Nutrient Cycles (A Level)

Question 1

what are nutrient cycles?

Answer 1

natural processes that recycle essential elements between organisms an the envionment

Question 2

give two examples of nutrient cycles?

Answer 2

-nitrogen cycle
-phosphorus cycle

Question 3

where is nitrogen found?

Answer 3

as N2 gas in the atmosphere and in proteins/DNA of organisms

Question 4

what are the four stages of the nitrogen cycle?

Answer 4

nitrogen fixation, ammonification, nitrification, denitrification

Question 5

what is nitrogen fixation?

Answer 5

conversion of N2 gas into ammonium compounds by nitrogen fixing bacteria

Question 6

where are nitrogen fixing bacteria found?

Answer 6

in the soil and in root nodules of legume plants

Question 7

what is ammonification?

Answer 7

saprobionts convert dead organisms (proteins etc) and waste into ammonium compounds

Question 8

what is nitrification?

Answer 8

oxidation of ammonium to nitrites then to nitrates by nitrifying bacteria

Question 9

what conditions does nitrification require?

Answer 9

aerobic soil

Question 10

what is denitrification?

Answer 10

conversion of nitrate ions to nitrogen gas by denitrifying bacteria

Question 11

when does denitrification occur?

Answer 11

in anaerobic, waterlogged soil

Question 12

what are the pros and cons of nitrogen fixation?

Answer 12

+adds usable nitrogen to soil
-slow, depends on bacterial activity

Question 13

what are the pros and cons of ammonification?

Answer 13

+recycles nitrogen from waste/dead material
-slower in dry or cold soil

Question 14

what are the pros and cons of nitrification?

Answer 14

+produces nitrates easily absorbed by plants
-stops without oxygen

Question 15

what are the pros and cons of denitrification?

Answer 15

+prevents excess nitrate buildup
-removes nitrogen from soil, reduces fertility

Question 16

why do farmers use fertilisers?

Answer 16

to replace lost minerals and increase plant growth and yield

Question 17

what are the two types of fertilisers?

Answer 17

organic fertilisers and inorganic fertilisers

Question 18

what minerals do fertilisers mainly supply?

Answer 18

nitrates, phosphates and potassium

Question 19

what are the disadvantages of fertiliser use?

Answer 19

leaching, eutrophication and reduced biodiversity

Question 20

what farming practices increase crop yield?

Answer 20

fertilisers, crop rotation, ploughing to aerate soil, draining waterlogged soil

Question 21

why do organisms need phosphorus?

Answer 21

for AP, DNA, RNA, phospholipids, and bone formation

Question 22

in what form is phosphorus found in ecosystems?

Answer 22

as phosphate ions in rocks, soil and water

Question 23

what releases phosphate ions from rocks?

Answer 23

weathering and erosion of phosphorus containing rocks

Question 24

how do plants obtain phosphate ions?

Answer 24

by absorbing phosphate ions from soil via roots

Question 25

how do algae obtain phosphate ions?

Answer 25

by absorbing phosphate ions dissolved in water

Question 26

how do animals obtain phosphate ions?

Answer 26

by feeding on plants or other animals

Question 27

how is phosphorus returned to soil and water?

Answer 27

through decomposition of dead organisms and waste by saprobionts

Question 28

what can happen to phosphate ions in water over long timescales?

Answer 28

they form sediments, compressed into phosphorus containin rock again

Question 29

does the phosphorus cycl have a gas phase?

Answer 29

no - it has no gaseous form making it much slower than the nitrogen cycle

Question 30

why is the phosphorus cycle considered slow?

Answer 30

because most phosphorus is locked in rock and released only by weathering

Question 31

what role do mycorrhizae play in the phosphorous cycle?

Answer 31

fungi form mutualistic relationships with roots - they increase phosphate uptake for the plant in exchange for sugars

Question 32

how do phosphate fertilisers affect the phosphorus cycle?

Answer 32

they add phosphate ions to soil, increasing plant growth and crop yield

Question 33

what are the negatives of phosphate fertilisers?

Answer 33

leaching into water and eutrophication, leading to algal blooms and oxygen depletion

Question 34

what is eutrophication in relation to phosphates?

Answer 34

excess phosphates -> algal bloom -> less light -> plants die (no photosynthesis) -> saprobionts respire -> oxygen levels drop -> fish die

Question 35

how are phosphate ions recycled after decomposition?

Answer 35

saprobionts mineralise organic molecules, releasing inorganic phosphate ions back into soil/water

Question 36

what limits the rate of phosphorus cycling in ecosystems?

Answer 36

availability of weathered rock phosphates and soil phosphate levels

Question 37

why is phosphorus often a limiting factor for plant growth?

Answer 37

soil phosphate levels are naturally low and difficult to replenish

Question 38

why are microorganisms important in ecosystems?

Answer 38

they recycle chemical elements like phosphorus and nitrogen

Question 39

name two types of microorganisms involved in mineral cycling?

Answer 39

saprobionts and myccorhizal fungi

Question 40

what are saprobionts?

Answer 40

organisms that decompose dead and waste organic matter

Question 41

what are mycorrhizae?

Answer 41

symbiotic relationships between fungi and plant roots

Question 42

how do mycorrhizae help plants?

Answer 42

they increase root surface area, improving absorption of water and inorganic ions

Question 43

what do fungi gain from mycorrhizal relationships?

Answer 43

carbon compounds e.g. glucose from the plant

Question 44

why are saprobionts and mycorrhizae important for ecosystems?

Answer 44

they maintain nutrient cycles, ensuring elements like nitrogen and phosphorus are available for plants

Question 45

why are fertilisers used in agriculture?

Answer 45

to replace nutrients lost when crops and livestock are harvested and removed, maintaining soil fertility and productivity

Question 46

what are natural fertilisers made from?

Answer 46

organic matter:manure, compost, crop residues

Question 47

give two advantages of natural fertilisers?

Answer 47

slow nutrient release so less leaching improve soil structure and water retention

Question 48

give two disadvantages of natural fertilisers?

Answer 48

nutrients are less concentrated, so large amounts needed variable nutrient content, harder to control

Question 49

what are artificial fertilisers made from?

Answer 49

inorganic compounds in powders or pellets, e.g. ammonium nitrate

Question 50

give two advantages of artificial fertilisers?

Answer 50

concentrated nutrients, easy to apply precise nutrient content, controlled dosing

Question 51

give two disadvantages of artificial fertilisers?

Answer 51

highly soluble, so easily leached into water do not improve soil structure

Question 52

what is leaching?

Answer 52

mineral ions are washed from soil into rivers/lakes by rainwater

Question 53

why is leaching less likely with natural fertilisers?

Answer 53

nutrients are in organic matter and must be decomposed first so slower release

Question 54

what is eutrophication?

Answer 54

over enrichment of water with mineral ions, causing algal blooms and reduced oxygen