cycles

Question 1

what percentage does the atmosphere contain of nitrogen gas

Answer 1

79%

Question 2

how is nitrogen made available to living organisms

Answer 2

nitrogen fixation

-carried out in the soil by certain types of bacteria

Question 3

describe the steps of the nitrogen cycle

Answer 3

1) nitrogen fixation -nitrogen gasses in atmosphere are converted into ammonia by nitrogen fixing bacteria (found in the soil)

2)Nitrification -ammonia is converted into nitrites by bacteria and then nitrates by nitrifying bacteria

3)Assimilation -plants absorb nitrates from the soil ,using them to make proteins and other compounds .Animsla eat the plants and nitrogen moves through the food chain

4)Ammonification-when plants ,animals die , saprobionts break them down, releasing ammonia into the soil

5)Denitrification -some denitrifying bacteria in the soil convert nitrates into nitrogen gas which is released back into the atmosphere

-the bacteria be anaerobic and increase in number in waterlogged soils where a shortage of oxygen leads to reduction in aerobic bacteria

Question 4

describe nitrogen fixation

Answer 4

-nitrogen fixing bacteria are essential for maintaining soil fertility
-the bacteria is free living in the soil and fix nitrogen into ammonia

-their roots have nodules caused by nitrogen fixing bacteria

-the plant gains fixed nitrogen in the form of ammonia from the bacteria which is used to form amino acids and protein

-in return , the bacteria obtain carbodyftates and vitamins produced by the plant during photosynthesis

Question 5

describe nitrification

Answer 5

oxidation of ammonia ions in the soil into nitrites and then nitrates by nitrifying bacteria

-nitrifying bacteria are aerobic microorganisms

-ploughing aerates the soil providing oxygen for nitrifying bacteria , increasing their number and the amount of nitrate produced from ammonium ions

Question 6

what are the two groups of nitrifying bacteria

Answer 6

-one oxidises ammonium into nitrites

-another group nitrifying bacteria oxidase nitrites into nitrates

-nitrates are absorbed by plant roots by active transport and provide the source of nitrogen for the synthesis of proteins and nucleic acids

Question 7

where is nitrogen fixing bacteria found

Answer 7

in the soil