Nutrient Cycles

Question 1

Role of saprobionts in recycling chemical elements

Answer 1

Break down DOM
By secret wing enzymes for extracellular digestion
Absorbs soluble needed nutrients and releases mineral ion (phosphates)

Question 2

What is a mycorrhizae

Answer 2

Symbiotic association between fungi and plant roots

Question 3

Role of mycorrhizae

Answer 3

Fungi act as an extension of plants roots to increase SA, this increases absorption of water and ion
In return the fungi revives organic compounds (carbs)

Question 4

Role of bacteria in N fixation

Answer 4

N2 (gas) converted to ammonia (NH3), this forms ammonium ions, by nitrogen fixing bacteria (in root nodules)

Question 5

Role of bacteria in ammonification

Answer 5

DOM is broken down/decomposed
-converted into ammonia to form ammonium ions in the soil
-by saprobiants

Question 7

Role of bacteria in nitrification

Answer 7

Ammonium ions in soil are converted to nitrites and then nitrates via 2-step oxidation.

-by nitrifying bacteria in aerobic condition

Question 8

Role of bacteria in denitrification

Answer 8

Nitrates in the soil are conveyed into N gas (reduction)

By denitrifying bacteria (anaerobic condition)

Question 9

Describe N cycle

Answer 9

N2 (gas in atmosphere )

Nitrogen fixation (N-fixing bacteria)
Produces ammonia

Ammonification (saprobionts)
Producing ammonium

Nitrification (Nitrifying bacteria)
Produce nitrites and nitrates

Dentrification: (denitrifying bacteria)
Producing N2 (gas)

Question 10

Why does ploughing create nutrients in the soil

Answer 10

More nitrification,
Less N being conveyed to gas (denitrification)

Question 11

Describe P cycle

Answer 11

Phosphate ions in rocks are released by erosion/weathering

-the ions are taken up by producers (plants) and incorporated into their biomass. (Uptake is increased by mycorrhizae)

-P ions transferred though food chain

-some P ions lost in waste products (faces)

-saprobionts decompose organic compounds releasing P ions

Question 12

Why are fertilisers used

Answer 12

To replicate N or P ions lost when plants are harvested and livestock removed

Ions removed from soils and into biomass can’t be released back into the environment

So improve efficiency to increase yield

Question 13

Difference between artificial and natural fertilisers

Answer 13

Natural:
-organic
-ions released during decomposition by saprobionts

Artificial:
-contain inorganic compounds of N, P and K

Question 14

Environmental issues arising from fertiliser use

Answer 14

P and N ions dissolve in water, leaching into rivers

This leads to eutrophication