Nitrogen Cycle

Question 1

why are bacteria and fungi in soil decomposers?

Answer 1

they break down the dead remains and release the chemicals for the plants to use again - feeding and assimilation pass nitrogen (for example in protein molecules) along food chains

Question 2

nitrogen cycle process

Answer 2

1. nitrogen-fixing bacteria in the soil and roots of legume plants absorb nitrogen and reduce it to make ammonia. This process is called nitrogen fixation.
2. the ammonia is converted to nitrites and nitrates by nitrifying bacteria. this process is called nitrification.
3. plant roots can only absorb the nitrates. They are combined with carbohydrates (from
   photosynthesis) to form amino acids which are then made into proteins, and nucleotides which are joined to make DNA and RNA.
4. 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 (make) new proteins and DNA (assimilation).
5. when a plant or animal dies its tissues are decomposed by bacteria and fungi (saprotrophic feeding).
6. molecules containing nitrogen such as proteins are broken down by the bacteria and fungi and ammonia is released into the soil.
7. some nitrates are converted into N2 by denitrifying bacteria. this process is called denitrification.

Question 3

decomposition description

Answer 3

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

Question 4

decomposition bacteria involved

Answer 4

decomposing bacteria

Question 5

nitrification description

Answer 5

ammonia is converted to nitrites, and nitrates are converted into nitrates

Question 6

nitrification bacteria involved

Answer 6

nitrifying bacteria

Question 7

denitrification description

Answer 7

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

Question 8

denitrification bacteria involved

Answer 8

denitrifying bacteria

Question 9

nitrogen fixation description

Answer 9

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 10

nitrogen fixation bacteria involved

Answer 10

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

Question 11

where do some nitrogen fixing bacteria live?

Answer 11

in nodules on the roots of legume plants - the bacteria receive glucose from the plant, while the plant absorbs ammonia from the bacteria in the nodule

Question 12

what happens when the nitrogen fixing bacteria decomposes in the soil?

Answer 12

they make the soil much more fertile releasing ammonia which can be converted into nitrates - this is why farmers may rotate the crops they grow in each field