Nutrient Cycles

Question 1

What are the common features of nutrient cycles?

Answer 1

• living organisms require nutrients from envi. for growth + other processes
• nutrients are returned to envi. when organisms produce waste or die + decompose bc waste products + dead organisms are digested by microorganisms
• products of decomposition are used by plants as nutrients in soil which sustain organisms in higher trophic lvls

Question 2

What are the 2 examples of nutrient cycles?

Answer 2

• the nitrogen cycle
• the phosphorous cycle

Question 3

Why do animals + plants require nitrogen?

Answer 3

• to produce biological molecules such as proteins, nucleic acids (DNA + RNA) + ATP
• however, they can’t access atmospheric N2 bc it contains a triple bond
• so microorganisms are needed to convert it into nitrogen containing compounds that they can absorb

Question 4

What are the 4 key processes in the nitrogen cycle, that are carried out by diff bacteria?

Answer 4

• ammonification
• nitrification
• nitrogen fixation
• denitrification

Question 5

What is the definition of ammonification?

Answer 5

• saprobionts produce ammonia from organic nitrogen-containing compounds which forms ammonium ions in soil

Question 6

What is the definition of nitrification?

Answer 6

• nitrifying bacteria converting ammonium ions in soil into nitrites + then to nitrates

Question 7

What is the definition of nitrogen fixation?

Answer 7

• nitrogen-fixing bacteria, living in legume root nodules, converting atmospheric nitrogen into nitrogen containing compounds

Question 8

What is the definition of denitrification?

Answer 8

• denitrifying bacteria converting nitrates in soil into atmospheric nitrogen

Question 9

Describe the nitrogen cycle.

Answer 9

• some atmospheric N2 is converted into nitrogen-containing compounds (ammonia/nitrates) by nitrogen fixing bacteria living in legume root nodules
• some reacts w nitrogen fixing bacteria in soil to form ammonium (NH4+) by ammonification
• nitrifying bacteria converts this ammonium to nitrites (NO2-) + then to nitrates (NO3-) by nitrification
• some nitrates are absorbed by active transport into plants + used to create biological molecules (AAs, ATP, DNA)
• animals then eat plants + secrete waste (urine/faeces) containing nitrates. When animals + plants die, decomposers break down proteins + DNA in organic material to form ammonium (NH4+)
• other nitrates are converted back to atmospheric N2 by denitrifying bacteria in soil

Question 10

Why is denitrifying bacteria not wanted in agriculture?

Answer 10

• bc they cause nitrogen + nitrogen containing compounds in soil to be released back into atmo.
• bc bacteria is anaerobic (only occurs when O2 lvls in soil is low), farmers plough/aerate soil

Question 11

Why do animals + plants require phosphorous?

Answer 11

• to produce biological molecules such as phospholipids, nucleic acids (DNA + RNA) + ATP

Question 12

Describe the phosphorous cycle.

Answer 12

• phosphate ions (PO4^3-) in rocks are released + dissolved into water + soil by weathering
• they are then absorbed by plants via active transport + are incorporated into their biological molecules (DNA/phospholipids)
• they are transferred to animals when they consume + digest the plants
• phosphate ions from excretion of waste + remains from decomposition are released back into water + soil by saprobionts or converted into rocks by deposition
• phosphate ions trapped in sediment within water + soil can also create rocks over time

Question 13

What is the role of saprobiotic organisms in nutrient recycling?

Answer 13

• decomposition which ensures nutrients stored in dead organisms + waste products of organisms are recycled + made available to producers

Question 14

What are the 2 types of saprobiotic organisms?

Answer 14

• saprobionts
• mycorrhizae

Question 15

Describe the role of saprobionts in nutrient recycling.

Answer 15

• decomposers made up of fungi + bacteria secrete digestive enzymes onto dead organisms + waste material, which hydrolyses the biological molecules
• they then extracellularly digest the material + absorb the products (saprobiotic nutrition)

Question 16

What is mycorrhizae?

Answer 16

• the symbiotic relationship between plant roots + fungi

Question 17

Describe the role of mycorrhizae in nutrient recycling.

Answer 17

• fungi, which is composed of long, thin hyphae, inc SA for water + mineral ion absorption
• it acts like a sponge so holds water + minerals around plant roots = makes them more drought resistant + able to take up more inorganic ions
• fungi receives organic compounds (e.g. glucose) from plant in return

Question 18

Why are fertilisers needed in agricultural ecosystems?

Answer 18

• they replace minerals (e.g. nitrate + phosphate ions) lost from soil when crops + livestock are harvested + removed from nutrient cycles
• ensures crops + livestock continue to grow + inc in biomass so yields remain high, inc productivity

Question 19

What are the 2 diff types of fertilisers?

Answer 19

• natural fertilisers (dead organisms + waste materials: manure)
• artificial fertilisers (inorganic chemicals)

Question 20

What are the pros + cons of natural fertilisers?

Answer 20

• can improve soil structure = dec soil erosion + inc water holding ability of soil
• cheaper
• leaching less likely bc release of mineral ions into soil is slower
• nutrients present aren’t v concentrated so large amounts needed
• exact minerals + proportions can’t be controlled

Question 21

What are the pros + cons of artificial fertilisers?

Answer 21

• exact chemical composition is known + can control proportions of minerals applied
• nutrients present are concentrated so smaller amounts needed
• more water soluble so ions dissolve in water surrounding soil = large quantities washed away w rainfall = great impact on envi.

Question 22

What are the envi. impacts of fertilisers?

Answer 22

• leaching = when water soluble compounds (e.g. nitrogen containing fertilisers) are washed away by rainwater + into rivers + ponds which can lead to eutrophication

Question 23

What is eutrophication?

Answer 23

• when a body of water becomes enriched w nutrients causing excessive growth of aquatic plants + microorganisms that deplete the water’s O2 supply

Question 24

How does leaching + eutrophication affect the envi.?

Answer 24

• when nitrates leach from fertilised fields, it stimulates rapid growth of algae at surface of water [algal bloom]
• this blocks out sunlight so plants below can’t photosynthesis + so die
• decomposing bacteria in water feed on dead plant matter = inc in bacteria which all respire aerobically hence use up O2 in water
• eventually, fish + other aquatic organisms die due to a lack of dissolved O2 in water