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A Level Biology > Module 6 - Chapter 23 Ecosystems > Flashcards

Module 6 - Chapter 23 Ecosystems Flashcards

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1
Q

Primary succession

A

The progressive placement of species on a newly formed or exposed area of uncolonised land where no previous organic material (such as soil) was present.

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2
Q

Give examples of starting land for primary succession

A

Newly formed sand dunes, bare rock, river deltas, glaciers

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3
Q

How does biomass change in primary succession? Why?

A

Increases because plants at later stages are larger than plants at earlier stages

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4
Q

Secondary succession

A

The replacement of one dominant type of species on land which has organic material (existing soil) but no living plant or animal species, some seeds may remain viable in the soil which plants can then develop from.

All previous living matter has been eradicated by natural disasters or biotic interventions such as forest fires.

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5
Q

Stage the seres of succession in order for primary succession

A

1) Barren land
2) pioneer community
3) intermediate community
4) climax community

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6
Q

Stage the seres of succession in order for secondary succession

A

1) intermediate community

2) climax community

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7
Q

How are primary and secondary succession different in the seres of succession? Why is secondary succession faster?

A

Primary succession begins from barren land and progresses to climax community.
Secondary succession begins with tertiary colonisers and scrubland in the intermediate community, biotic intervention occurs then recolonisation before reaching the climax community.

There are less seres in secondary succession so it’s quicker

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8
Q

Effects of the pioneer community in an uncolonised area

A
  • stabilise the environment
  • increase the humus content of the soil
  • increase nitrogen content of the soil by nitrogen fixing
  • increase soil depth (formation of soil)

These effects FAVOUR THE DEVELOPMENT OF NEW SPECIES

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9
Q

What is the pioneer community?

A

The pioneer species/colonisers are the first organisms to arrive at and colonise an area of newly formed or exposed land. They initiate the development of an ecosystem by changing the habitat and allowing different species to colonise.

This is possible due to their adaptations which are specialised to take advantage of the environment.

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10
Q

Adaptations of the pioneer community

A
  • Able to produce large quantities of rapidly germinating seeds to reproduce
  • are able to photosynthesise
  • contain nitrogen-fixing bacteria to enrich the soil with minerals
  • wind-pollination increases the likelihood of reproduction because insects are often not present.
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11
Q

How are the pioneer species introduced to the environment?

A

As wind-carried spores or seeds from nearby land or animals (including bird droppings)

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12
Q

Examples of pioneer species

A

Algae, lichen

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13
Q

What stages can the intermediate community be divided into?

A

Secondary colonisers, tertiary colonisers and scrubland

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14
Q

What do the secondary colonisers do?

A

Arise after the land is able to support their growth.

Soil is formed from weathered rock and the death of pioneer species enriches the soil when they decompose, releasing organic products (humus). The humus is able to sustain the secondary colonisers when they arrive as spores/seeds due to containing minerals, nitrates and retaining some water.

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15
Q

Example of secondary colonisers

A

Mosses

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16
Q

What do tertiary colonisers do?

A

Colonise the land once the conditions of the environment have improved to be able to supply the plants with sufficient water and minerals from the environment. they have a waxy cuticle to prevent water loss, maximising water retention.

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17
Q

Examples of tertiary colonisers

A

Grasses, ferns

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18
Q

How does scrubland arise?

A

Increased soil depth with a higher humus content is able to retain more water. These changes allow scrubland to grow in the more favourable conditions.

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19
Q

Examples of scrubland

A

Grasses, shrubs, small trees

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20
Q

Changes to the soil during succession

A
  • pH decreases as humus content increases (humus is acidic)
  • soil depth increases - due to weathering of rock
  • rocks broken down by root growth
  • soil aerated (by roots)
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21
Q

What is the climax community?

A

The final stage of succession

consists of the most dominant and well-adapted species for the environment so the community is stable (in equilibrium with the environment) and little change is observed over time.

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22
Q

When is biodiversity greatest during succession?

A

In mid-succession (intermediate community) before decreasing as the climax community develops.

The climax community has decreased biodiversity because the more adapted and dominant species outcompete the earlier pioneer and secondary colonisers.

the pioneer communities are often less stable because they are subject to greater succession.

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23
Q

Example of climax community

A

Woodland

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24
Q

What is deflected successsion?

A

When human activities prevent the climax community from being reached by stopping the natural succession process. A subclimax (plagioclimax) is reached.
The environment is changed so a different end product is formed which is not part of the natural progression to the climax community.

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25
Q

What is a plagioclimax?

A

A stage in succession when the natural climax community is prevented from forming (an artificial climax)

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26
Q

Example of a plagioclimax

A

Heathland

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27
Q

ways in which deflected succession could be caused?

A

grazing of animals - eating/trampling of seedlings of shrubs and trees prevents the development of grassland to scrubland

mowing of grass

application of fertiliser

humans burning forests to clear land - destroying the climax community and scrubland develops

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28
Q

what is autogenic succession?

A

when the changes to the environment are brought about by the plants themselves

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29
Q

what is allogenic succession?

A

when changes to the environment are brought about by external factors, e.g. rising sea level caused by flooding

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30
Q

definition for ecosystem

A

a defined area and all of the communities within it. consists of abiotic and biotic components and encompasses all of their interactions

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31
Q

definition for a habitat

A

an organism’s place of residence

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32
Q

definition for a population

A

a group of individuals of the same species which occupy a particular habitat

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33
Q

definition for a community

A

a collection of different populations which occur together in both space and time

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34
Q

definition for an environment

A

the set of conditions that surround a community and encompasses their abiotic and biotic environments

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35
Q

list some abiotic factors

A

light, temperature, water, oxygen, edaphic (soil) factors, pH

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36
Q

list some biotic factors

A

competition, prey, predators, mutualism, mates, parasitism

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37
Q

what are plants unable to do which animals can?

A

locomotion to find shelter, water, food - plants can only move towards light

migrate - find alternative food

regulated body temperatures so they are less affected by external change

survive on different food sources

plants are more affected by abiotic factors because of this

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38
Q

what does photoautotrophic mean?

A

make own food from light - plants/producers

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39
Q

describe the stages of energy transfer for life on earth

A

1) light energy is absorbed by photoautotrophs and converted into chemical energy by photosynthesis
2) light energy is used to make organic compounds (e.g. sugars) from inorganic sources (e.g. CO2)
3) Heterotrophs ingest the organic compounds to get chemical energy (ATP)
4) when organic compounds are broken down by respiration, ATP is produced to fuel metabolic processes

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40
Q

what does heterotrophic mean?

A

obtain energy/ food by consuming producers/autotrophs

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41
Q

why is a pyramid of energy always a pyramid shape?

A

energy dissipates to the surroundings as the trophic levels increase

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42
Q

what is the difference between egestion and excretion?

A

excretion is the removal of waste products from cells which are products of metabolism (cellular waste) e.g. ammonia,

egestion is the removal of undigested food (fibre)

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43
Q

what percentage of energy is typically transferred from one trophic level to the next?

A

10%

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44
Q

what is the energy which isn’t lost (but is stored) by consumers used for?

A

the growth and replacement of cells/tissues, this forms the biomass

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45
Q

what is the process by which consumers obtain energy in a food chain?

A

feeding

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46
Q

what are the two ways in which biomass can be measured?

A

as dry mass and fresh (wet) mass

all samples must be collected from the same area

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47
Q

how do you measure dry mass?

A

1) the organism is killed
2) heated to 80C to evaporate all water (heated to constant mass)
3) a calorimeter is used to calculate the energy content

48
Q

using small samples for dry mass

A

small samples should be used to minimise destruction so dry mass may not be representative for the whole population (could be larger/smaller than average)

at least 1% of the sample should be used to reduce the effects of chance

49
Q

how do you measure fresh mass?

A

simply take the mass, this is unreliable though because the measurement includes water content which is variable in organisms

50
Q

what is biomass?

A

the mass of living organisms present in a particular place or in particular organisms and can be equated with energy (carbon containing compounds that store energy)

51
Q

what is the equation for calculating biomass at each trophic level?

A

biomass present in each organism x total number of organisms in trophic level

52
Q

what are the units for biomass of land?

A

g/m^2

53
Q

what are the units for biomass for water?

A

g/m^3

54
Q

what are the problems associated with a pyramid of biomass?

A

cannot account for seasonal change - not representative of the whole year

55
Q

what are pyramids of energy?

A

pyramids of energy represent the flow of energy through each trophic level over a specified period of time and provide a measure of productivity

56
Q

what are the units used in pyramids of energy?

A

KJm^-2y^-1

57
Q

what is a disadvantage of pyramids of energy?

A

don’t show the effects of decomposers (energy flow to decomposers)

58
Q

what is the equation for ecological efficiency?

A

energy or biomass available after transfer / energy or biomass available before transfer x 100%

59
Q

what is ecological efficiency?

A

the net production of new biomass at each level as a percentage of energy flowing through it (productivity)

60
Q

what is productivity?

A

the rate of generation of biomass in an ecosystem

61
Q

what are the types of primary production/productivity?

A

gross primary production and net primary production

62
Q

what is gross primary production (GPP)?

A

the amount of chemical energy as biomass that a producer creates in a given length of time

63
Q

what is net primary production (NPP)?

A

the amount of chemical energy that is not consumed by respiration,

64
Q

what is secondary production?

A

the generation of biomass by heterotrophic organisms (consumers)

65
Q

what is the equation for GPP?

A

the amount of energy it has - energy used to respire

66
Q

what is the equation for NPP?

A

NPP = GPP - respiration

67
Q

what is the equation for secondary production?

A

biomass generation - transfer of organic compounds between trophic levels by feeding

68
Q

how could one maximise production of animals being commercially farmed?

A
  • hormones and steroids part of diet

- selective breeding to produce breeds with higher growth rates

69
Q

how can energy losses be minimised in commercial animal farming for food?

A
  • limit exercise/ movement (small habitats)
  • limit heatloss by many being housed together
  • harvest animals when young and most of their energy is used for growth (and so is stored)
  • treatment with antibiotics to prevent loss of energy due to pathogens
70
Q

what happens to energy which reaches the producers but is not converted to growth?

A

light is absorbed by non-photosynthetic parts, light passes through the leaf - missing chlorophyll/chloroplasts

71
Q

what are detritivores?

A

heterotrophs which consume detritus.

they speed up the decaying process by breaking detritus into smaller organic material to increase SA for enzyme action and for decomposers to break down.

detritivores digest internally

72
Q

what is detritus?

A

dead and decaying material

73
Q

what are examples of detritivores?

A

earthworms, woodlice, dung beetles, millipedes

74
Q

what are decomposers?

A

saprotrophs/saprophytes which break down dead organic matter into soluble inorganic products which are then used by photosynthesising organisms.

decomposers secrete enzymes externally, the products are then absorbed and released back into the environment. this is saprophytic digestion

75
Q

what are saprophytes?

A

obtain energy from dead/waste material

76
Q

why are carbon dioxide levels higher in winter than summer?

A

summer has higher temperature so increased rate of reaction of photosynthesis which uses CO2.

increased day length increases light intensity which also increases photosynthesis

77
Q

what are carbon sinks?

A

natural reservoirs which store carbon compounds. they absorb more carbon than they release as carbon dioxide.

78
Q

abiotic examples of carbon sinks?

A

soils, oceans

79
Q

biotic examples of carbon sinks?

A

forests, coral reefs

80
Q

positive feedback loop of global warming and oceans releasing carbon dioxide

A

global warming increases temperature, releasing CO2 from carbon sinks such as oceans (can’t remain dissolved in water), release of CO2 increases atmospheric CO2 levels - increasing global warming which continues to increase the ocean temperature

81
Q

examples of decomposers

A

saprophytic fungi and bacteria

82
Q

how can data on carbon dioxide levels over time be gathered?

A

carbon dating

83
Q

why is nitrogen required?

A

essential for making amino acids for protein synthesis and nucleic acids (nitrogenous bases in DNA nucleotides), ATP production

84
Q

why is nitrogen unable to be used by living organisms as it is?

A

it’s inert and contains a triple bond

85
Q

what is nitrogen fixation?

A

when N2 from the atmosphere is combined with hydrogen to form ammonia.

86
Q

nitrogen-fixing bacteria examples

A

Azotobacter and Rhizobium

87
Q

what enzyme do nitrogen fixing bacteria contain?

A

nitrogenase, enzyme which combines N2 and H2

88
Q

what is Rhizobium?

A

nitrogen fixing bacteria, aerobic, lives inside root nodules (rhizomes), has a symbiotic mutualistic relationship with the plant - plant gains amino acids, Rhizobium gains carbohydrates produced from photosynthesis.

ammonia absorbed directly from bacteria not soil

89
Q

what is Azotobacter?

A

free-living soil nitrogen-fixing bacterium, requires aerobic conditions

90
Q

what is nitrification?

A

ammonium compounds are converted into nitrogen-containing molecules (nitrites and nitrates),

only occurs in well-aerated soil because involves oxidation

91
Q

nitrifying bacteria

A

Nitrosomonas, Nitrobacter, both aerobic and free living in the soil

92
Q

first step of nitrification?

A

Nitrosomonas converts ammonium ions to nitrites (NO2-)

93
Q

second step of nitrification?

A

Nitrobacter converts nitrites to nitrates (NO3-)

94
Q

why can nitrates be absorbed by plants but nitrites can’t?

A

nitrate ions are highly soluble

95
Q

why are some plants able to absorbed ammonia or ammonium ions instead of nitrates?

A

in anaerobic condition nitrification is difficult so nitrates can’t be produced

96
Q

what is denitrification?

A

nitrates are converted to nitrogen by denitrifying bacteria, anaerobic bacteria so only occurs in anoxic conditions, e.g. waterlogged soils

97
Q

how is nitrogen produced in denitrification?

A

nitrates are used by bacteria for energy for respiration (can be used instead of oxygen as an electron acceptor) and release nitrogen

98
Q

what is ammonification?

A

nitrogen-containing molecules are converted into ammonium compounds by decomposers in dead organisms, faeces and urine

99
Q

how can nitrification occur by non-living processes?

A

lightning to produce nitrates and Haber process to produce ammonia

100
Q

why is waterlogged soil a problem for plants?

A
  • lack of oxygen because oxygen dissolves in the water and can’t be taken in. this prevents ATP production in respiration which is needed for active transport and taking in nitrates
  • anaerobic conditions lead to nitrates being converted to nitrogen which can’t be assimilated by plants
101
Q

how can plants in waterlogged soils overcome problems?

A

can obtain nitrates by becoming carnivorous

102
Q

why do organisms need to obtain energy?

A

for metabolic processes: movement, active transport, thermoregulation, anabolic reactions (building molecules)

103
Q

to convert plant proteins to ammonia what enzymes are needed?

A

protease and deaminase

104
Q

what does a line transect involve?

A

laying a line along the ground and taking samples at regular intervals

105
Q

what does a belt transect involve?

A

two parallel lines are marked and samples are taken of the area between the specified points

106
Q

what type of sampling are line and belt transects?

A

systematic (non-random)

107
Q

why is systematic sampling advantageous over random sampling?

A

allows the study of how differing abiotic factors in different areas of the habitat affect the distribution of species

108
Q

what is abundance?

A

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

109
Q

equation for abundance (estimated number in population m-2)

A

number of individuals in sample / area of sample (m2)

110
Q

measuring animal abundance technique

A

capture-mark-release-recapture

111
Q

what is the Lincoln index for?

A

estimated population size after capture-mark-release-recapture

112
Q

Lincoln index

A

estimated population size = (no of individuals in first sample x no in second sample) / number of recaptured marked individuals

113
Q

simpson’s diversity index

A

D = 1 - sum (number of individuals of each species / total number of organisms in ecosystem) 2

114
Q

analysing diversity index answer

A

always between 0 and 1, 0 = no diversity, 1 = infinite diversity, higher= more diverse

115
Q

richness v evenness

A

richness = no of different species per sample in an area

evenness = relative abundance of each species in an area

A Level Biology (8 decks)

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