The Nitrogen Cycle Flashcards
what percentage of the atmosphere is nitrogen gas
78%
why cant nitrogen be directly used by animals and plants
- because nitrogen gas exists in the form N2
- and in this molecular compound form it is very unreactive
what is nitrogen needed for by organisms
making proteins for growth
what has to be done to the nitrogen gas in the air in order for plants to be able to use it
it needs to be turned into mineral ions such as nitrates
how do plants obtain nitrogen
- they absorb the mineral ions from the soil with their roots
- and use the nitrogen in the mineral ions to make proteins
how is nitrogen passed along the food chain
- it is passed in the form of proteins
- as animals eat each other
what are the types of decomposers and what do they do
- bacteria and fungi in the soil
- they break down proteins in rotting animals and plants
- and urea in animal waste
what is the result of the actions of decomposers
- they return nitrogen to the soil
- so the nitrogen in the organisms s recycled
what is nitrogen fixation
- the process of turning nitrogen gas (N2) from the air into nitrogen-containing ions in the soil
- which plants can use
what are the two main ways that nitrogen fixation occurs
- lightning
- nitrogen fixing bacteria in roots and soil
how does lightning contribute to nitrogen fixation
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
what are the four different types of bacteria involved in the nitrogen cycle
- decomposers
- nitrifying bacteria
- nitrogen-fixing bacteria
- denitrifying bacteria
what do nitrogen fixing bacteria bacteria do
- they turn atmospheric N2 into ammonia
- which forms ammonium nitrates
what do nitrifying bacteria do
- they turn ammonia in decaying matter int nitrites
- and then into nitrates
what do denitrifying bacteria do and where can you find them
- they turn nitrates back into nitrogen gas (N2)
- this is of no benefit to living organisms
- they are often found in waterlogged soils
other than the soil, where can nitrogen fixing bacteria live in
- nodules on the roots of legume plants
what do nitrogen fixing bacteria do on the nodules of roots of legume plants
- 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
what kind of relationship do plants and nitrogen fixing bacteria have
- a mutualistic relationship
- the bacteria get food (sugars) from the plant
- while the plant gets nitrogen ions from the bacteria to make into proteins
why does the nitrogen content of the soil decrease when crops are farmed and what can it lead to
- 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
what are the two ways that farmers are increasing the amount of nitrates in the soil to help their crops grow better
- crop rotation
- and fertilisers
how does crop rotation increase the nitrogen content of the soil
- 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
how do fertilisers increase the nitrogen content of the soil
- 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
