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Biology > 6.3.1 - Ecosystems > Flashcards

6.3.1 - Ecosystems Flashcards

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1
Q

Define ecology

A

The study of the relationships between organisms and their environment

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2
Q

What is an ecosystem ?

A

An ecosystem is made up of all the living organisms that interact with one another in a defined area

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3
Q

What is meant by ecosystems being dynamic ?

A

They are always changing

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4
Q

What are the two main groups of factors that affect an ecosystem ?

A

Abiotic and biotic factors

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5
Q

What are biotic factors ?

A
  • Living factors

- Such as organisms and the sizes of their populations

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6
Q

What are abiotic factors ?

A
  • The non living or physical factors

- Such as the amount of rainfall received

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7
Q

What do biotic factors refer to ?

A

They refer to the interactions between organisms that are living or have once lived

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8
Q

What do biotic factors often involve ?

A
  • They often involve competition

- Either interspecific or intraspecific

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9
Q

What do animals compete for ?

A
  • Food
  • Space
  • Breeding partners
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10
Q

List some of the main abiotic factors

A
  • Light
  • Temperature
  • Water availability
  • Oxygen availability
  • Edaphic (soil) factors
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11
Q

How are plants affected by light availability ?

A

Light is required for photosynthesis

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12
Q

What is the correlation between light availability and a plant species ?

A

In general, the greater the availability of light, the greater the success of a plant species

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13
Q

How do plants in low light adapt ?

A
  • They might have larger leaves

- They may develop photosynthetic pigments that require less light

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14
Q

What does temperature affect the most ?

A

Enzymes controlling metabolic reactions

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15
Q

When do plants develop more rapidly ?

A
  • In warmer temperatures
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16
Q

Define ectothermic animals

A

Animals that cant control their internal temperature, and so are more affected by the external environment

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17
Q

Define endothermic animals

A

Animals that control their internal temperature, and so are less affected by the external environment

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18
Q

What can changing temperatures in an ecosystem cause in animals ?

A
  • Migration

- Hibernation

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19
Q

What can changing temperatures in an ecosystem cause in plants ?

A

Leaf fall, dormancy and flowering

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20
Q

What does a lack of water lead to in most animals and plants ?

A

Leads to water stress, which will lead to death

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21
Q

What does water cause plants to do ?

A

It causes them to wilt

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22
Q

Why does water cause plants to wilt ?

A

Water is required to keep cells turgid and so keep the plant upright

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23
Q

Why is it key to have cold water in aquatic ecosystems ?

A

A fast flowing cold water system as it contains high concentrations of oxygen

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24
Q

What happens if the water becomes too warm or the flow rate becomes too slow?

A
  • Drop in oxygen concentration

- Can lead to the suffocation of aquatic organisms

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25
Q

How else is oxygen reduced for plants ?

A

In waterlogged soil, the air spaces between the soil particles are filled with water

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26
Q

What are the three main types of soil ?

A
  • Clay
  • Loam
  • Sandy soil
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27
Q

Describe clay

A
  • Fine particles
  • Easily waterlogged
  • Forms clumps when wet
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28
Q

Describe loam

A

This has different sized particles, retains water but does not become waterlogged

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29
Q

Describe sandy soil

A
  • coarse well separated particles
  • allow free draining
  • does not retain water
  • easily eroded
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30
Q

What is an ecological niche ?

A

It is a way of life that is unique to that species and describes its role in a community

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31
Q

What does an ecological niche describe ?

A
  • The conditions necessary for survival of the species

- The species’ role in the ecosystem

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32
Q

How are niche and habitat different ?

A

While many species may share a habitat, that is not true of a niche

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33
Q

What are food chains and food webs ?

A

These are diagrams that scientists use to show the transfer of biomass and therefore the transfer of energy

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34
Q

What is a trophic level ?

A

Each stage in the food chain

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35
Q

How many trophic levels do food chains normally have ?

A

5

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36
Q

Why do food chains rarely have more than 5 trophic levels ?

A

There is not sufficient biomass and stored energy left to support any further organisms

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37
Q

What is the order of levels in the food chain ?

A

Producer —> consumer —> secondary consumer —> tertiary consumer —> quaternary consumer

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38
Q

What are producers ?

A

An organism that converts light energy into chemical energy by the process of photosynthesis

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39
Q

What are consumers ?

A

Organisms that obtain their energy by feeding on other organisms

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40
Q

What are decomposers ?

A

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

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41
Q

How can food chains be presented diagrammatically ?

A

As a pyramid of numbers, with each level representing the number of organisms at each trophic level

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42
Q

Define biomass

A

The mass of living material present in a particular place or in particular organisms

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43
Q

How do you calculate biomass at each trophic level ?

A

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

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44
Q

How can this information be displayed diagrammatically ?

A

Pyramid of biomass

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45
Q

How do you measure biomass ?

A

Measure the mass of fresh material present

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46
Q

What do you have to take into account when measuring biomass ?

A

Water content must be discounted

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47
Q

What do scientists use to calculate biomass instead ?

A

You have to use the dry mass of the organism present

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48
Q

What are the problems involved with calculating dry mass ?

A

Organisms have to be killed in order to be dried

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49
Q

What are the units in measuring biomass ?

A
  • Grams per square metre (land)

- Grams per cube metre (water)

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50
Q

Why is biomass in each trophic level nearly always less than the trophic level below ?

A
  • When animals eat, only a small proportion of the food they ingest is converted into new tissue
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51
Q

What are the units for energy available at each trophic level ?

A

Kilojoules per metre squared per year

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52
Q

Why is energy worked out per year ?

A

To allow for changes in photosynthetic production and consumer feeding patterns throughout the year

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53
Q

What does a pyramid of energy show ?

A

The amount of biomass or energy converted to new biomass by each trophic level in a food chain

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54
Q

Define ecological efficiency

A

The efficiency with which biomass or energy is transferred from one trophic level to the next

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55
Q

What percentage of sunlight do producers turn into biomass ?

A

1% - 3%

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56
Q

Why is the percentage producers turn into biomass so low ?

A
  • Approximately 90% is reflected
    • Some is transmitted through the leaf
    • Some is of unusable wavelength
  • A proportion of the energy is lost, as it used for photosynthetic reactions
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57
Q

Define gross production

A

The total solar energy that plants convert to organic matter

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58
Q

How much of this energy is used in respiration for a plant ?

A

20%-50%

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59
Q

What happens to the energy that is not used in respiration ?

A
  • Converted into biomass

- This is the energy available to the next trophic level

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60
Q

What is the net production ?

A

Gross production - respiratory losses

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61
Q

Define primary production

A

The generation of biomass in a producer

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62
Q

Define secondary production

A

The generation of biomass in a consumer

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63
Q

How much of the biomass in the food of consumers is converted into organic tissue ?

A

10%

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64
Q

Why is the efficiency at the consumer level so low ?

A
  • Not all of the biomass of an organism is eaten, e.g. bones
  • Some energy os transferred to the environment as heat through movement and respiration
  • Some parts of an organism are indigestible, these parts are egested
  • Some energy is lost from the animal in excretion
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65
Q

What does agriculture involve ?

A

Agriculture involves the manipulation of the environment to favour plant species that we can eat and to rear animals for food

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66
Q

Give examples of how conditions are manipulated by humans

A
  • They are provided with abiotic conditions that they need to thrive such as watering and warmth
  • Competition from other species is removed
  • The threat of predators is removed
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67
Q

In a natural ecosystem what trophic level would humans occupy ?

A

The second, third or fourth trophic level

68
Q

What is the relation between agriculture and food chains ?

A

Agriculture creates very simple food chains

69
Q

What does a simple food chain ensure ?

A
  • Minimum energy is lost since there are fewer trophic levels
  • This ensures that as much energy as possible is transferred into biomass that can be eaten by humans
70
Q

What is decomposition ?

A

A chemical process in which a compound is broken down into smaller molecules

71
Q

What must happen to essential elements for them to be used by organisms ?

A

They must be processed into inorganic elements and compounds with a more usable form

72
Q

What is a decomposer ?

A

An organism that feeds on and breaks down dead plant or animal matter, thus turning organic compounds into nutrients

73
Q

How do decomposers obtain their energy ?

A
  • From dead or waste organic material

- They are saprotrophs

74
Q

What is this called (decomposer nutrition) ?

A

Saprobiotic nutrition

75
Q

How do decomposers digest this food ?

A
  • Externally by secreting enzymes onto dead organisms or organic waste matter
  • The enzymes break down complex organic molecules into simpler soluble molecules
  • The decomposers then absorb the molecules
76
Q

What are detritivores ?

A

They are another class of organism involved in decomposition

77
Q

What is a detritivores main role ?

A

They help to speed up the decay process by feeding on detritus (dead and decaying material)

78
Q

How do detritivores speed up the decay process ?

A

They break down the detritus into smaller pieces of organic material, which increases the surface area for the decomposers to work on

79
Q

Why is nitrogen essential ?

A

For making amino acids and nucleic acids in both plants and animals

80
Q

Where do animals get nitrogen from ?

A

The food they eat

81
Q

Where do plants get nitrogen from ?

A

From their environment

82
Q

What needs to happen to nitrogen for it to be used by living organisms ?

A

It needs to be combined with other elements such as oxygen or hydrogen

83
Q

What is the role of bacteria in the nitrogen cycle ?

A

Converting nitrogen into a form useable by plants

84
Q

What would happen to ecosystems without nitrogen ?

A

Nitrogen would become a limiting factor for those ecosystems

85
Q

Give two examples of nitrogen fixing bacteria

A
  • Azotobacter

- Rhizobium

86
Q

What do nitrogen fixing bacteria contain ?

A

The enzyme nitrogenase

87
Q

What is the role of the enzyme nitrogenase ?

A

It combines atmospheric nitrogen with hydrogen to produce ammonia

88
Q

Why is nitrogen converted to ammonia ?

A

This is because it can be absorbed and used by plants

89
Q

What is azotobacter an example of ?

A

Free living soil bacterium

90
Q

What is rhizobium an example of ?

A

Nitrogen-fixing bacteria that live inside root nodules

91
Q

What are root nodules ?

A

These are growths on the roots of leguminous plants such as peas and beans

92
Q

What kind of a relationship do the bacteria and plant have ?

A

A symbiotic mutualistic relationship

93
Q

How does the plant gain from its relationship with the bacteria ?

A

Amino acids which are produced by fixing nitrogen gas in the air into ammonia in the bacteria

94
Q

How does the bacteria gain from its relationship with the plant ?

A

Carbohydrates produced by the plant during photosynthesis

95
Q

What is nitrification ?

A

The process by which ammonium compounds in the soil are converted into nitrogen containing molecules that can be used by plants

96
Q

What is also involved in nitrification ?

A

Free living bacteria in the soil called nitrifying bacteria

97
Q

What kind of a reaction is nitrification ?

A

Oxidation reaction

98
Q

What are the two steps of nitrification ?

A
  • Nitrifying bacteria (nitrosomonas) oxidise ammonium compounds into nitrites
  • Nitrobacter oxidise nitrites into nitrates
99
Q

Why are nitrate ions able to enter a plant ?

A

They are highly soluble, and are therefore the form in which most nitrogen enters a plant

100
Q

What is denitrification ?

A

When denitrifying bacteria convert nitrates in the soil back to nitrogen gas

101
Q

When does denitrification happen ?

A

In anaerobic conditions such as waterlogged soils

102
Q

What is ammonification ?

A

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

103
Q

What are the main two reasons that CO2 levels fluctuate throughout the day ?

A
  • Photosynthesis

- Respiration

104
Q

How does photosynthesis affect CO2 levels ?

A
  • It only takes place in the light

- So during the day CO2 is removed from the atmosphere, not the night

105
Q

How does respiration affect CO2 levels ?

A

It is carried out during the day and the night, releasing CO2 constantly

106
Q

When are atmospheric CO2 levels higher ?

A

Atmospheric CO2 levels are higher at night than the day

107
Q

When do localised CO2 levels fluctuate ?

A

Seasonally

108
Q

What does CO2 levels fluctuating seasonally mean ?

A

CO2 levels are lower on a summers day than a winters day, as photosynthesis rates are higher

109
Q

What are the two main reasons that CO2 levels have increased greatly over the last 200 years ?

A
  • Combustion of fossil fuels
    • Released CO2 into the atmosphere from carbon that has previously been trapped for millions of years
  • Deforestation
    • Removed significant quantities of photosynthesising biomass.
    • Less carbon dioxide is removed from the atmosphere
    • Cleared forests are burnt, releases more CO2
110
Q

What is succession ?

A

A process by which ecosystems change over time

111
Q

Why does succession occur ?

A

As a result of changes to the environment, causing the plant and animal species present to change

112
Q

What are the two types of succession ?

A
  • Primary succession

- Secondary succession

113
Q

What is primary succession ?

A
  • This occurs on an area of land that has been newly formed or exposed such as bare rock
  • There is no soil or organic matter
114
Q

How is primary succession still taking place ?

A
  • Volcanoes erupt, depositing lava
  • Sand is blown by the wind to create new sand dunes
  • Silt and mud are deposited at river estuaries
  • Glaciers retreat depositing rubble and exposing rock
115
Q

What is secondary succession ?

A

This occurs on areas of land where soil is present, but it contains no plant or animal species

116
Q

What is each step of succession called ?

A

Seral stage

117
Q

Describe the brief outline of a seral stage

A

At each seral stage key species can be identified that change the abiotic factors, especially the soil, to make it more suitable for the subsequent existence of other species

118
Q

What are the main seral stages ?

A
  • Pioneer community
  • Intermediate community
    • Has many other seral stages within it
  • Climax community
119
Q

What does primary succession begin with ?

A

The colonisation of an inhospitable environment

120
Q

What is a pioneer species ?

A

A species that colonises an inhospitable environment

121
Q

How do pioneer species arrive ?

A

They arrive as spores or seeds carried by the wind from nearby land masses or sometimes by the droppings of birds or animals that pass through

122
Q

What are some adaptations of pioneer species ?

A
  • Ability to produce a large quantity of seeds or spores
  • Seeds that germinate rapidly
  • The ability to photosynthesise to produce their own energy
  • Tolerance to extreme environments
  • The ability to fix nitrogen from the atmosphere
123
Q

How is the basis of soil formed ?

A

The weathering of bare rock produces particles that form the basis of a soil

124
Q

How does the soil obtain organic products ?

A

When organisms of the pioneer species die and decompose small organic products are released into the soil

125
Q

What is the organic component of soil called ?

A

Humus

126
Q

What does humus allow the soil to do ?

A

The soil becomes able to support the growth of new species of plant, known as secondary colonisers

127
Q

How do secondary colonisers arrive ?

A

As spores and seeds

128
Q

What happens as the environmental conditions improve ?

A

New species of plant arrive

129
Q

What are these known as ?

A

Tertiary colonisers

130
Q

How do tertiary colonisers survive ?

A
  • These species can survive in conditions without an abundance of water
    • However, they need to obtain most of their water and mineral salts from the soil
131
Q

What happens at each stage of the intermediate community ?

A

The rock continues to be eroded and the mass of organic matter increases

132
Q

What happens when organisms decompose ?

A

They contribute to a deeper, more nutrient rich soil, which retains more water

133
Q

What does more nutrient rich soil allow for ?

A
  • More favourable abiotic conditions

- Initially for small flowering plants then shrubs then small trees

134
Q

Can the intermediate community have many seral stages ?

A
  • Yes

- Seral stages continue until climax conditions are obtained

135
Q

What happens at each different seral stage in the intermediate community ?

A
  • Different plant and animal species are better adapted to the current conditions in the ecosystem
    • They then outcompete many of the species that were previously present and become the dominant species
136
Q

What is the final seral stage ?

A

Climax community

137
Q

What are the features of a climax community ?

A
  • Stable state
  • Very few dominant plant and animal species
    • Which species make up the community depends on the climate
138
Q

How biodiverse is the climax community ?

A

It is not that biodiverse

139
Q

Why is the climax community not that biodiverse ?

A

Dominant species outcompeting pioneer and other species, resulting in their elimination

140
Q

When is biodiversity at its highest ?

A

Mid-succession

141
Q

What are primary consumers in animal succession ?

A
  • Insects and worms

- They are the first to colonise an area as they consume and shelter in the mosses present

142
Q

When do secondary consumers arrive ?

A

When a suitable food source has been established and the existing plant cover will provide them with suitable habitats

143
Q

When a suitable food source has been established and the existing plant cover will provide them with suitable habitats

A

The animals have to move in from neighbouring communities

144
Q

What is it called when succession is stopped artificially ?

A

Plagioclimax

145
Q

Who stops succession artificially ?

A

Humans

146
Q

What is one of the main reasons deflected succession occurs ?

A

Agriculture

147
Q

Give some examples of agriculture causing deflected succession

A
  • Grazing and trampling of vegetation by domesticated animals
  • Removing existing vegetation to plant crops
  • Burning as a means of forest clearance
148
Q

Why do scientists measure the distribution and abundance of organisms ?

A

This is a way of measuring and observing the biodiversity present within an ecosystem

149
Q

What does the distribution of organisms refer to ?

A

Where individual organisms are found within an organism

150
Q

What is the distribution of organisms like ?

A

Usually uneven throughout an ecosystem

151
Q

Where are organisms generally found ?

A
  • Where abiotic and biotic factors favour them
    • Therefore, their survival rate is high as all the resources they need to live are available to them and selection pressures are low
152
Q

How do you normally measure the distribution of organisms ?

A

A line or belt transect is normally involved

153
Q

What does a line transect involve ?

A

Laying a line or surveyor tape along the ground and taking samples at regular intervals

154
Q

What does a belt transect involve ?

A

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

155
Q

What types of sampling are transects ?

A

Systematic sampling

156
Q

What does the abundance of organisms refer to ?

A

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

157
Q

What does immigration and births cause ?

A

Increase the number of individuals

158
Q

What does emigration and deaths cause ?

A

Decrease the number of individuals

159
Q

What is a population ?

A

A group of similar organisms living in a given area at a given time

160
Q

Can populations be counted accurately ?

A

No

161
Q

Why cant populations be counted accurately ?

A
  • Some animals may elude capture
  • It may be too time consuming
  • Process could damage the environment
162
Q

How can you increase the accuracy of a sample ?

A
  • Use as large a sample size as possible

- The greater the number of individuals studied, the lower the probability that chance will influence the result

163
Q

How can you reduce the effect of sampling bias ?

A

Use random sampling

164
Q

How do you measure the abundance of plants ?

A
  • Use quadrats
    • The abundance of the organisms in that area is measured by counting the number of individual plants contained within the quadrat
165
Q

What is used to measure animal abundance ?

A

Capture-mark-release-capture technique

166
Q

What is the capture-mark-release-capture technique ?

A
  • Capture as many individuals as possible in a sample area
  • Mark or tag each individual
  • Release the marked animals back into the sample area and follow time for them to redistribute themselves throughout the habitat
  • Recapture as many individuals as possible in the original sample area
  • Record the number of marked and unmarked individuals present in the sample (release all individuals back into their habitat)
  • Use the Lincoln index to estimate the population size

Biology (30 decks)

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