the nitrogen cycle Flashcards
what is the nitrogen cycle?
flow of organic and inorganic nitrogen within the abiotic and biotic components of an ecosystem, where there is an interchange between nitrogenous compounds and atmospheric nitrogen
why is nitrogen important to all living organisms?
amino acids for protein synthesis
chlorophyll
nitrogenous bases in nucleotides
due to plants and animals not be able to us atmospheric nitrogen, how can nitrogen enter the food chain?
plants absorb ammonium or nitrate ions through their roots
nitrogenous compounds pass to consumers when consuming plants
by which processes do these ions get taken up by plant roots?
active transport
facilitated diffusion
name two pathways that these ions can take when travelling through the cortex cells of a plant root
symplast –> water and ions move through cytoplasm and plasmodesmata
apoplast –> water and ions move through the cell walls
what are the five main processes in the nitrogen cycle?
ammonification
nitrification
nitrogen fixation
assimilation
denitrification
what happens in the ammonification stage?
decomposers –> saprotrophs and detritivores
results in decay of dead plants and animals
faeces and urine into ammonium ions
what happens in nitrification stage?
ammonium ions produced by decomposers –> nitrates
nitrates (nitrifying bacteria) –> nitrites
what conditions are needed in nitrification?
aerobic conditions
when the nitrates are converted to nitrites in nitrification, what happens to the ions?
absorbed by plants
incorporated into amino acids, nucleotides and chlorophyll
what are the two types of nitrifying bacteria?
nitrosomonas
nitrobacter
nitrosomonas
covert ammonium ions –> nitrites
nitrobacter
convert nitrites –> nitrates
what happens in the nitrogen fixing stage?
nitrogen fixing bacteria directly fixes nitrogen gas into ammonium ions
what are the two types of nitrogen fixing bacteria?
azotobacter
rhizobium
azotobacter
free living in soil
rhizobium
found in root nodules of leguminous plants
what type of bacteria is rhizobium?
symbiotic bacteria
what are some examples of root nodules of legumes?
clover
pea plants
what happens nitrogen gas diffuses into the root nodule?
rhizobium produces nitrogenase enzyme
what is the purpose of the nitrogenase enzyme?
catalyses the fixation of nitrogen gas into ammonium ions
what are the ammonia ions converted to after the nitrogenase enzyme catalyses the fixation of nitrogen gas into ammonium ions?
amino acids for use by the plant
what is the nitrogenase enzyme inhibited by and what does this lead to?
oxygen
haemoglobin is present in root nodules to bind with the oxygen
presence of haemoglobin gives them a pink colour
why can the relationship between the bacteria in the root nodule and the legume be classed as a symbiotic relationship?
bacteria gain sugars from plant photosynthesis
plant gains nitrogenous compounds
what happens in the assimilation stage?
formation of organic nitrogen compounds from inorganic nitrogen compounds present in the environment
what happens in the denitrification stage?
denitrifying bacteria convert nitrate (soil) –> nitrogen gas
why is the denitrification stage a problem?
removes useful nitrogenous compounds from the soil
what is an example of a denitrifying bacteria?
pseudomonas
what conditions are needed for denitrification to occur?
anaerobic conditions
where does denitrification most occur often?
waterlogged soils
how can ploughing and drainage of soil aid the nitrogen cycle?
improves aeration
enables nitrifying bacteria to convert ammonium ions –> nitrate
prevents denitrifying bacteria from completing denitrification
how can the cultivation of legumes in soil that lack nitrogen aid the nitrogen cycle?
rhizobium will carry out nitrogen fixation within the plants
when plants die, nitrogenous compounds will enter the soil
broken down by decomposers in ammonification
how can the application of artificial fertilisers and manure to soil aid with the nitrogen cycle?
enable a greater yield of crop plants
