5.4: Nitrogen Cycle

Question 1

Name 2 common elements recycled by microorganisms

Answer 1

nitrogen and phosphorus

Question 2

name 2 biological molecules containing nitrogen

Answer 2

amino acids, nucleic acids

Question 3

name 2 biological molecules containing phosphorus

Answer 3

phospholipid, ATP

Question 4

Describe the role of saprobionts in decomposition

Answer 4

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

Question 5

What are the 4 processes of the Nitrogen Cycle

Answer 5

Nitrogen fixing, Ammonification, Nitrification, Denitrification

Question 6

What are legumes

Answer 6

Nitrogen fixing plants

Question 7

What type of bacteria carries out the process of nitrogen fixing

Answer 7

Nitrogen fixing bacteria

Question 8

What nitrogen conversion occurs during the process of nitrogen fixing

Answer 8

Reduction
N2 -> NH3

Question 9

What type of respiration do the bacteria do during the process of nitrogen fixing

Answer 9

aerobic

Question 10

What type of bacteria carries out the process of ammonification

Answer 10

Saprobionts

Question 11

What nitrogen conversion occurs during the process of ammonification

Answer 11

Amino Acids -> NH3

Question 12

What type of respiration do the bacteria do during the process of ammonification

Answer 12

aerobic

Question 13

What type of bacteria carries out the process of Nitrification

Answer 13

Nitrifying bacteria

Question 14

What nitrogen conversion occurs during the process of nitrification

Answer 14

oxidation
NH3 -> NO2- -> NO3-

Question 15

What type of respiration do the bacteria do during the process of nitrification

Answer 15

aerobic

Question 16

What type of bacteria carries out the process of denitrification

Answer 16

denitrifying bacteria

Question 17

What nitrogen conversion occurs during the process of denitrification

Answer 17

reduction
NO3- -> N2

Question 18

What type of respiration do the bacteria do during the process of denitrification

Answer 18

anaerobic

Question 19

Nitrogen fixing bacteria do what do nitrogen?

Answer 19

reduce N2 to NH3 (ammonia)

Question 20

Saprobionts do what do amino acids?

Answer 20

convert it to ammonia

Question 21

nitrifying bacteria do what to ammonia?

Answer 21

oxidise ammonia to nitrite ions, and further oxidise that to nitrate ions

Question 22

denitrifying bacteria do what to nitrate ions?

Answer 22

reduce it to nitrogen

Question 23

How do legumes gain an advantage in N-poor soils

Answer 23

they outcompete other plants

Question 24

How are legumes at a disadvantage in N-rich soils

Answer 24

any other plant outcompetes legumes

Question 25

Explain how legumes carry out their process of nitrogen fixing

Answer 25

Rhizobium bacteria on the plant roots produce nodules which fix nitrogen in the atmosphere and convert it into ammonia

Question 26

Why do plants need nitrogen

Answer 26

for the synthesis of amino acids

Question 27

why is nitrogen in the atmosphere not directly available to plants

Answer 27

it has a triple bond making it a very stable molecule

Question 28

how could you identify plants growing in N-poor soils

Answer 28

stunted growth

Question 29

how does deforestation affect the nitrogen cycle

Answer 29

increase in soil erosion, increase in leaching of nitrates out of soil and so decrease in quality of soil

Question 30

how does crop rotation improve soil fertility

Answer 30

increases it as nitrogen stays in the soil

Question 31

how does an increase in animal waste affect the nitrogen cycle

Answer 31

increase in DOM, increase in ammonification, increase in nitrates in soil

Question 32

what would happen if a farmer used too much fertiliser (N cycle)

Answer 32

excess nitrates leached out of soil into surrounding water bodies causing eutrophication

Question 33

Explain the symbiotic relationship between legumes and nitrogen fixing bacteria

Answer 33

legumes get N compounds bacteria get C compounds

Question 34

How does harvesting of crops affect N cycle

Answer 34

decrease in N2 in soil

Question 35

Why is it necessary for farmers to plough their fields (N cycle)

Answer 35

to aerate the soil which decreases denitrification and increases nitrification

Question 36

Fully explain the nitrogen cycle

Answer 36

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

Question 37

Describe how an atom of nitrogen in a soil nitrate ion could become part of a protein molecule in a plant

Answer 37

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