the nitrogen cycle

Question 1

what is the nitrogen cycle?

Answer 1

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

Question 2

why is nitrogen important to all living organisms?

Answer 2

amino acids for protein synthesis
chlorophyll
nitrogenous bases in nucleotides

Question 3

due to plants and animals not be able to us atmospheric nitrogen, how can nitrogen enter the food chain?

Answer 3

plants absorb ammonium or nitrate ions through their roots

nitrogenous compounds pass to consumers when consuming plants

Question 4

by which processes do these ions get taken up by plant roots?

Answer 4

active transport
facilitated diffusion

Question 5

name two pathways that these ions can take when travelling through the cortex cells of a plant root

Answer 5

symplast –> water and ions move through cytoplasm and plasmodesmata

apoplast –> water and ions move through the cell walls

Question 6

what are the five main processes in the nitrogen cycle?

Answer 6

ammonification
nitrification
nitrogen fixation
assimilation
denitrification

Question 7

what happens in the ammonification stage?

Answer 7

decomposers –> saprotrophs and detritivores

results in decay of dead plants and animals

faeces and urine into ammonium ions

Question 8

what happens in nitrification stage?

Answer 8

ammonium ions produced by decomposers –> nitrates

nitrates (nitrifying bacteria) –> nitrites

Question 9

what conditions are needed in nitrification?

Answer 9

aerobic conditions

Question 10

when the nitrates are converted to nitrites in nitrification, what happens to the ions?

Answer 10

absorbed by plants

incorporated into amino acids, nucleotides and chlorophyll

Question 11

what are the two types of nitrifying bacteria?

Answer 11

nitrosomonas
nitrobacter

Question 12

nitrosomonas

Answer 12

covert ammonium ions –> nitrites

Question 13

nitrobacter

Answer 13

convert nitrites –> nitrates

Question 14

what happens in the nitrogen fixing stage?

Answer 14

nitrogen fixing bacteria directly fixes nitrogen gas into ammonium ions

Question 15

what are the two types of nitrogen fixing bacteria?

Answer 15

azotobacter
rhizobium

Question 16

azotobacter

Answer 16

free living in soil

Question 17

rhizobium

Answer 17

found in root nodules of leguminous plants

Question 18

what type of bacteria is rhizobium?

Answer 18

symbiotic bacteria

Question 19

what are some examples of root nodules of legumes?

Answer 19

clover
pea plants

Question 20

what happens nitrogen gas diffuses into the root nodule?

Answer 20

rhizobium produces nitrogenase enzyme

Question 21

what is the purpose of the nitrogenase enzyme?

Answer 21

catalyses the fixation of nitrogen gas into ammonium ions

Question 22

what are the ammonia ions converted to after the nitrogenase enzyme catalyses the fixation of nitrogen gas into ammonium ions?

Answer 22

amino acids for use by the plant

Question 23

what is the nitrogenase enzyme inhibited by and what does this lead to?

Answer 23

oxygen

haemoglobin is present in root nodules to bind with the oxygen

presence of haemoglobin gives them a pink colour

Question 24

why can the relationship between the bacteria in the root nodule and the legume be classed as a symbiotic relationship?

Answer 24

bacteria gain sugars from plant photosynthesis

plant gains nitrogenous compounds

Question 25

what happens in the assimilation stage?

Answer 25

formation of organic nitrogen compounds from inorganic nitrogen compounds present in the environment

Question 26

what happens in the denitrification stage?

Answer 26

denitrifying bacteria convert nitrate (soil) –> nitrogen gas

Question 27

why is the denitrification stage a problem?

Answer 27

removes useful nitrogenous compounds from the soil

Question 28

what is an example of a denitrifying bacteria?

Answer 28

pseudomonas

Question 29

what conditions are needed for denitrification to occur?

Answer 29

anaerobic conditions

Question 30

where does denitrification most occur often?

Answer 30

waterlogged soils

Question 31

how can ploughing and drainage of soil aid the nitrogen cycle?

Answer 31

improves aeration

enables nitrifying bacteria to convert ammonium ions –> nitrate

prevents denitrifying bacteria from completing denitrification

Question 32

how can the cultivation of legumes in soil that lack nitrogen aid the nitrogen cycle?

Answer 32

rhizobium will carry out nitrogen fixation within the plants

when plants die, nitrogenous compounds will enter the soil

broken down by decomposers in ammonification

Question 33

how can the application of artificial fertilisers and manure to soil aid with the nitrogen cycle?

Answer 33

enable a greater yield of crop plants