The Nitrogen Cycle

Question 1

what percentage of the atmosphere is nitrogen gas

Answer 1

78%

Question 2

why cant nitrogen be directly used by animals and plants

Answer 2

• because nitrogen gas exists in the form N2

- and in this molecular compound form it is very unreactive

Question 3

what is nitrogen needed for by organisms

Answer 3

making proteins for growth

Question 4

what has to be done to the nitrogen gas in the air in order for plants to be able to use it

Answer 4

it needs to be turned into mineral ions such as nitrates

Question 5

how do plants obtain nitrogen

Answer 5

• they absorb the mineral ions from the soil with their roots
• and use the nitrogen in the mineral ions to make proteins

Question 6

how is nitrogen passed along the food chain

Answer 6

• it is passed in the form of proteins

- as animals eat each other

Question 7

what are the types of decomposers and what do they do

Answer 7

• bacteria and fungi in the soil
• they break down proteins in rotting animals and plants
• and urea in animal waste

Question 8

what is the result of the actions of decomposers

Answer 8

• they return nitrogen to the soil

- so the nitrogen in the organisms s recycled

Question 9

what is nitrogen fixation

Answer 9

• the process of turning nitrogen gas (N2) from the air into nitrogen-containing ions in the soil
• which plants can use

Question 10

what are the two main ways that nitrogen fixation occurs

Answer 10

• lightning

- nitrogen fixing bacteria in roots and soil

Question 11

how does lightning contribute to nitrogen fixation

Answer 11

theres so much energy in a bolt of lightning that it is enough to make nitrogen react with oxygen in the air to give nitrates

Question 12

what are the four different types of bacteria involved in the nitrogen cycle

Answer 12

• decomposers
• nitrifying bacteria
• nitrogen-fixing bacteria
• denitrifying bacteria

Question 13

what do nitrogen fixing bacteria bacteria do

Answer 13

• they turn atmospheric N2 into ammonia

- which forms ammonium nitrates

Question 14

what do nitrifying bacteria do

Answer 14

• they turn ammonia in decaying matter int nitrites

- and then into nitrates

Question 15

what do denitrifying bacteria do and where can you find them

Answer 15

• they turn nitrates back into nitrogen gas (N2)
• this is of no benefit to living organisms
• they are often found in waterlogged soils

Question 16

other than the soil, where can nitrogen fixing bacteria live in

Answer 16

• nodules on the roots of legume plants

Question 17

what do nitrogen fixing bacteria do on the nodules of roots of legume plants

Answer 17

• when the plants decompose
• the nitrogen stored in them and in their nodules is returned to the soil
• nitrogen ions can also leak out of the nodules during plant growth

Question 18

what kind of relationship do plants and nitrogen fixing bacteria have

Answer 18

• a mutualistic relationship
• the bacteria get food (sugars) from the plant
• while the plant gets nitrogen ions from the bacteria to make into proteins

Question 19

why does the nitrogen content of the soil decrease when crops are farmed and what can it lead to

Answer 19

• crops take up nitrates from the soil as they grow
• but when they are harvested, rather than dying and decomposing so that the nitrogen is returned to the soil
• they are not left to die so the nitrogen isnt returned to the soil
• overtime this reduces the nitrogen content of the soil
• which can lead to deficiency diseases and poor crop growth

Question 20

what are the two ways that farmers are increasing the amount of nitrates in the soil to help their crops grow better

Answer 20

• crop rotation

- and fertilisers

Question 21

how does crop rotation increase the nitrogen content of the soil

Answer 21

• instead of growing the crop in a field year after year
• different crops are gown each year in a cycle
• the cycle usually includes a nitrogen fixing crop
• which helps put nitrates back into the soil for another crop to use the following year

Question 22

how do fertilisers increase the nitrogen content of the soil

Answer 22

• spreading animal manure or compost on fields recycles the nutrients left in plant and animal waste
• and returns them to the soil through decomposition
• artificial fertilisers containing nitrates and other mineral ions can also be used
• but these can be expensive