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BIOLOGY A LEVEL > CHAPTER 23 - ECOSYSTEMS > Flashcards

CHAPTER 23 - ECOSYSTEMS Flashcards

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1
Q

What is Ecology

A

The study of relationships between organisms and their environment

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2
Q

What is an ecosystem made up of

A

All living organisms that interact with one another in a defined area

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3
Q

What are the two types of factors that affect ecosystems

A

Biotic and Abiotic

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4
Q

What are biotic factora

A

Living factors

eg. Forest ecosystem, shrews and hedgehogs are biotic factors as is the size of their populations - the competition between these two animal populations for a foot source

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5
Q

What is an abiotic factor

A

The non-living or physical factors. eg. The amount of rainfall received and the average temperatrue

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6
Q

Name some biotic factors

A

Most forms of competition eg. Competition for food, territory and breeding partners

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7
Q

What are some abiotic factors

A

Light
Temperature
Water availability
Oxygen availability
Edaphic (soil) factors

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8
Q

How is light an abiotic factor

A

Most plants are directly affected by light availability, as light is required for photosynthesis; greater light availability, the greater the success of the plant

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9
Q

What strategies do plants use to cope with different light intensities

A

Areas of low light will have larger leaves, develop photosynthetic pigments which require less light, or reproductive systems that only act when light availability is at an optiumum

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10
Q

How does temperature act as an abiotic factor

A

Affects rate of enzymes controlling metabolic reactions. Plants will develop more rapidly in warmer temperatures, and so will ectothermic animals

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11
Q

How do changes in temperature affect an ecosystem?

A

Trigger migration in some species
Triggers hibernation in others
Triggers leaf fall, dormancy or flowering in others

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12
Q

How does water availability act as an abiotic factor

A

Lack of water leads to water stress, which will lead to death

Causes plants to wilt as turgor pressure decreases and plant cannot stay upright or conduct photosynthesis

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13
Q

What are plants called that have adapted to deal with low water availability

A

Xerophytes eg. cacti

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14
Q

How does oxygen availability act as an abiotic factor

A

In aquatic ecosystems, it helps to have fast-flowing cold water which contains high concs of O2

If water becomes too warm, or flow rate too slow, the Oxygen conc will drop, leading to the suffocation of aquatic organisms

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15
Q

How does waterlogged soil affect plants

A

Air spaces are filled with water, reducing oxygen availability for plants

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16
Q

What are the types of soil size and how does it effect organisms

A

Clay - fine particles, easily waterlogged, and forms clumps when wet
Loam - This has different-sized particles, retains water but doesnt become waterlogged
Sandy - This has coarse, well-separated particles that allow free draining - sandy soil doesnt retain water and is easily eroded

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17
Q

Explain what is meant by the term ‘dynamic ecosystem’
To which ecosystem does the term apply

A

Ecosystem whose biotic and/or abiotic factor(s) are constantly changing

all ecosystems are dynamic

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18
Q

State two biotic and two abiotic factors in a pond

A

Biotic populations of (named) organisms

competition between (named organisms) for a
resource

Abiotic any two from (for example): temperature, light intensity, dissolved oxygen
concentration, pH

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19
Q

Explain why abiotic factors often have a greater effect on plant species than on animal species in an ecosystem

A

Animals able to migrate, e.g., towards warmer/cooler temperatures, to search for alternative food
supplies

animals able to move, e.g., to find shelter, to search out water supplies

many animals able to regulate their internal temperature, so less affected by temperature changes

many animals able to survive using a range of food sources

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20
Q

What is a trophic level?

A

A hierarchical level in an ecosystem, consisting of organisms sharing the same function in the food chain and the same nutritional relationship to the primary sources of energy

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21
Q

What is always the first trophic level

A

The producers

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22
Q

What is a producer

A

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

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23
Q

What are the subsequent trophic levels after produces

A

Consumers

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24
Q

What are consumers

A

Organisms that obtain their energy by feeding on other organisms

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25
Q

What are primary consumers

A

The consumer that easts a producer

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26
Q

How are consumers the labelled

A

Successively,
Secondary consumers consume primary consumers
Tertiary consumers consume secondary consumers etc…

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27
Q

What do decomposers do

A

Break down dead organisms, releasing nutrients back into the ecosystem

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28
Q

How is biomass represented

A

Biomass pyramids
(pg 611)

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29
Q

What is biomass

A

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

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30
Q

How do you calculate the biomass at each trophic level

A

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

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31
Q

What is the flaw in calculating biomass

A

only calculates biomass present at a particular time, and doesn’t take into account seasonal changes

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32
Q

What is the easiest way to measure biomass

A

Measure fresh material, discounting the water, so a dry mass is needed

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33
Q

How are organisms prepared to calculate dry mass

A

Killed, Placed in an oven at 80 degrees celsius until all the water has evaporated - when a constant mass is achieved

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34
Q

What units are biomass measured in?

A

Joules or Grams per metres squared of land, or cubed in water

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35
Q

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

A

When animals eat, only a small proportion of the food they ingest is converted to new tissue

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36
Q

How is the energy available at each trophic level calculated

A

kilokoules per metre squared per year

kJ m-2 yr-1

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37
Q

What is ecological efficiency

A

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

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38
Q

What percentage of sunlight do producers convert into chemical energy and therefore biomass

A

1-3%

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39
Q

Why do producers only convert a small percentage of sunlight into biomass

A

Not all the solar energy available is used for photosynthesis - approximately 90% is reflected

Other factors may limit photosynthesis eg. water availability

A proportion of the energy is lost - as it is used for photosynthetic reactions

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40
Q

How can energy available at the next trophic level be calculated

A

Net production = gross production - respiratory losses

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41
Q

Why do consumers at each tropic level convert at most 10% of the biomass in their food to their own organic tissue?

A

Not all the biomass of an organism is eaten, eg. Bones and roots not eaten

Some energy is transferred to the environment as metabolic heat

Some parts of an organism are eaten but indigestible and egested as faeces

Some energy is lost from the animal in excretory processes

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42
Q

How do you calculate ecological efficiency

A

(Energy or biomass available after transfer/ energy or biomass available before transfer) x100

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43
Q

What impact can humans have on biomass in an ecosystem

A

Agriculture

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44
Q

How many trophic levels are in a livestock agriculture

A

Producer - Animal Feed
Primary consumers - livestock eg. Cow
Secondary consumer - Human

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45
Q

Describe how the biomass of a trophic level is measured

A

Wate removed from one organism by heating it in an oven at 80°C

the ‘dry’ organism is then

weighed to measure its mass in grams

this figure is multiplied by number of organisms present in
given area

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46
Q

Explain how human activities can manipulate the transfer of biomass through ecosystems

A

Through agriculture number of trophic levels in food chain is minimised

to maximise energy /
biomass transfer to humans

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47
Q

Explain why biomass decreases at each level in a food chain

A

Energy is lost from an organism because (any three from): not all of an organism may be eaten,

parts of an organism may be indigestible,
some energy is transferred to the environment through
metabolic heat, some energy is lost through excretion

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48
Q

How does energy flow through an ecosystem

A

Linearly

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49
Q

What is decomposition

A

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

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50
Q

How are unusable forms of essential elements such as nitrogen or carbon, processed into being used

A

Turned into inorganic elements and compounds and returned to environment

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51
Q

What is a decomposer

A

An organism that feeds and breaks down dead plant or animal matter, thus turning organic compounds into inorganic ones (nutrients) available to photosynthetic producers

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52
Q

How big are decomposers

A

Primarily microscopic such as fungi and bacteria, but also include larger fungi such as toadstools and bracket fungi

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53
Q

Why are decomposers saprotrophs

A

Because the obtain their energy from dead or waste or organic material (saprobiotic nutrition)

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54
Q

How do decomposers eg. fungi digest their food

A

Secrete enzymes externally onto dead organisms or waste matter

Enzymes break down complex molecules into simpler soluble molecules - which are absorbed by decomposers which are then released into the environment

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55
Q

What are Detritivores

A

Another class of organism involved in decomposition

56
Q

How do detritivores help speed up the decay process?

A

feeding on detritus - dead and decaying material

This breaks it down into smaller pieces of organic material, increasing Surface Area for the decomposers to work on

57
Q

What are some examples of detritivores

A

Woodlice - break down wood
Earthworms - Break down dead leaves

58
Q

How do detritivores digest matter

A

Performs internal digestion

59
Q

How do animals obtain the nitrogen they need

A

Through food eaten

60
Q

How do plants obtain the nitrogen they need

A

Take it from the environment

61
Q

What is Nitrogen an essential element for?

A

making amino acids (consequently proteins) and amino acids

62
Q

What percentage of the atmosphere is Nitrogen gas (N2)

A

78%

63
Q

To be used by living organisms, what does nitrogen need to be combined with

A

Oxygen or Hydrogen

64
Q

What organisms play a vital role in converting nitrogen into a useable form for plants

A

Bacteria
(without bacteria, Nitrogen would become a limiting factor in ecosystems)

65
Q

What are the two nitrogen-fixing bacteria called?

A

Azobacter and Rhizobium

66
Q

What do nitrogen-fixing bacteria contain to carry out the Haber process

A

The Enzyme Nitrogenase, which catalyses the combination of atmospheric nitrogen with Hydrogen to produce Ammonia, which can be absorbed by plants

67
Q

What is Nitrogen fixation

A

the fixing of nitrogen to hydrogen to form ammonia, which can be absorbed by plants (hater process)

68
Q

Where does the Azobacter bacterium live and what does it do

A

Lives in soil
Nitrogen Fixation

69
Q

Where does the Rhizobium bacterium live and what does it do

A

Lives in Root nodules
nitrogen fixation

70
Q

What are Root nodules

A

Growths on the roots of leguminous plants such as peas beans and clover

71
Q

What relationship do Rhizobium and plant have and why

A

Symbiotic/ mutualistic

Plant gains amino acids from bacteria when the fix nitrogen into ammonia

Bacteria gains carbohydrates produced by the plant during photosynthesis which is used as an energy source

72
Q

How do plants maximise their benefit with colonies of Rhizobium

A

Reward and Punishment

Beneficial colonies receive extra carbohydrates

Less-productive bacteria’s supply of carbohydrates is cut off and that starves the nodule to death

(Natural selection)

73
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

74
Q

What type of reaction is nitrification and what type of soil can it only occur in

A

Oxidation reaction

Well-aerated soil

75
Q

What are the two steps in Nitrification

A

Nitrifying bacteria (eg. Nitrosomonas) oxidise ammonium into nitrites (NO2-)

Nitrobacter oxidises nitrites into Nitrates (NO3-)

76
Q

What is the formula for a Nitrite

A

NO2 -

77
Q

What is the formula for a Nitrate

A

NO3 -

78
Q

What property of Nitrate ions means that they enter plants easily

A

Soluble

79
Q

What is Denitrification

A

In the absence of oxygen, Denitrifying bacteria convert nitrates in the soil back to nitrogen gas

80
Q

What are the conditions in which denitrification takes place

A

An oxygen deficient (anaerobic) environment eg. Waterlogged soils

81
Q

What do the Bacteria use the Nitrates for in denitrification

A

Source of energy for respiration, releasing N2(g)

82
Q

What is ammonification

A

The process by which decomposers convert nitrogen-containing molecules in dead organisms, faeces and urine into ammonium compounds

83
Q

What are the two types of bacteria involved in Nitrification

A

Nitrosomonas (NH3 -> NO2 -)
Nitrobacter (NO2 - -> NO3 -)

84
Q

CARBON CYCLE

A

PAGE 619

85
Q

Why do CO2 levels fluctuatee throughout the day?

A

Photosynthesis only takes place during the light - removing carbon dioxide form the atmosphere

Respiration happens constantly, releasing set volume of CO2

Therefore CO2 levels are higher during the night than in the day

86
Q

How can carbon fluctuate during the seasons

A

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

87
Q

Why have global atmospheric carbon dioxide levels increased significantly over the last 200 years

A

Combustion of fossil fuels, which has released CO2 back into the atmosphere from carbon that had been trapped below the earths surface for millions of years

Deforestation - removed lots of photosynthesising biomass from earth, so less CO2 is removed. Some forests are cleared by burning, releasing more CO2

88
Q

Why is CO2 a greenhouse gas

A

Increased levels of CO2 traps more thermal energy (heat) in the atmosphere

89
Q

How does the amount of CO2 dissolved in the seas and oceans affect temperature

A

Higher temperature - less gas is dissolved, more is released into atmosphere, contributing to global warming

positive feedback loop

90
Q

How can carbon dioxide level variation be measured over million-year scales

A

Sample taken deep within a glacier eg. Antarctic glaciers

Air bubbles trapped in ice reflect composition of atmosphere at that point of time

Analysed to reveal composition of atmosphere

91
Q

State the main differences between a decomposer and a detritivore

A

Detritivores break down organic matter into small pieces, providing a larger surface area for decomposers to act on

detritivores carry out internal digestion whereas decomposers carry out external digestion

92
Q

State and explain there ways in which atmospheric CO2 levels increase

A

Respiration carbon dioxide is released as a waste product of respiration and from the bodies of dead organisms through respiration of decomposers

Combustion burning of forests/fossil fuels releasing carbon dioxide as a waste product

Deforestation fewer trees and plants mean less carbon dioxide is removed from the atmosphere

93
Q

Describe what is meant by saprobiotic nutrition

A

When a decomposer obtains its energy from dead organisms

by the process of external digestion/process

94
Q

Explain how the scientific community have produced evidence that atmospheric carbon dioxide levels have varied over time

A

Ice core samples are collected from glaciers which have existed for many (tens/hundreds of) thousands of years

air bubbles trapped within these glaciers are representative of the atmosphere at a point in history

gas analysis of trapped air bubbles reveals atmospheric composition at this point in history

95
Q

What is Succession

A

The process by which ecosystems change over time

96
Q

Why does succession occur

A

Due to changes to the environment causing plant and animal species to change

97
Q

What is primary succession

A

Occurs on an area of land that has been newly formed or exposed such as bare rock.

There is no soil or organic material present to begin with

98
Q

What is secondary succession

A

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

Eg. Bare earth that remains after a forest fire

99
Q

When does primary succession occur

A

When volcanoes erupt, depositing lava, lava cools and solidifies creating igneous rock

Sand is blown away by wind or deposited by the sea to create new sand dunes

Silt and mud are deposited at river estuaries

Glaciers retreat depositing rubble and exposing rock

100
Q

What is a serial stage (or a sere)

A

A step of succession

101
Q

What can be found at each seral stage which change abiotic factors such as the soil to make it more suitable for the subsequent existence of other species

A

A key species

102
Q

What are the main seral stages

A

Pioneer community
Intermediate community
Climax community

(pg 621)

103
Q

What is a pioneer species

A

The first species to colonise an inhospitable environment

104
Q

How do pioneer species arrive at the inhospitable environment

A

As spores or seeds carried by the wind from nearby land masses

or Droppings of birds or animals passing through

105
Q

What is an example of a pioneer species

A

Algae or Lichen

106
Q

What are some adaptions pioneer species have to enable them to colonise the bare environment

A

Ability to produce large quantities of seeds or spores, which are blown by the wind and deposited on the ‘new land’

Seeds that germinate rapidly

Ability to photosynthesise (only factors would be light, rainfall and air)

Tolerance to extreme conditions

Ability to fix nitrogen from the atmosphere, so adding to the mineral content of the soil

107
Q

What is humus

A

The organic component of the soil when organisms of the pioneer species die and decompose

108
Q

How is an intermediate community formed

A

Weathering of the bare rock produces particles that form the basis of the soil, which alone cannot support other species]

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

Soil becomes able to support the growth of a new species of plant - secondary colonisers - supported by nitrates in soil and their ability to retain water

Arrive as spores or seeds eg. moss, provides source of food for animals

109
Q

What is an example of a secondary coloniser

A

Moss

110
Q

What are tertiary colonisers

A

Species that will arrives the environmental conditions continue to improve

111
Q

What is an example of a tertiary coloniser

A

Fern

112
Q

What are some adaptions of tertiary colonisers

A

Thick waxy cuticle to reduce water loss
HOWEVER
Gains water and mineral salts from soil

113
Q

What happens at each stage of the intermediate community seral stages

A

Rock continues to be eroded

Mass of organic matter increases

Organisms decomposing contribute to a deeper, more nutrient-rich soil, retains more water

Allows for flowering plants such as grasses, shrubs and finally trees to grow

Plant and animal species are better adapted to the ecosystem, often outcompeting the species that were previously present

114
Q

What is the final seral stage called

A

Climax Community

115
Q

What are features of a climax community

A

Stable state - little change over time

A few dominant plant and animal species

A decrease in biodiversity from mid-succession due to dominant species outcompeting pioneer and other species

116
Q

What are primary consumers in animal succession and why

A

Insects and worms, first to colonise an area as they consume and shelter in the mosses and lichen

117
Q

Analogy for succession

A

Domino falling

Momentum needed for one to fall but eventually they all follow

118
Q

What is plagioclimax

A

When succession is stopped artificially, by human activities

119
Q

What are the some examples of deflected succession

A

Grazing and trampling of vegetation by domesticated animals

Removing existing vegetation to plant crops (crop becomes final community)

Burning as a means of forest clearance (can lead to an increase in biodiversity as it provides space and nutrient rich ash for other species to grow)
ALL AGRICULTURE

120
Q

READ SUCCESSION ON A SAND DUNE - 624

A
121
Q

State the difference between a climax community and a plagioclimax community

A

Climax community is the final stage of succession whereas plagioclimax community is the final stage of succession as deflected by humans or some other outside factor

122
Q

Describe the difference between primary and secondary succession

A

Primary succession occurs on bare rock/sand without soil

whereas secondary succession takes place where soil is present but the area contains no plants or animals

123
Q

State and explain the common developments that occur in succession in any ecosystem?

A

Abiotic conditions/non-living environment becomes less hostile as soil forms when organisms decay/ soil becomes more nutrient-rich/ soil retains more water

increased biomass supported

124
Q

What is the distribution of organisms

A

Refers to where individual organisms are found within an ecosystem

125
Q

What factors affect distribution of organisms

A

Organisms are found where abiotic and biotic factors favour them, so their survival rates are high and there are plentiful resources and low predation

126
Q

How can distribution be measured

A

Belt transect

127
Q

What is the abundance of organisms

A

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

128
Q

How would you estimate plant abundance

A

usually use a quadrat
Random sampling

Number of individuals/area of sample

can be scaled up

129
Q

What method is used to measure animal abundance

A

Capture-mark-release-recapture

Est. population size = individuals in 1st sample x individuals in 2nd / Number of recaptured, marked individuals

130
Q

What are some equipment that is used to measure animal abundance

A

Pooter, sweep net, dip net, pitfall trap, Longworth mammal trap etc…

131
Q

What is Simpsons diversity index

A

D = 1-Sum of (n/N)2

D = Diversity indez
N = Total number of organisms in ecosystem
n= number of individuals in a species

Always a value between 0-1

132
Q

State the difference between the abundance and distribution of organisms

A

Abundance is the total number of organisms whereas distribution refers to where individuals are found

133
Q

Twenty woodlice captured area and marked and released back into the same sample area. A week later 15 woodlice were found in the sample area of which only two were marked.
A) suggest which piece of apparatus should be used to collect the woodlice
B) Use the Lincoln Index to estimate the woodlouse population

A

A) Pooter/pitfall trap
B) 20 × 15 / 2 = 150

134
Q

What is the Lincoln index

A

Number marked in second sample / Total caught in second sample = Number marked in first sample / Size of whole population (N)

135
Q

State and explain one advantage of the following technique is used to measure the distribution of organisms in an ecosystem
A) random sampling
B) non-random sampling

A

A) Removes sample bias / makes sample more reliable

B) Allows scientist to study how differing abiotic factors may affect the distribution of a species

136
Q

Discuss the limitations of using the capture-mark-release-recapture technique to estimate population size

A

Doesn’t take into account births/deaths

immigration / emigration

mark may rub off

mark may make animals more visible to predators

animals don’t redistribute evenly

samples taken may not be representative of the whole population

137
Q

PRACTICE SIMPSONS DIVERSITY INDEX

A

BIOLOGY A LEVEL (24 decks)

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