Nutrients

Question 1

Nutrient cycles

Answer 1

Biogeochemical cycles involving elements essential to life

Question 2

Where are nutrient cycles found?

Answer 2

• in living tissue/products of a living organism (passed through food chain)
• in solution (taken up by plants and microorganisms)
• in the atmosphere
• in soil and rocks (temporarily unavailable to organisms)

Question 3

General pattern of nutrient cycles

Answer 3

• taken up by producers are simple, inorganic molecules
• producers incorporate the nutrient into complex organic molecules
• the producer is eaten- the nutrient passes onto the consumer and into the food chain
• when producers/consumers die, their complex molecules are broken down by saprobionts, that release the nutrient in its original, simple form

Question 4

Why is nitrogen necessary?

Answer 4

For the production of proteins and nucleic acids

Question 5

How does plants obtain nitrogen?

Answer 5

• Via nitrate ions (NO3-) actively transported from the soil

Question 6

How do animals obtain nitrogen

Answer 6

• obtained via consumption

Question 7

Nitrate ions

Answer 7

• INCREDIBLY soluble

* easily leach through soil, becoming unavailable to plants

Question 8

Nitrogen fixation

Answer 8

• N2 (g) is chemically unreactive- must be converted into absorbable nitrogen compounds
• carries out by nitrogenase-positive nitrogen fixing bacteria of either the i) free living variety or the ii) mutualistic variety

Question 9

Free living nitrogen fixing bacteria

Answer 9

• reduce N2(g) to ammonia (NH3)
• used to make amino acids
• nitrogen-rich compound release on decay

Question 10

Describe mutualistic nitrogen fixing bacteria

Answer 10

• live in legume root nodules
• synthesise amino acids
• obtain carbohydrates

Question 11

Equation for nitrogen fixation

Answer 11

N2 + 3H2 -> 2NH3

Question 12

Nitrification

Answer 12

• oxidation of ammonium ions to nitrites to nitrates

Question 13

Describe nitrifying bacteria

Answer 13

• free living
• chemoautotrophs (obtain energy from nitrification, because it is REDOX)
• aerobic -> aerated souls, oxygen water, drainage, ploughing

Question 14

Ammonification

Answer 14

• produces ammonia from organic nitrogen-containing compounds (fæces, urea, cadavers) containing proteins, nucleic acids and vitamins
• saprobionts

Question 15

Describe saprobionts

Answer 15

bacterial and fungal decomposers

Question 16

Denitrification

Answer 16

• causée by lack of air chambers- waterlogging - reduced O2 concentration
• changes microorganism populations
• more denitrifying bacteria -> anaerobic
• convert soil nitrates to N2 (g)
• reduces amount of nitrogen-containing compounds a plant can synthesis

Question 17

The phosphorous cycle

Answer 17

• no gaseous stage (no fixation) -> only found in mineral form
• weather and erosion of sedimentary rocks dissolve ions, allowing absorption and assimilation into biomass
• animals consume, excess excreted in waste
• some transported via waterways into waterbodies, forming sedimentary rocks (TAKES AGES)

Question 18

Why is phosphorus necessary?

Answer 18

• nucleic acids, phospholipids

Question 19

Where is phosphate found in nature?

Answer 19

(PO4)3- in sedimentary rock deposits

Question 20

Mycorrhizae

Answer 20

• associations between fungi (extensions - increase SA for more H2O + mineral absorption) and plant roots (provide organic compounds - sugars, AAs)
• mutualistic

Question 21

Why are fertilisers necessary?

Answer 21

• to stop soil mineral ion concentration getting dangerously low
• because they are constantly taken up by crops

Question 22

Why does agriculture cause the need for fertilisers?

Answer 22

• producers are harvested and removed; cannot decompose; less recycling

Question 23

Describe natural organic fertilisers

Answer 23

• dead and decaying plant and animal remains

* animal waste (manure, slurry, bone meal)

Question 24

Describe artificial inorganic fertilisers

Answer 24

• mines from rocks and deposits, converted and blended

* nitrogen, phosphorus and potassium are almost always present

Question 25

What gives the greatest long-term increase in productivity

Answer 25

Use of combination of natural organic and artificial inorganic fertilisers

Question 26

Higher nitrogen levels

Answer 26

Promote growth, which promotes photosynthesis

Question 27

Environmental issues of artificial inorganic fertilisers

Answer 27

• reduces species diversity (favours grasses, nettles and rapidly-growing species)
• leaching

Question 28

Leaching consequences

Answer 28

• pollutes watercourses

* can result in eutrophication

Question 29

Leaching process

Answer 29

• nutrients removed from soil due to rainwater dissolving soluble materials
• harmful is watercourses are potable

Question 30

Describe eutrophication

Answer 30

1) nitrate ion increases; no longer a limiting factor of plant and algal growth; populations proliferate
2) algae grow at the surface; algal bloom absorbs light preventing it from reaching the depths
3) light becomes limiting factor for plants and algae lower down; death
4) saprobionts proliferate on dead matter, creating an oxygen demand (nitrates are released from decaying organisms)
• oxygen concentration decreases; limiting factor for aerobic respiration; death
• less competition for anaerobic organisms
• nitrates and toxic waste make water putrid

Question 31

Give an example of toxic waste

Answer 31

Hydrogen sulphide

Question 32

What, other than artificial inorganic fertilisers, may result in eutrophication?

Answer 32

• organic manure
• animal slurry
• human sewage
• ploughing old grassland
• natural leaching