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Biology OCR A A-level yr 12 > ecosystems > Flashcards

ecosystems Flashcards

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1
Q

what is an ecosystem?

A

interactions between living organisms in a defined area and the physical factors present

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2
Q

All ecosystems are dynamic. What does this mean?

A

means they are constantly changing due to living organisms present and the environmental conditions

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3
Q

what is a biotic factor?

A

living factor or once lived e.g competition for food, space, breeding. partners which can be within or between different populations

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4
Q

what is an abiotic factor?

A

non-living/physical factor e.g rainfall, temp

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5
Q

Describe the abiotic factor of light

A

In general, greater light availability, greater success of a plant species. However plants can cope with different light intensities e.g larger leaves, photosynthetic pigments which require less light or reproductive systems that operate only when light is at optimum

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6
Q

Describe the abiotic factor of temperature

A

temp effects enzymes controlling metabolic reactions. Plants and ectothermic animals develop rapidly in warmer temps. Temp change can affect migration, hibernation, dormancy, leaf fall and flowering

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7
Q

Describe the abiotic factor of water availability

A

In most plant and animal populations, lack of water leads to water stress and death. It can cause plants to wilt and water is required for photosynthesis. However xerophytes have developed ways to cope with water stress

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8
Q

describe the abiotic factor of oxygen availability

A

-In aquatic ecosystems it is beneficial to have fast flowing cold water as it contains high concentrations of oxygen. When water becomes too warm of the flow rate is too slow, oxygen concentrations drop which can lead to suffocation of aquatic organisms.
-In water logged soil, air spaces are filled with water, reducing oxygen availability for plants

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9
Q

Describe the abiotic factor of ephadic (soil) factors

A

Different soil types have different particle sizes which effects survival:
-clay: fine particles, easily water logged and forms clumps when wet
-loam: different sized particles, retains water but does not become waterlogged
-sandy: coarse, well separated particles that allow free draining. Sand soil doesn’t retain water and is easily eroded

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10
Q

What is a trophic level?

A

The trophic level of an organism is the position it occupies in a food web.

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11
Q

what is the first trophic level?

A

producer- an organism that converts light energy into chemical energy by the process of photosynthesis.

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12
Q

What are the subsequent trophic levels from the first?

A

consumers- organisms that obtain their energy feeding on other organisms. Animal that eats the producer is a primary consumer. Then secondary, tertiary, quaternary

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13
Q

Why do food chains rarely have more trophic levels from a quaternary consumer?

A

there isn’t sufficient biomass and stored energy left to support any further organisms

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14
Q

What are decomposers?

A

break down dead organisms, releasing nutrients back into the ecosystem.

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15
Q

what is biomass?

A

the mass of living material present in a particular place or organism. It can be equated to energy content

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16
Q

how do you calculate biomass at each trophic level?

A

multiply biomass the biomass present in each organism by the total number of the total number of organisms in that trophic level.

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17
Q

why do scientists calculate ‘dry mass’ present?

A

to measure biomass is to measure the mass of fresh material present so water content must be discarded as different amounts of water are present in different organisms resulting to unreliable results.

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18
Q

how is the ‘dry mass’ or an organism calculated?

A

organism must be killed and placed in an oven at 80 degrees for all water to evaporate- this point is indicated by at least two identical mass readings. Ton minimise destruction, a small sample is taken. This sample may not be representative of the population as a whole

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19
Q

units for biomass?

A

gm-2 for areas of land
gm-3 for areas of water

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20
Q

why can biomass be equated to energy content?

A

biomass consists of carbon compounds and carbon compounds are a store of energy.

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21
Q

units for energy available at each trophic level? and why?

A

(kJm-2yr-1) to allow changes in photosynthetic production and consumer feeding patterns throughout the year.

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22
Q

what is ecological efficiency?

A

the efficiency in which biomass or energy is transferred from one trophic level to the next.

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23
Q

why do producers only covert 1-3 percent of the sunlight into chemical energy?

A

-not all of the solar energy available is used for photosynthesis, 90 percent is reflected, some transferred through leaf and some is of unusable wavelength.
-other factors may limit photosynthesis e.g water availability
-some energy lost for photosynthetic reactions

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24
Q

what is gross production?

A

solar energy in plants converted in to organic matter. However, plants use some of this energy in respiration. The remaining is biomass, transferred to the next trophic level-net production

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25
Q

how can net production be calculated?

A

gross production- respiratory losses

26
Q

why do consumers only convert 10 percent of biomass into organic tissue?

A

-not all biomass is eaten e.g bones, plant roots
-some energy transferred to environment as metabolic heat as a result of movement and respiration
-some parts of an organism are eaten but indigestible and lost as faeces
-some energy lost in excretion material such as urine

27
Q

how can you calculate the ecological efficiency of energy/biomass transfer between each trophic level of a food chain?

A

(energy/biomass available after transfer divided by energy/biomass available before the transfer) times 100

28
Q

How does agriculture affect trophic level?

A

-In farming, there are three trophic levels: producers, primary consumers (livestock) and secondary consumers (humans)
-In cultivating plants there just two trophic levels. This is different to the natural ecosystems as plants and animals are provided with favoured abiotic conditions, competition removed and threat from predators removed

29
Q

what is the benefit to less trophic levels due to agriculture?

A

minimum energy is lost so more biomass transferred to humans

30
Q

what is decomposition?

A

chemical process in which a compound is broken down into smaller molecules or its constituent elements

31
Q

what is a decomposer?

A

an organism on and breaks down dead matter, turning organic compounds into inorganic ones available to photosynthetic producers

32
Q

Decomposers are saprotrophs, what does that mean?

A

they obtain their energy from dead or waste organic material

33
Q

What are detritivores?

A

organism involved in decomposition, which help to speed up the decay process by feeding on detritus- dead and decaying material. This increases surface area for decomposition to work on.

34
Q

why can’t nitrogen be absorbed from the atmosphere by plants?

A

nitrogen needs to be combined with hydrogen or oxygen

35
Q

why is nitrogen an essential element?

A

needed to make amino acids and proteins

36
Q

how does nitrogen fixation occur?

A

nitrogen fixing bacteria contains enzyme nitrogenase which combines atmospheric hydrogen (N2) with hydrogen (H2) to produce ammonia (NH3)- a form of nitrogen which can be absorbed by plants.

37
Q

where are nitrogen fixing bacteria found?

A

-can be found in free-living soil bacterium (Azotobacter)
-can be found inside rood nodules (Rhizobium)

38
Q

How is there a symbiotic relationship between nitrogen fixing bacteria living in root nodules and the plant?

A

-plant gains amino acids from nitrogen fixing bacteria
-bacteria gain carbohydrates produced by plant from photosynthesis which is an energy source.

39
Q

what is nitrification?

A

the process by which ammonium compounds in the soil are converted into nitrogen containing molecules which can be used by plants. Free living, nitrifying bacteria in the soil are involved.

40
Q

Describe the process of nitrification?

A

-oxidation reaction
-nitrifying bacteria (Nitrosomanas) oxidise ammonium compounds into nitrites (NO2-)
-Nitrobacter oxidise nitrites into nitrates (NO3-) - nitrate ions are very soluble

41
Q

What is denitrification?

A

-In the absence of oxygen (waterlogged soil), denitrifying bacteria can convert nitrates into nitrogen gas.
-anaerobic conditions, bacteria used nitrates as source of energy for respiration

42
Q

what is ammonification?

A

process by which decomposers convert nitrogen containing molecules in dead organisms into ammonium compounds

43
Q

Describe the carbon cycle?

A

-Producers convert carbon dioxide into organic materials by photosynthesis
-Consumers feed on plants, passing on carbon molecules
-both plants and animals respire, releasesing carbon dioxide into the atmosphere
-When plants and animals die, they decompose. The decomposers respire releasing carbon dioxide into the atmosphere
-Dead organic matter can accumulate forming fossil fuels or fossils which can be combusted, releasing carbon dioxide into the atmosphere

44
Q

How do carbon dioxide levels fluctuate?

A

-carbon dioxide levels are higher during night, where photosynthesis doesn’t occur
-carbon dioxide levels are lower during summer days, when photosynthetic rates are higher

45
Q

why has the global atmospheric carbon dioxide levels increased?

A

-deforestation
-burning fossil fuels

46
Q

what is succession?

A

the change in an ecological community over time

47
Q

what are the two types of succession?

A

primary and secondary

48
Q

what is primary succession?

A

occurs on an area of land that has been newly formed or exposed as bare rock. There is no soil or organic material to begin with.

49
Q

what is primary succession?

A

occurs on an area of land that has been newly formed or exposed as bare rock. There is no soil or organic material to begin with.

50
Q

What is secondary succession?

A

occurs on an area of land where soil is present but it contains no plant or animal species

51
Q

when does primary succession occur?

A

-volcanoes erupt, depositing lava (which solidifies into rock)
-sand is blown by the wind or deposited by the sea creating sand dunes
-silt and mud are deposited at river estuaries
-glaciers retreat depositing rubble and exposing rock

52
Q

What is each step in succession known as?

A

seral stage

53
Q

What can be identified at each serial stage?

A

-key species that change abiotic factors, especially soil, making it easier for subsequent existence of other species

54
Q

What are the main seral stages?

A

pioneer community, intermediate community and climax community

55
Q

Describe the pioneer community?

A

-begins by colonisation of inhospitable environment by organisms called pioneer species.
-species arrive as spores or seeds carried by wind or droppings of birds or animals
-first serial stage

56
Q

what are the adaptations of pioneer species allowing them to adapt to a bare environment?

A

-the ability to produce large quantities of seeds or spores
-seeds that germinate quickly
-ability to photosynthesis to produce their own energy
-tolerance to extreme conditions
-the ability to fix nitrogen from the atmosphere

57
Q

what is humus?

A

organic material which forms in soil when plant or animal matter decay

58
Q

Describe the intermediate community?

A

-when pioneer species die, humus is formed
-soil can support new species of plant known as secondary colonisers.
-Growth of plants will cause animals to colonise
-environmental conditions improve and tertiary colonisers arrive

59
Q

Describe climax community?

A

-community at stable state with little change over time
-few dominant and plant species

60
Q

At what stage of succession is biodiversity the highest?

A

mid-succession then the dominant plants and animals outcompete the others

61
Q

what is the plagioclimax?

A

the final stage when succession is stopped artificially

62
Q

why is agriculture one of the main reasons deflected succession occurs?

A

-grazing and trampling of vegetation by domesticated animals
-removing existing vegetation to plant crops
-burning as means of forest clearance

Biology OCR A A-level yr 12 (35 decks)

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