Nutrient Cycles

Question 1

Name the stages of the phosphorus cycle

Answer 1

• weathering
• run off
• assimilation
• decomposition
• uplift

Question 2

Why is the phosphorus cycle a slow process

Answer 2

• phosphorus has no gas phase so there is no atmospheric cycle
• most phosphorus is stored as PO3- 4 in rocks

Question 3

What happens during weathering and run off

Answer 3

Phosphate compounds from sedimentary rocks leach into surface water and soil

Question 4

Why is phosphorus important to living organisms

Answer 4

• Plants convert inorganic phosphate into biological molecules eg DNA, ATP, NADP
• is passed to consumers via feeding

Question 5

What happens ruing uplift

Answer 5

Sedimentary layers from the ocean are brought up to land over many years

Question 6

How does mining affect the phosphorus cycle

Answer 6

Speeds up uplift

Question 7

Describe the phosphorus cycle

Answer 7

• physical process of the climate (weathering) release phosphate ions from rocks
• phosphate ions pass to the environment, soil and water
• producers absorb phosphate ions from the environment
• transfer to consumer through food chain
• when producers and consumer dies, decomposition as the result of decomposers release phosphate ions into the environment
• phosphate ions are recycled and available for absorption by new gen of producers an transfer from producer to consumers

Question 8

4 main stages of nitrogen cycle

Answer 8

• nitrogen fixation
• ammonification
• nitrification
• denitrification

Question 9

Why can’t organisms use nitrogen directly from the atmosphere

Answer 9

N2 is very stable due to strong covalent triple bonds

Question 10

What happens during atmospheric fixation of nitrogen

Answer 10

• nitrogen gas (N2) converted to nitrogen containing compound (ammonia) by nitrogen fixing bacteria

Question 11

Role of nitrogen fixing bacteria

Answer 11

• Mutualistic nitrogen-fixing bacteria in nodules of legumes and free living bacteria in soil
• using the enzyme nitrogenase to reduce gaseous nitrogen into ammonia

Question 12

What is ammonification

Answer 12

• nitrogen containing compounds Brocken down
• converted to ammonia which form ammonium ions in the soil
• by saprobionts

Question 13

What is nitrification

Answer 13

Ammonium ion in soil —> nitrites —> nitrates
- by nitrifying bacteria
- in aerobic conditions - need o2

Question 14

What is denitrification

Answer 14

Anaerobic denitrifying bacteria convert soil nitrate back into gaseous nitrogen

Question 15

What conditions does denitrification usually occur in

Answer 15

Waterlogged skills as there is no o2 an conditions are anaerobic

Question 16

Significance of nitrogen to living organism

Answer 16

• plant roots Utah nitrates via active transport an use them to make biological compounds
• eg amino acid, NAD/NADP
• nucleic acid

Question 17

Role of mycorrhizae

Answer 17

• Mutualistic relationship between plant and fungus increases SA of root system
• increase uptake of water and mineral ions

Question 18

Benefits of planting a different crop on the same field each year

Answer 18

• nitrogen fixing crops eg legumes make soil more fertile by increasing soil nitrate content
• different crops have different pathogens
• different crops use different promotions of certain ions

Question 19

Two types of fertilisers

Answer 19

• Organic
• Inorganic

Question 20

Purpose of fertilisers

Answer 20

Increase gross productivity for higher yield

Question 21

Organic fertilisers

Answer 21

Decaying organic matter and animal waste

Question 22

Inorganic fertilisers

Answer 22

Minerals from rocks usually containing nitrogen, phosphorus, potassium

Question 23

Why at a certain point do fertiliser no longer increase crop yield

Answer 23

Conc of mineral ions limits the rate of photosynthesis so rate o growth cannot increase any further

Question 24

2 main environmental issues cause by fertilisers

Answer 24

Leaching and eutrophication

Question 25

Leaving

Answer 25

Nitrates dissolve in rainwater and runoff into water sources
- can prevent efficient o2 transport in babies

Question 26

What happens during eutrophication

Answer 26

• aquatic plants grow exponentially since nitrate level is no longer a lifting factor
• algal bloom on water surface preventing lit from reaching the bottom and plants die
• o2 levels decrease as population of aerobic saprobionts increase to decay dead matter so fish die
• anaerobic organisms reproduce exponentially and produce toxic waste making water putrid

Question 27

How can the risk of eutrophication be reduced

Answer 27

• Sewage treatment marshes on farms
• pumping nutrient enriched sediment
• using phosphate free detergent

Question 28

What are saprobionts (decomposers)

Answer 28

• release extracellur enzymes
• hydrolyse large complex materials in dead organisms into mall ones which they can absorb
• realises minerals in a form useable by plants