Biol4 - Nitrogen Cycle, Fertilisers, Diversity and Succession

Question 0

Decomposers?

Answer 0

Convert nitrogen in organic compounds (e.g. proteins) into ammonia

Question 1

Role of nitrogen-fixing bacteria?

Answer 1

N2 –> NH3

Convert nitrogen gas into ammonia

Question 2

Nitrifying bacteria?

Answer 2

~Convert ammonia into nitrite ions (NO2-) (nitrite bacteria)
~then nitrite into nitrate ions (NO3-) (nitrate bacteria)
~NH3 –> NO2- –> NO3-

Question 3

Denitrifying bacteria?

Answer 3

~NO3- –> N2 (g)
~convert nitrate ions into nitrogen gas
~use nitrates for respiration

Question 4

What is succession? (3)

Answer 4

~change in community over time
~due to change in environmental/abiotic factors
~which is caused by the presence and death of colonising species

Question 5

What is a climax community? (1)

Answer 5

~stable community/no further succession/final community

Question 6

Describe the main features of ecological succession starting with bare rock (7)

Answer 6

~pioneer species first
~lichens generally colonise first (i.e. Dry stone wall) as can survive hostile environment
~when lichens die they create humus and make environment less hostile
~allows other plants to colonise the changed environment, thick layer of soil now available
~more new species colonise changed environment i.e. less hostile environment with more niches, lichens eventually outcompeted
~e.g. of new species, small flowering plants, eventually shrubs + trees
~most likely climax community for UK = deciduous oak woodland

Question 7

How nitrates in soil are restored? (9)

Answer 7

~N2 (g) is converted into nitrates
~by atmospheric nitrogen fixation (i.e. lightening)
~or converted to ammonia by nitrogen fixing bacteria

~nitrogen containing organic material like proteins from dead animal/faeces
~are broken down by decomposers
~releasing ammonia from the organic material
~ammonia is converted to nitrites
~then the nitrite converted to nitrate
~by aerobic nitrifying bacteria

Question 8

Why do species in an environment going through succession change over time (2)

Answer 8

~initial species make environment less hostile (dead matter broken down to form soil)
~other species are better competitors/better adapted, outcompete other species

Question 9

If a pine tree has leaves all year, why is there a lower species diversity?

Answer 9

~only plants which photosynthesise with less light remain

Question 10

Why do areas of land with only one crop for agricultural farming have a low species diversity? (2)

Answer 10

~monoculture/fewer species

~removes habitats/fewer niches

Question 11

How ploughing fields can benefit crop plants? (5)

Answer 11

~ploughing allows oxygen to enter the soil
~which benefits nitrifying bacteria as they are aerobic
~ammonium ions (in the soil) are converted to nitrites and them nitrates by them
~nitrate is then absorbed by plants and used in nitrogen containing molecules e.g. DNA and amino acids
~this increases yield

Question 12

Give two advantages of using natural fertiliser produced in a digestor rather than an artificial fertiliser (2)

Answer 12

~increases organic content of soil

~production of artificial fertiliser is energy consuming

Question 13

Why crops with nitrogen-fixing bacteria on root nodules often grow better than other crops on soil with a low conc of nitrate ions? (2)

Answer 13

~Convert N2 to ammonium ions

~and produces amino acids which plants can use to form proteins (increases yield agriculture)