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Alevel Biology OCR > 6.3.1 - Ecosystems > Flashcards

6.3.1 - Ecosystems Flashcards

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1
Q

What is an ecosystem?

A

a defined area made up of living organisms that interact with eachother and factors present

  • range in size
  • are dynamic
    eg. rockpool, field, tree
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2
Q

What are abiotic factors?

A

non-living factors

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3
Q

What are biotic factors?

A 
living factors
(interactions between organisms)
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4
Q

What biotic factors affect ecosystems?

A

competition

  • food
  • territory
  • mates
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5
Q

What abiotic factors affect ecosystems?

A
  • light
  • temperature
  • water availability
  • oxygen availability
  • edaphic (soil) factors
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6
Q

How does light affect ecosystems?

A

-needed for photosynthesis

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7
Q

How does temperature affect ecosystems?

A
  • affects enzymes and ∴ metabolic reactions
  • plants and ecothermic animals develop quicker in warmer temps
  • temp changes trigger migration and hibernation
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8
Q

How does water availability affect ecosystems?

A
  • lack of water leads to water stress
  • lack of water causes plants to wilt (water is needed to keep cells turgid and plant upright) except xerophytes
  • needed for photosynthesis
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9
Q

How does oxygen availability affect ecosystems?

A
  • in aquatic ecosystems fast-flowing cold water is beneficial as it contains a high O2 conc
  • in water logged soil, air spaces are filled with water instead of oxygen
  • needed for aerobic respiration
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10
Q

How do edaphic (soil) factors affect ecosystems?

A

different soil types have different particle sizes (which effects which organisms can survive there)

  • clay - fine particles, easily waterlogged, clumps when wet
  • loam - diff particle sizes, retains water, not easily waterlogged
  • sandy - coarse/well separated particles, free draining, water not retained, easily eroded
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11
Q

What is biomass?

A

the mass of living material present in an organism

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12
Q

How is biomass transfer represented?

A

in food chains, food webs and pyramids of biomass

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13
Q

biomass at trophic level =

A

biomass in each organism x total no. organisms in trophic level

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14
Q

Why are producers not 100% efficient?

A

not all sunlight is converted into biomass

  • some light energy is reflected or transmitted through the leaf so isn’t all used for photosynthesis
  • other factors limit photosynthesis
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15
Q

Why isn’t all the biomass transferred between trophic levels?

A
  • not all biomass is eaten (eg, bones, roots, etc)
  • energy is lost to surroundings (as metabolic heat from movement and respiration)
  • some parts of food eaten are indigestible so are egested as faeces
  • some energy is lost as excretory materials (eg. urine)
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16
Q

ecological efficiency =

A

biomass transferred
_________________________ x 100
biomass before transfer (intake)

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17
Q

What is ecological efficiency?

A

efficiency which biomass is transferred from one trophic level to the next

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18
Q

How do human activities manipulate the transfer of biomass through ecosystems?

A

agriculture (environment is manipulated to favour crops being grown and animals being reared)

  • plants and animals are provided with abiotic conditions they need (eg. water, warmth)
  • competition from other species is removed (eg. using pesticides, fences to prevent predators)
  • agriculture shortens food chains (only 2/3 trophic levels) so less energy is lost
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19
Q

What is decomposition?

A

chemical process where a compound is broken down into smaller molecules so that they are more usable and can be returned to the environment

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20
Q

What is a decomposer?

A

an organism that feeds on and breaks down dead plant/animal matter

  • are saprotrophs (obtain energy from dead/waste materials)
  • digest food externally by secreting enzymes so that they can then absorb it
    eg. fungi, bacteria
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21
Q

What is a detritivore?

A

an organism that speeds up decay by feeding on detritus (dead, decaying matter) which breaks it into smaller pieces

  • digest internally
  • increases SA for decomposers to work on
    eg. woodlice, earthworms
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22
Q

What is the difference between decomposers and detritivores?

A
  • decomposers digest the dead matter externally (using enzymes) and then absorb it but detritivores digest it internally
  • decomposers are fungi and bacteria but detritivores are animals
  • detritivores break down the organic material into smaller pieces of organic material (increasing SA for decomposers) whereas decomposers break the organic material into inorganic material.
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23
Q

What is nitrogen fixation?

A

process where atmospheric nitrogen gas is combined with hydrogen to produce ammonia
N2 + H2 → NH3
-nitrogenase enzyme involved

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24
Q

How is nitrogen fixed by living organisms?

A
  • by nitrogen fixing bacteria in root nodules
    eg. Rhizobium
  • by nitrogen fixing bacteria in soil
    eg. Azotobacter
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25
Q

How is nitrogen fixed by non-living processes?

A
  • by Haber process

- by lightning

26
Q

What is nitrification?

A

process where ammonium compounds are converted into nitrites and nitrates
NH3 → NO2 - → NO3 -
-oxidation rxn (only occurs in well-aerated soil)
-uses nitrifying bacteria

two steps:

1) nitrifying bacteria (eg. Nitrosomonas) oxidise ammonium compounds into nitrites
2) nitrifying bacteria (eg. Nitrobacter) oxidise nitrites into nitrates

27
Q

What are the two steps of nitrification?

A

1) nitrifying bacteria (eg. Nitrosomonas) oxidise ammonium compounds into nitrites
2) nitrifying bacteria (eg. Nitrobacter) oxidise nitrites into nitrates

28
Q

What is denitrification?

A

process where nitrates in soil are converted into nitrogen gas in the absence of oxygen

  • only occurs in anaerobic conditions
  • denitrifying bacteria involved (use nitrates as energy source for respiration)
29
Q

What is ammonification?

A

process where nitrogen compounds in waste and dead organisms are converted into ammonium compounds
-by decomposers (eg. fungi, bacteria)

30
Q

Why is nitrogen important for living organisms?

A

is needed to make proteins and nucleic acids

31
Q

What stages occur in the nitrogen cycle?

A
  • nitrogen fixation (of nitrogen gas into ammonia)
  • nitrification (of ammonium compounds into nitrites and nitrates)
  • uptake and assimilation (of nitrates into plants)
  • transfer of nitrogen in food chain (from plants to animals)
  • death of plants/animals + ammonification (converted into ammonium compounds by decomposers)
  • denitrification (nitrates converted back into nitrogen gas)
32
Q

What stage of the nitrogen cycle is Nitrosomonas involved in?

A

nitrification

33
Q

What stage of the nitrogen cycle is Nitrobacter involved in?

A

nitrification

34
Q

What stage of the nitrogen cycle is Azotobacter involved in?

A

nitrogen fixation

free living in soil

35
Q

What stage of the nitrogen cycle is Rhizobium involved in?

A

nitrogen fixation

living in root nodules

36
Q

How do carbon dioxide levels increase in the atmosphere?

A
  • combustion of fossil fuels (releases CO2 that had been trapped in the Earth)
  • deforestation (less photosynthesis ∴ less CO2 taken in from atmosphere)
  • global warming (reduces carbon bank in oceans -higher temp = less gas dissolved in seas ∴ more CO2 released into atmosphere)
37
Q

What stages occur in the carbon cycle?

A
  • decomposition (releases CO2 into atmosphere)
  • photosynthesis (CO2 is used by plants)
  • plants are eaten by animals (carbon-containing compounds are eaten and made)
  • respiration (releases CO2 into atmosphere)
  • death and decay of plants and animals
  • combustion of fossil fuels (releases CO2 into atmosphere)
38
Q

What is succession?

A

the transition of an ecosystem over time

39
Q

What is a seral stage?

A

a step in succession

40
Q

What is primary succession?

A

the development of an ecosystem when plants grow where nothing has before (eg. on rock)

41
Q

What is secondary succession?

A

the development of an ecosystem when plants grow where soil is present but no species currently are
-ecosystem has previously been destroyed

42
Q

What are the stages of primary succession?

A
  • barren land (inhospitable environment)
  • pioneer community (land colonised by pioneer species)
  • intermediate community (secondary colonisers, tertiary colonisers + shrublands)
  • climax community reached (stable state)
43
Q

How do pioneer species colonise barren land (in primary succession)?

A
  • arrive as seeds/spores
  • produce a lot of seeds/spores
  • germinate rapidly
  • photosynthesise and fix nitrogen
  • are very tolerant to extreme living conditions
44
Q

Name an example of an organism in a pioneer community

A

lichen

45
Q

How does a pioneer community change to an intermediate community?

A
  • rock is weathered, producing particles that are a basis of soil
  • death/decomposition of pioneer species creates humus
  • this then supports new plant species that arrive as seeds/spores (secondary colonisers)
  • other plant species arrive (tertiary colonisers)
  • as rock is eroded more and more and soil becomes deeper and richer in nutrients, larger plants can grow
46
Q

Name an example of secondary colonisers

A

mosses

47
Q

Name two examples of tertiary colonisers

A

ferns

grasses

48
Q

How is a climax community reached (in primary succession)?

A

-community reaches a stable state where there is very little change and a few dominant plant species present

49
Q

Name an example of a climax community

A

woodland

50
Q

What happens in secondary succession?

A
  • land (in an intermediate or climax community) is altered (eg. by fire, disease, agriculture)
  • land is recolonised
  • succession occurs until a climax community is reached
51
Q

What is deflected succession?

A

succession where a climax community is stopped artificially, forming a plagioclimax
eg. for agriculture or conservation

52
Q

What is a plagioclimax?

A

the final stage of deflected succession

eg. farm field

53
Q

Why is animal succession slower than plant succession?

A

animals must move in from neighbouring areas

54
Q

What is distribution?

A

where organisms are located in an ecosystem

55
Q

How is the distribution of an organism within an ecosystem measured?

A

quadrats placed along a line/belt transect

56
Q

What is abundance?

A

the number of individuals of a species present in an area in a given time

57
Q

How is the abundance of plants in an ecosystem measured?

A

using quadrats

58
Q

estimated population of plants =

A

no. individuals
____________
area of sample

59
Q

How is the abundance of animals in an ecosystem measured?

A

using capture-mark-release-capture

  • capture and mark as many organisms as possible
  • release
  • allow time to distribute
  • recapture as many organisms as possible
  • record marked and unmarked organisms
  • use Lincoln index to find estimated population
60
Q

estimated population of animals =

Lincoln’s index

A

no. individuals in 1st sample x no. individuals in 2nd sample
____________________________
no. recaptured marked individuals

Alevel Biology OCR (26 decks)

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