The Physical Environment (AS); Biogeochemical Cycles (Complete)

Question 1

Why are biogeochemical processes significant and what do they show?

Answer 1

Nutrients are processed, converted and recycled. Interlinked cyclical processes mean that small # of material continually recycled can support ecosystems over long time. Biogeochemical cycles show processes moving particular elements between their reservoirs in biosphere, atmosphere, hydrosphere and lithosphere

Question 2

What are the main reservoirs in the carbon cycle and why is there little changes to the amount of carbon?

Answer 2

In state of dynamic equilibrium so little/no change in # of carbon in each reservoir of cycle

Atmosphere- CO², methane, CO
Hydrosphere- hydrogen carbonate ions, dissolved CO²; surface waters 500 Gt + deep ocean 35,000 Gt
Biosphere- Carbs (cellulose,starch, etc), proteins,lipids; living organisms 470 Gt + 3700 Gt
Lithosphere- Carbonaceous rocks like limestone 20m Gt, fossil fuels 10,000 Gt

Question 3

How are photosynthesis and respiration processes in the carbon cycle?

Answer 3

Photosynthesis- captures light energy using pigments like chlorophyll. Makes CO² & H²O into carbs, could be converted into proteins & lipids

Respiration- Releases energy captured in photosynthesis to drive metabolic processes. Aerobic returns carbon to atmosphere as CO² & breaks down organic compounds more completely and w/ more energy than anaerobic- which allows some organisms to survive + use food sources in O²-deficient environments. usually returns CO² to atmosphere as methane.

Question 4

How are food webs, fossilisation and combustion processes in the carbon cycle?

Answer 4

Food webs- Some carbs, proteins,lipids made by plants are eaten by herbivores; may then be eaten by carnivores. Feeding relationships combine to make food webs
Fossilisation- Incomplete decomposition of dead organic matter, often in anaerobic conditions; can make substances forming long-term carbon stores (e.g fossil fuels) Organisms like molluscs make exoskeletons including calcium carbonate. Can make rocks like limestone- now contain most of carbon in lithosphere
Combustion- Burning of organic materials releases CO². Natural fires in forests may start by lightning

Question 5

How do humans affect the carbon cycle + examples?

Answer 5

Many human activities alter rates of movement of Carbon through cycle. Can unbalance natural dynamic equilibrium of cycle + change distribution of Carbon in reservoirs of cycle. Things humans affect:
- changes in photosynthesis
- changes in aerobic respiration
- changes in anaerobic respiration
- carbonic acid concentration in sea
- methane releases from fossil fuels
- combustion
- biomass movements

Question 6

How do anthropogenic changes in photosynthesis affect the carbon cycle?

Answer 6

• Deforestation ↓ movement of Carbon from atmosphere → biomass
• afforestation ↑ movement of carbon from atmosphere → biomass
• marine pollution w/ toxic materials ↓ phytoplankton populations =↓ absorption of dissolved CO² . Some naturally sink to seabed after dying,↑# of carbon in marine sediments.

Question 7

How do anthropogenic changes in aerobic respiration affect the carbon cycle?

Answer 7

Carbon in dead organic matter in soil → gradually released as CO² by aerobic respiration of soil organisms, esp bacteria + fungi
Ploughing ↑O² supply to decomposers living in soil so aerobic decomposition = more rapid. # of carbon in soil dead organic matter store ↓ & amount in atmosphere ↑.

Question 8

How do anthropogenic changes in anaerobic respiration affect the carbon cycle?

Answer 8

Absence of O² → respiration by anaerobic soil organisms releases methane. If released into atmosphere → gradually oxidised to CO²

Anaerobic environments made by human activities:
- rice paid fields
-landfill sites
- anaerobic sediments in reservoirs
- livestock intestines
Anaerobic environments destroyed by drainage:
- waterlogged fields
- marshlands
- peat bogs

Question 9

How do anthropogenic changes in the carbonic acid concentration in the sea affect the carbon cycle?

Answer 9

Humans don’t directly cause CO² to dissolve/ exsolve but their activities affecting concentration of CO² in atmosphere will after these processes, making a new equilibrium.
Dissolved CO² is in equilibrium w/ carbonic acid which dissociates, making hydrogen carbonate + hydrogen ions. Conc of hydrogen ions affects pH of sea = ↑ in dissolved CO² = ↓ pH of water. As atmospheric CO² conc ↑ dissolved CO² conc. ↑, so hydrogen ion conc. ↑→ sea more acidic.

Question 10

How do anthropogenic changes in combustion and methane releases affect the carbon cycle?

Answer 10

Combustion of fossil fuels & wood releases large # of CO² into atmosphere.

Methane may be released into atmosphere during fossil fuel extraction.

Question 11

How do anthropogenic changes in biomass movements affect the Carbon cycle?

Answer 11

Humans don’t directly move large # of carbon in biomass betw. areas, but they can produce local changes w/ environmental impacts:
- addition of compost/ mulch to improve soil fertility;
- deforestation & crop harvesting → reduced soil organic matter & soil erosion;
- movement of biomass into sea when sewage is discharged;
- movement of marine biomass → terrestrial system by fishing/aquaculture

Question 12

How can human impacts on the carbon cycle be counteracted?

Answer 12

A range of strategies of sustainable management:
- conservation of biomass carbon stores
- use of alternatives to fossil fuels
- Carbon sequestration
- carbon capture and storage (ccs)

Question 13

How does conservation of biomass carbon stores and the use of alternatives to fossil fuels counteract human impacts on the Carbon cycle?

Answer 13

Habitats like peat bogs & forests have huge # of Carbon - protecting these from exploitation/damaging land-use change = important to prevent even↑CO² releases

Renewable energy resources & nuclear power make ↓CO² emissions than fossil fuels.

Question 14

How does carbon sequestration counteract human impacts on the carbon cycle?

Answer 14

Large-scale tree planting could remove a lot of CO² from atmosphere & slow/reverse ↑CO² conc. Once tree reaches full size there’ll be no further net storage of Carbon but standing tree = carbon reservoir. If trees were harvested & kept as wood → replanting would make + Carbon storage as new tree grows.

Question 15

What is Carbon capture and storage (ccs)?

Answer 15

Involves capturing carbon, usually as CO² , so that its not released into atmosphere

Question 16

CCS: what is pre-combustion technology?

Answer 16

-Changing the fuel used, or the way it is combusted

Gasification → converts fuel like coal into gaseous hydrogen and CO²
CO² → can be removed for storage. Hydrogen → distributed for vehicle use/homes/ industry. When burnt, exhaust gas have water vapour but no CO²

Oxy-fuel combustion systems use pure oxygen so only CO² & water vapour are made. Water vapour can be removed by cooling gases so it condenses. Capture of CO² = easier as not mixed w/ other gases.

Question 17

CCS: What are the advantages & disadvantages of pre-combustion technology?

Answer 17

-It may be expensive & require development of new technology
-May also make removal of CO² easier and more efficient.
- May not be practical for many small sources like small vehicles
-Would be better if fuel was modified at large-scale facility where carbon is captured before fuel is used, so it wouldn’t release CO² when burnt

Question 18

CCS: what is post-combustion technology and the methods of it?

Answer 18

CO² can be removed from the exhaust gases of fossil fuel combustion w/ several methods;
- dissolving it in a solvent
- high pressure membrane filtration
- absorption/ description processes
- cryogenic separation
- graphene adsorption

None of these methods are fully developed & large scale costs = uncertain.

Question 19

How can Carbon be stored after it is captured?

Answer 19

-Most proposals involve storage underground in suitable geological structures like depleted aquifers, oil/gas fields.
-Can also be injected into oil reservoirs to provide pressure needed in secondary oil recovery
-Research shows CO² pumped into fractured basalt may react w/ minerals in rock, making solid carbonate materials

Question 20

Why is nitrogen essential for living organisms?

Answer 20

It is a component of many essential biological molecules

Question 21

What are the main reservoirs of nitrogen?

Answer 21

Atmosphere- N gas (N²)
Biosphere- Living organisms; DNA, proteins (cell membranes, hormones,etc)
Dead organic matter; proteins- release ammonium compounds as decompose
Lithosphere- Soil; ammonium compounds, nitrites, nitrates
Rocks; minerals with nitrogen
Hydrosphere- Dissolved nutrients & ammonium ions

Question 22

What is ionisation in the nitrogen cycle?

Answer 22

Processes like lightning & meteor trails give energy for atmospheric nitrogen & oxygen to react—> make oxides of nitrogen

Question 23

What is fixation in the nitrogen cycle?

Answer 23

Some micro-organisms can chemically reduce nitrogen to ammonia, which may be free-living bacteria in soil or may live symbiotically in root nodules of legumes

Question 24

How do food chains play a part in the nitrogen cycle?

Answer 24

Nitrogen passes between organisms as amino acids & proteins into food

Question 25

What is nitrification in the nitrogen cycle?

Answer 25

Involves the oxidation of ammonium ions to nitrites, then nitrates by nitrifying bacteria in soil

Question 26

What is denitrification in the nitrogen cycle?

Answer 26

Chemical reduction of nitrates in soil to nitrogen & nitrogen oxide gases (by denitrifying bacteria) reduces soil fertility- normally occurring under anaerobic conditions

Question 27

How does leaching occur in the nitrogen cycle?

Answer 27

High solubility of nitrates means they’re easily leached out of soils into water bodies- here they act as nutrients for aquatic plants & algae

Question 28

How does root absorption occur in the nitrogen cycle?

Answer 28

Plants absorb nitrogen as soluble ions, mainly as nitrates but also ammonium ions

Question 29

What is ammonification in the nitrogen cycle?

Answer 29

Amine groups in proteins are released as ammonium ions by action of bacteria, fungi and detritivores as they decompose dead organic matter

Question 30

What is the Haber process and how does it affect the nitrogen cycle?

Answer 30

-An industrial process for producing ammonia from nitrogen & hydrogen, with an iron catalyst at high temperature + pressure.
-This artificial fixation of atmospheric nitrogen to ammonia uses large # of energy. Ammonia then may be converted to nitrates
-Main purpose of the process is to manufacture agricultural fertilisers; may increase leaching problems like eutrophication

Question 31

How do agricultural practices affect the nitrogen cycle?

Answer 31

-Use of nitrate fertilisers may increase problems from leaching, like eutrophication if application is followed by heavy rain/fertilisers are close to rivers
-Drainage of fields makes soil more aerobic, increasing # of aerobic nitrifying bacteria & reduces # of anaerobic denitrifying bacteria
-Soil disturbance by ploughing increased decomposition rate of dead organic matter, releasing more nitrogen oxides—> atmosphere
-Leguminous plants (beans,peas) may be grown to increase levels of nitrogen compounds in soil; crops can then absorb this

Question 32

How does pollution (specifically combustion) affect the nitrogen cycle?

Answer 32

Nitrogen oxides (NOx) are released—> atmosphere by combustion processes & may increase quantity of nitrates washed into soil by rain

Question 33

How can combustion processes be controlled?

Answer 33

-Reduction in fossil fuel use to reduce NOx release; could be deliberate choice in attempting to develop sustainable lifestyles or caused by depletion of fossil fuel supply, move to other energy resources

-Adopting Circular Economy principles would result in use of more low-temp manufacturing processes, e.g use of polymers made by living organisms rather than high-temp processes w/ fossil fuel usage

Question 34

How can the release of NOx into the atmosphere be controlled?

Answer 34

Using post-combustion processes like catalytic converters & urea sprays.

Question 35

How can managing biological wastes reduce but also increase anthropogenic impacts on the nitrogen cycle?

Answer 35

-Decomposition of bio waste can release ammonium ions as amino acids in proteins are de-aminated
-Bio waste can be washed into water bodies by runoff/dumped deliberately. Ammonium compounds—> nitrites—> nitrates, causing eutrophication
-Enzymes made by bacteria remove amine groups (NH-²) which dissolve as ammonium ions
-This process can either cause issues or be useful, depending where it occurs

Question 36

How can organic fertilisers reduce anthropogenic impacts on the nitrogen cycle?

Answer 36

-Wastes like manure, sewage, food production waste can be used as organic fertilisers to increase nutrient & humus levels.
-May be ploughed into soil/applied to surface/composted aerobically/digested anaerobically before application as fertiliser.
-These processes reduce bulk of material, making application easier & produces fertiliser w/ better C:N ratio
-Composting & digestion reduce carbon content bc CO²/CH^4 gases are lost; more nitrogen-rich fertiliser is left

Question 37

How can soil processes manage anthropogenic impacts on the nitrogen cycle?

Answer 37

Farming practices can be changed to maximise advantageous processes increasing soil nitrate levels, e.g by-
-Cultivation of legume crops
-Crop rotation
-Minimal use of pesticides harming soil biota
-Control of nitrate leaching
-Not applying fertilisers when rainy/rain is likely
-Use of low-soluble fertilisers like urea
-minimal use of nitrate fertilisers where leaching into aquifers likely, etc.

Question 38

What biological functions does phosphorus have?

Answer 38

It’s a component of bones, ATP, DNA, RNA, cell membranes & proteins

Question 39

Why is phosphorus more likely to be a limiting factor on biological processes than other nutrients?

Answer 39

Most compounds of phosphorus have low solubility + there’s no gaseous reservoir of phosphorus

Question 40

How does absorption by roots occur in the phosphorus cycle?

Answer 40

-Plant roots absorb the phosphates they will use in metabolic processes
-They aren’t effective at absorbing phosphates so most plants have symbiotic relationships with mycorrhizal fungi, which have extensive networks of fungal hyphae in soil, increasing SA for phosphate absorption

Question 41

How is decomposition significant in the phosphorus cycle?

Answer 41

Breakdown of phosphorylated proteins in dead organic matter releases phosphates often more soluble by soil microbes, so can be absorbed by plants

Question 42

How is sedimentation significant in the phosphorus cycle?

Answer 42

Phosphorus in organisms that die & become incorporated into sediments may no longer be available to other organisms, like plankton (die & sink to ocean floor) This reduces productivity of surface waters of oceans bc phosphorus availability is often a limiting factor

Question 43

How is mountain building and weathering significant in the phosphorus cycle?

Answer 43

-Processes mobilising phosphorus & making it more available to living organisms are often slow.
-Phosphorus in marine sediments may not become available again until continental drift forms new mountain ranges & weathering of rocks releases phosphates

Question 44

How does mining of rocks by humans impact the phosphorus cycle?

Answer 44

-Most phosphorus in mined as calcium phosphate then treated to make ammonium phosphate—> more soluble
-In past, large accumulations of bird dropping were mined for ammonium phosphates they contained
These deposits built up in dry areas (eg. Peru, tropical islands). Most large guano deposits have been fully exploited

Question 45

How does anthropogenic fertiliser use impact the phosphorus cycle?

Answer 45

-Use of fertilisers mobilises phosphorus compounds—> environment in more soluble forms
=Increases crop production but can contribute to eutrophication

Question 46

How can human impacts on the phosphorus cycle be sustainably managed?

Answer 46

-Shortage of phosphates= limiting factor on crop productivity for large farmland areas. Availability of phosphates—> reduced by removal of biomass during harvesting & loss of phosphates w/ eroded soil. Maintaining future supplies of phosphates to compensate for losses by mining rocks= unsustainable
-Bio wastes should be used as fertilisers to maintain phosphates nutrient availability
-Crop breeding programmes—> increasing efficiency of phosphate absorption by crops