nitrogen cycle

Question 1

what is nitrogen required for?

Answer 1

to make proteins

Question 2

why can’t plants or animals absorb nitrogen from the air?

Answer 2

N2 gas is very stable and the bonds holding the nitrogen atoms together would need massive amounts of energy to break

Question 3

what are the 2 nitrogen atoms held together by?

Answer 3

a triple covalent bond

Question 4

what are the 2 ways nitrogen can be taken out of the air?

Answer 4

nitrogen fixing bacteria
lightning

Question 5

where is nitrogen fixing bacteria found?

Answer 5

“free living” in soil and in the root nodules of leguminous plants (peas, beans, clover)

Question 6

what does nitrogen fixing bacteria do?

Answer 6

take N2 gas and change it into nitrates in the soil

Question 7

what does lightning do to N2 gas?

Answer 7

splits the bond between the two atoms and turns them into nitrous oxides like N20 and NO2 that dissolve in rainwater and “leach” into the soil

Question 8

what do plants do with the nitrates they find in the soil?

Answer 8

they absorb them

Question 9

what do plants use the nitrates they absorb to do?

Answer 9

they make proteins

Question 10

how do animals get nitrogen?

Answer 10

they eat the plants (or other animals) and get the nitrogen they need from the proteins in the plant or animals

Question 11

what does waste from animals do?

Answer 11

sends nitrogen back into the soil as ammonium compounds (the urea in urine contains nitrogen)

Question 12

what happens when animals and plants die?

Answer 12

they decay and all the proteins inside them are broken down into ammonium compounds and put back into the soil by decomposers

Question 13

what does nitrifying bacteria do?

Answer 13

converts the ammonium compounds into nitrites and then to nitrates, which can then be absorbed by plants

Question 14

what is nitrification?

Answer 14

the conversion of ammonium compounds to nitrites and then to nitrates

Question 15

what is assimilation?

Answer 15

animals eat plants- they digest the proteins and DNA, absorbing the small soluble molecules (amino acids and nucleotides)- these are used by the animal to synthesise new proteins and DNA

Question 16

where is denitrifying bacteria found?

Answer 16

in poorly aerated soil (not much oxygen)

Question 17

what does denitrifying bacteria do?

Answer 17

take the nitrates out of the soil and convert them back into N2 gas

Question 18

what is denitrification?

Answer 18

nitrates are converted to nitrogen gas
denitrification reduces the amount of nitrate in the soil and therefore makes the soil less fertile

Question 19

how can farmers reduce the amount of denitrifying bacteria?

Answer 19

ploughing and turning over the soil

Question 20

what is decomposition?

Answer 20

protein in dead plants and animals is broken down
ammonia is released into the soil

Question 21

what bacteria is involved in decomposition?

Answer 21

decomposing bacteria

Question 22

what is nitrification?

Answer 22

ammonia is converted to nitrites and nitrites are converted into nitrates

Question 23

what bacteria does nitrification involve?

Answer 23

nitrifying bacteria

Question 24

what is nitrogen fixation?

Answer 24

nitrogen gas is converted to ammonia in bacteria which is used to make proteins, when the bacteria die their proteins decompose, releasing ammonia back into the soil

Question 25

what bacteria is involved in nitrogen fixation?

Answer 25

nitrogen-fixing bacteria found in soil and in root nodules of plants

Question 26

how is the nitrogen fixing bacteria (nodules) on the root of legume plants mutualistic?

Answer 26

the bacteria receive glucose from the plant, while the plant absorbs ammonia from the bacteria in the nodule

Question 27

what happens when nitrogen fixing bacteria decompose?

Answer 27

they make the soil much more fertile- releasing ammonia which can be converted into nitrates

Question 28

why might farmers rotate the crops they grow in each field?

Answer 28

they grow leguminous plants- these bacteria decompose and make the soil more fertile