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A Level Biology OCR A UPDATED > 23 - Ecosystems > Flashcards

23 - Ecosystems Flashcards

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1
Q

What is ecology?

A

The study of interactions between organisms and their environment

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2
Q

What is a producer?

A

An organism that makes its own energy and biomass using sunlight

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3
Q

What is a habitat?

A

An area which a population of organisms lives in

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4
Q

What is a niche?

A

The part of a habitat which an organism is best suited to

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5
Q

What is an environment?

A

All the conditions that surround a living organism

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6
Q

What is a consumer?

A

Organism which gets its biomass from producers or other consumers by eating them

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7
Q

What is a community?

A

All the living organisms in a habitat

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8
Q

What is a trophic level?

A

The level at which an organism feeds in a food chain

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9
Q

What is a detritivore?

A

An organism which consumes dead or decaying matter

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10
Q

What is a decomposer?

A

An organism which breaks down organic matter

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11
Q

What is an autotroph?

A

An organism which produces its own biomass

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12
Q

What is an abiotic factor?

A

A non-living factor which affects organisms

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13
Q

What is a biotic factor?

A

A living factor which affects organisms

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14
Q

What are heterotrophs?

A

Organisms which get their biomass by consuming organisms from other trophic levels

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15
Q

What is a population?

A

All the organisms of one species living in a habitat at one time

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16
Q

What is a microhabitat?

A

A small part of a habitat with specific conditions

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17
Q

What is an ecosystem?

A

All living and non-living organisms in a habitat and their interactions

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18
Q

Can abiotic and biotic factors affect each other?

A

Yes- each can affect the other

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19
Q

What are the 3 types of change which can affect population size?

A
  1. Cyclic changes 2. Directional changes (non-cyclic and go in 1 direction) 3. Unpredictable changes (no rhythm or constant direction)
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20
Q

What are 2 examples of cyclic changes?

A

Tides and day length

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21
Q

What is an example of a directional change?

A

Erosion

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22
Q

What is an example of an unpredictable change?

A

Natural disaster such as a tsunami

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23
Q

What is constantly recycled within an ecosystem?

A

Matter

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24
Q

What is not recycled within an ecosystem and why?

A

Energy, as it flows through the ecosystem

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25
Q

Are all ecosystems the same size?

A

No- they can be as small as a bacterial colony or be the whole Earth

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26
Q

What are 5 examples of abiotic factors?

A
  1. Light 2. Water availability 3. Soil type 4. Oxygen availability 5. Temperature
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27
Q

What are the 3 main types of soil?

A
  1. Clay 2. Loam 3. Sandy
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28
Q

How would you quantitatively represent a food chain?

A

Use a pyramid of number

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29
Q

What is a drawback of pyramids of number?

A

They only give an accurate impression of the flow of energy if the organisms are of a similar size

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30
Q

What is a drawback of using a pyramid of biomass?

A

As organisms have to be killed and dried to construct one, the sample size tends to be small

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31
Q

What type of biomass is used in a pyramid of biomass and why?

A

Dry mass as fresh mass is unreliable and varies

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32
Q

A pyramid of biomass is always what shape?

A

A pyramid

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33
Q

How do you calculate ecological efficiency?

A

(Biomass of primary consumer/Biomass of producer) x 100

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34
Q

What is productivity?

A

The rate at which energy passes through each trophic level

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35
Q

What is gross primary productivity?

A

The rate at which plants convert light energy to chemical energy

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36
Q

What (roughly) is this planet’s gross primary productivity?

A

Around 8%

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37
Q

What are 3 reasons gross primary productivity is less than 100%?

A
  1. Only 2/3 of glucose is used to respire 2. Only 40% of light energy enters the light reaction for photosynthesis 3. Only half of light energy is used for glucose production
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38
Q

How do you calculate net production?

A

Net production = Gross production - Respiratory losses

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39
Q

What is net production?

A

The amount of organic matter remaining after respiration

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40
Q

What are 7 ways of increasing net production?

A
  1. Increase light availability 2. Ensure ideal temperature 3. Use insecticides 4. Use fungicides 5. Ensure maximum nutrient availability 6. Use herbicides 7. Use irrigation/drought resistant strains
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41
Q

What is biomass?

A

The amount of living material present in a particular place or within organisms

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42
Q

What units is biomass measured in?

A

Grams per metre squared (on land) or per metre cubed (in water)

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43
Q

What is ecological efficiency?

A

The efficiency at which biomass or energy is transferred between one trophic level and the next

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44
Q

What is nearly always true about biomass and trophic levels?

A

Increasing trophic levels generally see a decrease in biomass

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45
Q

What are 4 reasons consumers do not convert all the biomass from their food into their own organic tissue?

A
  1. Not all biomass of an organism is eaten (i.e. bones) 2. Some energy transferred to environment as metabolic heat due to movement and respiration 3. Some energy lost via excretory materials 4. Some parts of an organism eaten but indigestible
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46
Q

What are 4 ways humans can manipulate biomass transfer in agriculture?

A
  1. Create very simple food chains 2. Keep abiotic factors ideal 3. Minimise interspecific competition 4. Remove threat of predators
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47
Q

What 2 things are the most common decomposers?

A

Microscopic fungi and bacteria

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48
Q

What is saprobiotic nutrition?

A

Obtaining nutrients from dead organic matter using extracellular digestion.

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49
Q

What do decomposers release back into the environment?

A

Stored inorganic compounds and elements

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50
Q

How does saprobiotic nutrition work?

A

The extracellular enzymes break down complex organic molecules into simpler, soluble ones which the decomposer then absorbs

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51
Q

What is the primary difference between detritivores and decomposers?

A

Decomposers digest using extracellular enzymes, detritivores perform internal digestion

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52
Q

What are 2 examples of detritivores?

A

Woodlice and earthworms

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53
Q

What is detritus?

A

Dead and decaying organic matter

54
Q

What 2 classes of organic molecules have nitrogen as an essential component?

A

Amino acids and nucleic acids

55
Q

What is the chemical formula of a nitrite ion?

A

NO₂⁻

56
Q

What is the chemical formula of a nitrate ion?

A

NO₃⁻

57
Q

What is the chemical formula of an ammonium ion?

A

NH₄⁺

58
Q

Where do animals get their nitrogen from?

A

Their diet

59
Q

Can plants uptake nitrogen directly from the atmosphere?

A

No

60
Q

What 2 elements is nitrogen combined with for use by plants and animals?

A

Oxygen and hydrogen

61
Q

What organisms allow plants to take up nitrogen?

A

Bacteria in the soil

62
Q

Where do Rhizobium live?

A

In root nodules of leguminous plants

63
Q

Where do Azotobacter live?

A

Free living in the soil

64
Q

What are 3 examples of leguminous plants?

A
  1. Peas 2. Beans 3. Clover
65
Q

How do plants benefit from their symbiotic relationship with Rhizobium?

A

Get nitrogen for amino acids in the form of ammonia

66
Q

How do Rhizobium benefit from their symbiotic relationship with plants?

A

Gain carbohydrates from the plant for use as an energy source

67
Q

What are 2 examples of nitrogen-fixing bacteria?

A
  1. Rhizobium 2. Azotobacter
68
Q

What enzyme do nitrogen-fixing bacteria use?

A

Nitrogenase

69
Q

What is nitrogen fixation?

A

Where bacteria contain the enzyme nitrogenase which combines atmospheric nitrogen with hydrogen to form ammonia

70
Q

What is nitrification?

A

Conversion of ammonium compounds in the soil to nitrogen-containing molecules such as nitrates and nitrites

71
Q

Where do nitrifying bacteria live?

A

Freely in the soil

72
Q

What are 2 examples of nitrifying bacteria?

A
  1. Nitrosomonas 2. Nitrobacter
73
Q

How are nitrates converted back to nitrogen?

A

Denitrifying bacteria, which use the nitrates as respiratory substrates and release nitrogen

74
Q

In what type of soil would more denitrification occur and why?

A

Waterlogged or otherwise anoxygenic soil due to the greater presence of denitrifying bacteria

75
Q

What is a commercial example of nitrogen fixation?

A

Haber process

76
Q

What is ammonification?

A

Conversion of nitrogen-containing compounds in dead organisms back into ammonia

77
Q

What type of organisms do ammonification?

A

Saprobionts

78
Q

Why do many plants have a symbiotic relationship with mycorrhizal fungi?

A

They increase root surface area

79
Q

What does Nitrosomonas do?

A

Oxidise ammonia to nitrite ions, in order to release energy for them to live

80
Q

How is farmers plowing fields linked to nitrification?

A

The process is oxygenic, so farmers plow fields for aeration

81
Q

What does Nitrobacter do?

A

Oxidise nitrites to nitrate ions

82
Q

How can atmospheric nitrogen be converted directly to nitrates?

A

Lightning causing atmospheric oxygen and nitrogen to react

83
Q

What 2 enzymes are involved in ammonification?

A

Protease and deaminase

84
Q

What type of bacteria are nitrifying bacteria?

A

Chemosynthetic

85
Q

In what form does most nitrogen enter a plant and why?

A

Nitrates, as these are very soluble

86
Q

Are atmospheric CO2 levels higher in the day or night?

A

Night

87
Q

Why are atmospheric CO2 levels higher at night?

A

No photosynthesis taking place

88
Q

Why are CO2 levels lower in summer?

A

More photosynthesis taking place

89
Q

What are the 2 main reasons global CO2 levels have risen over the past 200 years?

A

Deforestation and burning fossil fuels

90
Q

How do the oceans make global warming a positive feedback loop?

A

Higher temperatures mean less CO₂ is dissolved in the oceans, so more is released into the atmosphere

91
Q

What are the two main types of succession?

A

Primary and secondary

92
Q

What is succession?

A

The process in which new plants and animal populations replace old plant and animal populations over time.

93
Q

What causes succession?

A

Changes to the abiotic factors within the environment causing the plant and animal species present to change

94
Q

What is primary succession?

A

Succession which occurs on land where no soil or organic matter was present originally

95
Q

What is secondary succession?

A

Succession which occurs on land where soil is present, but no plant or animal species

96
Q

What would be an example of an environment where secondary succession could occur?

A

The bare earth left after a forest fire

97
Q

What are 4 scenarios where primary succession would occur?

A
  1. Lava is deposited by volcanoes 2. Sand, blown by the wind or deposited by the sea, forming new sand dunes3. Silt and mud deposited at river estuaries 4. Glaciers retreat, depositing rubble and exposing bare rock
98
Q

What are the steps of succession known as?

A

Seral stages

99
Q

What are the 3 main seral stages? (in order)

A
  1. Pioneer community 2. Intermediate community 3. Climax community
100
Q

What types of conditions, stability and species are present during the first seral stages?

A

Instability, harsh conditions, low species diversity

101
Q

What types of conditions, stability and species are present during the later seral stages?

A

Greater stability, greater species diversity, less harsh conditions

102
Q

What are 2 examples of pioneer species?

A

Algae and lichen

103
Q

What species would be present during the pioneer community?

A

Pioneer species (colonisers)

104
Q

What are 5 adaptations of pioneer species?

A
  1. Ability to produce large amounts of seeds or spores 2. Tolerance to extreme environments 3. Ability to fix atmospheric nitrogen to add nutrients to soil 4. Ability to photosynthesise 5. Rapidly germinating seeds
105
Q

What are 2 methods by which pioneer species can be spread to an inhospitable environment?

A
  1. Spores or seeds carried by the wind from nearby landmasses 2. In bird or animal droppings
106
Q

What are 4 things which might alter the land of a habitat in succession?

A
  1. Fire 2. Disease 3. Agriculture 4. Grazing
107
Q

What happens in terms of succession after the land is altered?

A

Recolonisation

108
Q

What is humus?

A

The organic component of soil

109
Q

How is soil produced during primary succession?

A

Weathering of the rock produces the particles that form the basis of the soil, and when pioneer species die they release humus into the soil

110
Q

How and when do secondary colonisers arrive?

A

Via spores or seeds as soon as the soil contains enough nutrients

111
Q

What is an example of a secondary coloniser?

A

Moss

112
Q

When do tertiary colonisers arrive?

A

When environmental conditions improve enough

113
Q

What is a feature of tertiary colonisers?

A

They all have waxy cuticles, so can survive without an abundance of water

114
Q

What is an example of a tertiary coloniser?

A

Ferns

115
Q

Mass of what increases with each seral stage?

A

Organic matter

116
Q

How much change occurs in a climax community?

A

Very little over time

117
Q

What determines what species make up a climax community?

A

The climate

118
Q

What part of the succession process tends to have the most biodiversity?

A

The intermediate community

119
Q

Do animals also undergo succession?

A

Yes they do undergo succession in a similar way to plants

120
Q

What is a plagioclimax community?

A

One formed when succession is stopped artificially

121
Q

What are 3 ways in which plagioclimax occurs?

A
  1. Grazing and trampling of vegetation by domesticated animals 2. Removing existing vegetation to plant crops 3. Burning as a result of forest clearance
122
Q

What is the abundance of organisms in an environment?

A

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

123
Q

What 2 things increase the abundance of organisms in an environment?

A

Immigration and births

124
Q

What 2 things decrease the abundance of organisms in an environment?

A

Emigration and deaths

125
Q

What methods are used to measure distribution of species?

A

Line or belt transect

126
Q

What type of sampling are line and belt transects?

A

Systematic

127
Q

How do organisms tend to be distributed within a habitat?

A

Where biotic and abiotic factors favour them

128
Q

Given that transects cannot be used on animals, what method tends to be used to measure their abundance?

A

Capture-mark-capture-release

129
Q

What method is used to numerically measure biodiversity?

A

Simpson’s Index of Diversity

130
Q

What are the 6 steps of capture-mark-capture-release?

A
  1. Capture as many individuals as possible in a sample area 2. Mark or tag each individual 3. Release marked animals and give them time to reintegrate into the environment 4. Recapture as many as possible in sample area 5. Record number of marked and unmarked animals in sample 6. Use Lincoln index to measure population size

A Level Biology OCR A UPDATED (25 decks)

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