing bacteria
legumes get N compounds
bacteria get C compounds
How does harvesting of crops affect N cycle
decrease in N2 in soil
Why is it necessary for farmers to plough their fields (N cycle)
to aerate the soil which decreases denitrification and increases nitrification
Fully explain the nitrogen cycle
Atmospheric N2 -> nitrogen fixing bacteria convert N2 to NH3 -> proteins in plants -> DECOMPOSITION/ feeding -> proteins in animals -> DECOMPOSITION/excretion -> PROTEINS IN DOM/nitrogenous waste(urea) -> ammonification by saprobionts -> NH3 in soil -> nitrification -> NO2- in soil -> further nitrification -> NO3- in soil
-> denitrification into atmospheric N2/absorption by plants
Describe how an atom of nitrogen in a soil nitrate ion could become part of a protein molecule in a plant
nitrates absorbed into plant roots via active transport, these nitrates are used to synthesise amino acids, which are then used in translation of mRNA to a polypeptide chain to form proteins
