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OCR Biology A Level > 6.3 Ecosystems > Flashcards

6.3 Ecosystems Flashcards

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1
Q

Define habit

A

The place where an organism lives

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2
Q

Define population

A

A group of organisms of the same species living in the same area at a particular time

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3
Q

Define communitry

A

All the populations of different species living in a habitat

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4
Q

Define ecosystem

A

A physical area that includes all living and non-living components and their interactions

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5
Q

Define niche

A

The unique role of an organism in its environment

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6
Q

Define species

A

A group of similar organisms that can interbreed to produce fertile offspring

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7
Q

Define ecology

A

The study of interactions between living organisms and their environment

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8
Q

What are biotic and abiotic factors?

A

Biotic: Living factors of an ecosystem
Abiotic: Non-living factors

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9
Q

What changes can occur to an ecosystem? (6)

A
  • human activity
  • migration/species introduction
  • natural selection
  • climate change
  • natural disasters
  • succession
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10
Q

What is a dynamic ecosystem?

A

An ecosystem where changes are occuring all the time

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11
Q

Give examples of abiotic factors (8)

A
  • light intensity
  • wind velocity
  • rainfall
  • temperature
  • water availability
  • pH
  • oxygen availability
  • inorganic ion availability
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12
Q

Give examples of biotic factors (7)

A
  • competition (food, mates)
  • predators
  • grazers
  • disease
  • parasites
  • humans cutting down vegetation
  • reduced pollinators
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13
Q

Why is only some 1-3% of the sun’s light energy used by producers to make biomass (3)

A
  • 90% reflected by leaf (only some wavelengths (red/blue) used by chlorophyll
  • some light transmitted through the leaf without hitting a chloroplast
  • other limiting factors e.g. CO2 concentration, temperature
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14
Q

What are trophic levels?

A

Each stage of a food chain/web

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15
Q

What is a producer?

A

Autotrophic organisms that create organic molecles from inorganic molecules - the start of food chains

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16
Q

How to calculate ecological efficiency?

A

(Energy after transfer/energy after transfer) x 100
(Biomass after transfer/biomass before transfer) x 100

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17
Q

What is a consumer?

A

Organisms that derive energy from feeding on other organisms

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18
Q

What is a primary consumer?

A

Occupies the 2nd trophic level + gains energy from feeding on producers

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19
Q

What is a tertiary consumer?

A

Occupies the 4rd trophic level + gains energy from feeding on secondary consumers

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20
Q

What is a quaternary consumer?

A

Occupies the 4rd trophic level + gains energy from feeding on tertiary consumers

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21
Q

What is a secondary consumer?

A

Occupies the 3rd trophic level + gains energy from feeding on primary consumers

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22
Q

Why are quaternary consumers usually the last trophic level?

A

There is not sufficient biomass/energy left to support more organisms as energy is lost between each trophic level

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23
Q

Give key aspects of pyramids of numbers (6)

A
  • size of the bars is proportional to the number of organisms at each trophic level in the food chain
  • easiest to produce as just requires counting of organisms
  • producers alwasys at bottom
  • doesn’t account for size of organisams
  • not always pyramid shape
  • watch out for trees + parasites
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24
Q

Give key aspects of pyramids of biomass (4)

A
  • size of bars is proportional to biomass of each organism at each trophic level of food chain
  • biomass measured by dry mass for land gm-2 or seas gm-3
  • quick snapshot at particular time - not representative of seasonal changes
  • difficult to get data for as organisms must be killed but are quite accurate
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25
Q

Explain the proces of obtaining biomass weight for use in a pyramid of biomass (3)

A
  1. Organism collected from environment
  2. Dried in oven at 105 to evaporate water
  3. Weigh until mass remains the same
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26
Q

Give key aspects of pyramids of energy (3)

A
  • size of bars is proportional to the energy at each trophic level in the food chain
  • most accurate and measure energy (kJ m-2) as different biomass material may have different energy content
  • results more reliable than biomass
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27
Q

sExplain the proces of obtaining energy from an organism for use in a pyramid of energy

A
  1. Collect organism from environment
  2. Dry in oven at 105 to evaporate water
  3. Weigh unil mass remains the same
  4. Burn in O2 and record temp rise of fixed volume of water using calorimeter
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28
Q

Why does so little energy get passed between different trophic levels? (4)

A
  • lost to environment as heat due to respiration + movement
  • not all an organism is eaten e.g. bone, fur, feathers
  • some parts indigestible so are egested as feaces
  • lost in excretory materials e.g. urine
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29
Q

Why do secondary/tertiary consumers often access a higher % of energy avaialbe from the previous trophic levels compared to producers? (3)

A
  • they are consuming meat which is more digestible and contains mainy proteins and fats.
  • meat doesn’t contain cellulose, which can’t be digested by many secondary/tertiary consumers
  • althoug some animals have indigestible parts e.g. fur, feathers, scales, bones
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30
Q

Define gross primary production

A

The total solar energy converted into organic matter in producers - mainly dependant on how much photosynthesis is occuring

31
Q

Define net primary production

A

What’s left of the gross production after respiration has occured - biomass available for primary consumers

32
Q

How to calculate net primary production?

A

Gross primary production - respiratory loss

33
Q

Define net secondary production

A

What’s left of the biomass/energy in primary consumers after respiartion has occured - energy available for secondary consumers

34
Q

Define net tertiary production

A

What’s left of the biomass/energy in secondary consumers after respiartion has occured - energy available for tertiary consumers

35
Q

Give key aspects of agricultural ecosystems (3)

A
  • ecosystem of domesticated animals or plants for food consumption
  • humans try and get maximum energy transfer possible into food product
  • fewer trophic levels is key
36
Q

Compare natural and agricultural ecosystems (7)

A

Natural Ecosystem
- solar energy only
- low productivity
- more species diversity
- more genetic biodiversity
- nutrients recycled, little added
- population controlled naturally
- natural climax community

Agricultural Ecosystem
- solar + food + fossil fuel energy
- high productivity
- less species diversity
- less genetic diversity
- less recycled, more added e.g. fertilisers
- populations controlled with pesticides
- artificial community (no succession)

37
Q

How can a plant’s net production be lowered? (9)

A
  • eaten by pests
  • leaves fall off
  • low temperature
  • not enough minerals
  • not enough watrer
  • not enough light
  • too many minerals
  • high temperature
  • not enough CO2
38
Q

How can photosynthesis be controlled? (8)

A
  • temperature controlled by heaters + ventilation
  • optimum temp for enzyme activity in photosynthesis
  • light wave length controlled if dark
  • higher light intensity more light dependent reaction
  • cO2 controled by burning fuel
  • more CO2 fixed in calvin cycle
  • water supply controlled
  • use of fertilisers + pesticides
39
Q

How can productivity producing livestock be reduced (7)

A
  • predation
  • random reproduction
  • heat loss to environment
  • low food intake
  • not enough water
  • too much muscle movement
  • killed by disease
40
Q

How can livestock productivity be incresed? (7)

A
  • fencing in
  • selective breeding
  • temperature control
  • high protein meals
  • provide water
  • reduce movement
  • vaccination
41
Q

Define decomposition

A

Chemical process where larger organic molecules are broken down into smaller inorganic molecules

42
Q

Give key aspects of decomposers (5)

A
  • organisms that feed on and break down plant or animal matter
  • turn organic molecules into inorganic molecules for uptake by plants
  • include fungi + bactreria
  • saprotrophs obtain energy from dead or waste organic material
  • extracellular digestion means enzymes are secreted outside cells
43
Q

Give key aspects of detritivores (5)

A
  • organisms that feed on dead and decaying material
  • break down into smaller pieces of organic material
  • increase surface area for decomposers
  • speed up decomposition
  • perform internal digestion
44
Q

Why are there short term fluctuations in atmoshperic CO2? (3)

A

Photosyntheis removes CO2 from the atmosphere and respiartion adds CO2 to the atmosphere
- reduced CO2 concentration during the day as photosynthesis rate is higher than repsiration rate
- increased CO2 concentration during the night as photosynthesis rate is lower than repsiration rate

45
Q

What biological molecules contain nitrogen? (6)

A
  • amino acids
  • proteins
  • nucleotides
  • DNA
  • RNA
  • ATP
46
Q

Why does nitrogen fixation have to occur? (3)

A
  • N2 in the air can’t be accessed by plants
  • it has to be fixed into the soil by nitrogen fixing bacteria
  • so it becomes NH4+ which plants can use
47
Q

Give key aspects of azotobacter (3)

A
  • free living nitrogen fixing bacteria
  • in the soil
  • convert N2 to NH4+ using nitrogenase enzyme
48
Q

Give key aspects of rhizobium (3)

A
  • nitrogen fixing bacteria
  • in root nodules of leguminous plants
  • mutualistic symbiotic relationship
  • rhizobium gain carbs from plant for respiration
  • convert N2 to NH4+ using nitrogenase enzyme
49
Q

Give key aspects of nitrifying bacteria (3)

A

Nitrosomonas - oxidise ammonium compounds into nitrites
Nitrobacter - oxidise nitrites into nitrates
- nitrates are highly soluble and are the form of which more nitrogen enters a plant

50
Q

How else can nitrogen be fixed?

A

Non-living nitrogen fixation - Elecetrical energy in lightning combines oxygen and nitrogen in air to form nitrites + nitrates

51
Q

Give key aspects of denitrification

A

Denitrifying bacteria converts nitrates back into nitrogen gas
- happens in anaerobic conditions - waterlogged soil
- bacteria use nitrates as an energy source creating nitrogen gas

52
Q

Give an overview of ammonification (2)

A
  • caused by decomposers/saprotrohps e.g. bacteria + fungi
  • N2 in organic molecules into NH4+ & NH3
53
Q

Give an overview of nitrogen fixation (2)

A
  • caused by nitrogen fixing bacteria (rhizobium + azotobacter)
  • N2 to NH4
54
Q

Give an overview of nitrification (2)

A
  • caused by nitrifying bacteria (nitrosomonas + Nitrobacter)
  • NH4+ (ammonium ions) to NO2- (nitrites) to NO3- (nitrates)
55
Q

Give key aspects of primary succession (3)

A
  • starts with bare rock or sand
  • no soil or organic material present to begin with
  • could occur after volcanic eruption, earthquake, retreating glacier etc
55
Q

How does ploughing fields increase plant growth? (6)

A
  1. Oxygen enters the soil
  2. Nitrifying bacteria respire
  3. Ammonium to nitrite
  4. Nitrite to nitrate
  5. To make protein
  6. Leading to growth
55
Q

Give an overview of denitrifcation (3)

A
  • caused by denitrfying bacteria
  • NO3- (nitrates) to N2 (gas)
  • only in anaerobicconditions (water logged)
56
Q

How can adding manure increase crop yield? (5)

A
  1. Ammonium ions made from decomposition of manure containing proteins
  2. Ammonium ions converted into nitrate ions
  3. By nitrifying bacteria
  4. Nitrate ions taken up by plants
  5. Nitrogen needed for plant grwoth
56
Q

Define succession (5)

A
  • changes in abiotic factors
  • caused by decomposition of current species
  • to make the environment suitable for new species
  • while other species interspecifically out compete earlier species
  • repeated until a climax community is formed
57
Q

Give key aspects of secondary succession (2)

A
  • starts with a thin layer of soil
  • contains no plant or animal species
58
Q

What are sereal stages?

A

The steps of sucession
- pioneer community
- intermediate community
- climax community

59
Q

Explain the stages of succession

A
  1. Barren land/bare rock
  2. Pioneer community coloniers
  3. Secondary colonisers
  4. Tertiary colonisers
  5. Tertiart colonisers
  6. Scrubland
  7. Climax community
60
Q

Give key aspects of barren land/bare rock (2)

A
  • no soil or organisms
    e.g. retreating glacier, volcano lava cooling, sand dunes formation, mud forming in estuary
61
Q

Give key aspects of pioneer species (8)

A
  • suited to harsh environments
    e.g. lichens, xerophytes, algae, mosses
  • arrive as spores/ seeds carried by wind or animal passing through
  • die + decompose adding humus which contains nirates and can retain water
  • produce wind-despersing seeds that reach new locations
  • seeds germinate quickly
  • can photosynthesise to produce food
  • can fix nitrogen from the air
  • can cope with extreme abiotic conditions e.g. drough, heat, cold
61
Q

Give key aspects of tertiary colonisers (4)

A
  • as environmental conditions imrpove, new species of plants arrive
    e.g. ferns + grasses
  • rock continues to be eroded + mass of organic matter increases as organisms die
  • organisms decompose to contribute to nutrient rich soil
62
Q

Give key aspects of secondary colonisers (3)

A
  • arrive as spores + seeds
    e.g. mosses
  • die and decompose to form humus + soil
63
Q

Give key aspects of scrubland (2)

A
  • small trees + shrubs with many deep roots
  • change abiotic factors + may out compete many earlier species
64
Q

Give key aspects of climax communities (6)

A
  • stable community
  • little changes over time + no further succession
  • few dominant species
  • creation of many habitats, niches, food webs
  • abiotic conditions very stable
  • not always most biodiverse
65
Q

Which part of succession is most diverse?

A

Between intermediate and climax community

66
Q

What is deflected succession?

A

When succession is prevented by humans to stop climax communities being reached

67
Q

What is animal succession?

A

As plant species change more habitats and food for consumers are created

68
Q

What are plagioclimax communities?

A

Where a plant community is stopped or reaches its full climatic climax artifically by humans

69
Q

How can humans control succession? (5)

A
  • cutting down existing vegitation
  • burning for forest clearance
  • planting trees/crops
  • grazing/trampling by domesticated animals
  • harvesting planted crops

OCR Biology A Level (20 decks)

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