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Biology > A2 CH5 population size and ecosystems > Flashcards

A2 CH5 population size and ecosystems Flashcards

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1
Q

What determines the size of a population at a particular time?

A

Birth rate, death rate, immigration, emmigration

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2
Q

What are fugitive species?

A

species that are poor at competition, they rely on reproduction and dispersal to increase their numbers

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3
Q

What are equilibrium species?

A

Species that control their population by competition within a stable habitat

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4
Q

What are equilibrium species growth pattern?

A

Their growth pattern is a sigmoid curve called the one step growth curve

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5
Q

What are the four phases in a one step growth curve?

A

Lag phase, exponential phase, stationary phase, death phase

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6
Q

What happens in the lag phase?

A

Initially, population doesn’t increase but then there is a period of slow growth.
It is a period of adaption or preparation for growth, with high metabolic activity (e.g. for enzyme synthesis)

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7
Q

What happens in the exponential phase?

A

Numbers increase logarithmically as there are no factors limiting growth.

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8
Q

Why can’t the exponential phase be maintained indefinitely?

A

Due to environmental resistance. Less food is available, concentration of waste products become toxic, not enough space. As well as biotic factors such as predation, parasitism, competition. And abiotic factors such as light intensity, soil pH, and temperature.

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9
Q

What happens in the stationary phase?

A

Birth and death rates are equal. Population has reached its carrying capacity. It is not constant, number of individuals fluctuates around the carrying capacity in response to environmental changes, it is regulated by negative feedback (often due to predator-prey relationships)

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10
Q

What happens in the death phase?

A

Factors that have reduced population growth before have become more significant. Population size decreases. Death rate is greater than birth rate.

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11
Q

What is a density-dependent factor?

A

Factors that have a large affect on denser populations. They are biotic factors which include disease, predation, and competition of food.

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12
Q

In a dense population, what can predators and parasites do?

A

Predators can find prey more easily. Parasites are transmitted more efficiently.

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13
Q

What are density-independent factors?

A

Abiotic factors that have the same affect regardless of the population size. Usually due to a sudden change in an abiotic factor such as a flood or fire.

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14
Q

How does a population fluctuate around the carrying capacity?

A

If the population rises above the set point, density-dependent factors increase and population declines. If the population falls below the set point, environmental resistance is temporarily relieved so the population rises again.

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15
Q

What is the abundance of a species?

A

the measure of how many individuals exist in a habitat

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16
Q

Why should sampling be random?

A

to eliminate sampling bias

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17
Q

What are the assumptions when using the mark release recapture technique?

A

that no births, deaths, immigration, emigration occurred during the time between collecting both samples

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18
Q

How does the mark release recapture technique work?

A
  1. Animals are captured, marked, then released (animals cannot be harmed or made more visible to predators)
  2. After animals have reintegrated with the population, traps are reset
  3. Use lincoln index calculation
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19
Q

How does kick sampling work?

A
  1. Kick or rake a set area for a set period and collect invertebrates in a net downstream
  2. Use simpons index to calculate diversity
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20
Q

What are quadrats and transects used for?

A

Used to estimate the percentage cover of plant species

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21
Q

What is an ecosystem?

A

A community in which energy and matter are transferred in complex interactions between the environment and organisms involving abiotic and biotic elements

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22
Q

What does a food chain show?

A

It represents the energy flow through an ecosystem

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23
Q

Decomposition involves what type of organisms?

A

Decomposed and detritivores

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24
Q

What are detritivores?

A

Detritivores (earthworm, woodlice) feed on detritus (remnants of dead organisms)

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25
Q

What are decomposers?

A

Decomposers (bacteria and fungi) feed via eternal digestion (saprotrophism). They obtain nutrients from dead organisms and waste products

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26
Q

What limits the length of a food chain?

A

Energy is lost at each level along the food chain. Less energy is incorporated into biomass and is available to the next trophic level. After 4 or 5 trophic levels, theres not enough energy to support another one.

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27
Q

What does the length of a food chain depend on?

A

The amount of energy that enters a food chain in the first trophic level (energy fixed in photosynthesis)

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28
Q

Why are tropical food chains longer than arctic food chains?

A

Tropical areas have high light intensity all year round, so more energy is fixed at photosynthesis and the first trophic level, meaning more energy is available to the other trophic levels.

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29
Q

Why does the majority of light falling on a plant don’t get absorbed by the pigments within the chloroplast?

A
  1. Light is the wrong wavelength
  2. Light is reflected by the leaf waxy cuticle surface
  3. The light is transmitted through the leaf without striking a chlorophyll molecule
  4. Light doesn’t hit photosystem I or II
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30
Q

What is the gross primary productivity?

A

It is the rate of production of chemical energy in organic molecules by photosynthesis in a given area in a given time

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31
Q

What are the units of gross primary productivity

A

KJm^-2y^-1

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32
Q

Why is a large proportion of gross production released?

A

it is released by respiration of the plant to fuel e.g protein synthesis

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33
Q

What does the net primary productivity represent?

A

The energy in the plants biomass, the food available to primary consumers

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34
Q

How do you calculate the net primary productivity?

A

Gross primary productivity - respiration

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35
Q

Why is the true value of primary productivity lower?

A

Some biomass is used to form inedible material such as bark or roots which is out of reach for primary consumers

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36
Q

What is primary productivity?

A

The rate at which energy is converted by producers into biomass

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37
Q

What is secondary productivity?

A

The rate at which consumers convert the chemical energy of their food into biomass

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38
Q

Why do primary consumers obtain less energy than secondary/tertiary consumers?

A

Primary consumers have a cellulose-rich diet so the undigested materials end up as waste. Secondary/tertiary consumers that are carnivores have a protein-rich diet which is more readily and easily digested, so they obtain more energy from their food.

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39
Q

What are the different ecological pyramids?

A
  • Pyramid of numbers
  • Pyramid of energy
  • Pyramid of biomass
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40
Q

Why are pyramid of numbers less accurate?

A
  • They don’t take into account the size of organisms
  • They don’t recognize the different between young and adult forms
  • Range of numbers may be large so its hard to draw to scale
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41
Q

Why can the pyramid of numbers be inverted?

A

Trophic level can be inverted if a level has more organisms than the previous level

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42
Q

What does the pyramid of energy show?

A

The energy transferred from one trophic level to the next per unit area or volume, per unit time

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43
Q

What are some key points about the pyramid of energy?

A
  • Most accurate way of representing feeding relationships
  • Bars decrease accordingly as when material passes up the food chain, energy is lost
  • Never inverted
  • Easy to compare the efficiency of energy transfer between trophic levels in different communities
44
Q

What is the pyramid of biomass less accurate?

A
  • Difficult to measure (e.g. plant roots must be included)
  • Do not show the amount of energy flowing through the ecosystem
  • Species with similar biomass may have different lifespans, so the direct comparison of total biomasses is misleading
45
Q

Why can the pyramid of biomass be inverted?

A

When organisms have a rapid life cycle so its numbers replenish quickly

46
Q

What is succession?

A

The change in structure and species composition of a community over time.

47
Q

What is a climax community?

A

a stable, self-perpetuation community that has reached equilibrium with its environment, and no further change occurs

48
Q

What is primary succession?

A

Sequence of changes following the introduction of species into an area that has not previously supported a community.

49
Q

What is a sere?

A

Sequence of communities with different species and structures

50
Q

What is a seral stage?

A
  • a stage in succession

- each stage changes the environment and makes it more suitable for other species

51
Q

What happens when a new species immigrate in succession?

A

It may outcompete those that are there already, and succession progresses.

52
Q

What is an example of a pioneer species?

A

Algae

53
Q

What do climax communities have?

A
  • Great species diversity
  • Complex food web
  • Dominated by long lived plants
54
Q

What is secondary succession?

A
  • The recolonization of a habitat previously occupied by a community
  • Soil is present
  • Disrupted from succession by an event such as a fire / flood / cultivation
55
Q

What are in equilibrium in a climax community?

A
  • Gross primary productivity and total respiration
  • Energy used from sunlight and released by decomposition
  • Uptake of nutrients from the soil and the return by decayed animal and plant remains
  • New growth and decomposition, so the quantity of humus is constant
56
Q

When happens when a xerosere progresses?

A
  • Soil thickness increases, so the availability of water, humus and minerals increases too
  • Biomass increases
  • Biodiversity increases
  • There is resistance to invasion by new species
  • More stability to disruption by environmental changes
57
Q

What is a disclimax?

A

When human interference affect succession and prevent the development of a climax community

58
Q

What is an example of disclimax?

A
  • Grazing by cattles maintains grassland and prevent shrubs and trees of a normal succession growing
  • Deforestation removes a community of large trees, and smaller ones are replanted
59
Q

What are the differences between primary and secondary succession?

A
  • In primary succession, the surface is bare
  • In secondary succession, soil is present
  • In PS, pioneer organisms are lichens and mosses
  • In SS, pioneer organisms are small weedy plants
  • In PS, it takes a long time to reach a climax community as soil must be created through physical and biotic interactions
  • In SS, it reaches a climax community quicker as soil is already there
60
Q

What are factors that affect succession?

A
  • Migration
  • Competition
  • Facilitation
61
Q

How does migration affect succession?

A

Immigration of spores and seeds into an area is important in thee recolonization of an area. AS new species are introduced, competition exists for resources at all seral stages.

62
Q

What types of competition affect succession?

A

Intraspecific competition and interspecific competition

63
Q

What is intraspecific competition?

A
  • The competition between individuals of the same species
  • This type of competition is density-dependent
  • When a population is dense, more individuals fail to survive
  • Organisms produce more offspring than the habitat can support
  • Organisms with alleles that make them best suited to the environment reproduce more successfully
64
Q

what is interspecific compeition?

A
  • It is the competitions between individuals of different species
  • Each species have their own niche
65
Q

What is a niche?

A

An organisms role and position it has in the environment

66
Q

What are the two types of facilitation?

A

Mutualism and commensalism

67
Q

What is mutualism and commensalism?

A
  • Mutualism is the interaction between species that is beneficial to both
  • Commensalism is the interaction between organisms of 2 species where on benefits but the other is unaffected
68
Q

What type of human activities increase CO2 levels?

A
  • Burning fossil fuels

- Deforestation as it removes photosynthesizing biomass so less CO2 is beinng removed from the atmosphere

69
Q

What are the 3 biological processes in the carbon cycle?

A
  • Respiration (by animals, plants and micro-organisms with adds CO2 into the air
  • Photosynthesis which removes CO2 from the atmosphere
  • Decomposition which releases CO2 back in the air by detritivores and saprobionts
70
Q

What is the form of CO2 in aquatic ecosystems?

A

HCO3-

71
Q

What is the difference between the carbon cycle on land and in aquatic ecosystems?

A
  • CO2 in the air dissolves in the aquatic ecosystems as HCO3- (hydrogen carbonate ions)
  • Carbonates from exoskeletons (from the death of animals) become components of chalk, limestone and marble and when they are exposed to the atmosphere, erosion occurs, releasing CO2 back into the air
72
Q

How does deforestation impact the carbon cycle?

A

When trees are cut down, they are either burned or left there to decay, both releasing CO2

73
Q

What contributes to climate change?

A
  • Burning fossil fuels

- Deforestation

74
Q

What are the consequences of climate change?

A
  • Plants and animals may not be able to adapt or migrate and many will become extinct
  • Crop yield will be reduced
75
Q

What are the consequences of global warming?

A
  • Melting of polar ice resulting in costal areas flooding
  • Increased frequency of extreme weather conditions
  • More forest fires
  • Desertification as the availability of water has decreased
  • Evolutionary adaption is slow as the climate changes which leads to extinction
  • Higher temperatures will increase crop yield and pest population will increase
  • World food productions decrease
  • Acidification of ocean due to increasing dissolved CO2
76
Q

How does global warming lead to plants and animals becoming extinct, and the collapsing of an ecosystem?

A
  • Plants can only move as fast as they are dispersed, if its not fast enough they will become extinct
  • Animals dependent on plants will become extinct and the ecosystem may collapse
77
Q

How does ocean acidification affect aquatic organisms?

A
  • Fish gills produce mucus in response to increasing acidity, which reduces gas exchange
  • Coral reefs have external skeleton made of calcium carbonate which is soluble in acid
78
Q

What farming practices are used to reduce gas emissions?

A
  • Cover cropping
  • Crop rotation
  • Reducing dietary intake of meat and dairy products
  • Improve drainage to remove water and aerate the soil
79
Q

What farming practice is used when there is a low water supply?

A

Use drought tolerant crops

80
Q

What farming practice is used when the sea level is raised?

A

Use salt-tolerant crops

81
Q

What could be done to reduct the production of greenhouse gasses?

A
  • Plant trees in deforested areas
  • Drive less
  • Avoid food waste
82
Q

What is the nitrogen cycle?

A

The flow of nitrogen atoms between organic and inorganic nitrogen compounds and atmospheric nitrogen gas in an ecosystem

83
Q

Why is the nitrogen cycle important to support life?

A
  • Living organisms need nitrogen to make amino acids, proteins and nucleic acids
  • Plants and animals are unable to use nitrogen gas
  • Plants must absorb nitrates into their root nodules
  • Organic nitrogen compounds produced by plants are transferred through the food chain
  • Decomposition of plants and animals after death release minerals back into the soil
  • Excreted and egested products of animals release minerals back into the soil
84
Q

What are the four main biological processes in the nitrogen cycle?

A
  • Ammonification
  • Nitrification
  • Denitrification
  • Nitrogen fixation
85
Q

What is ammonification?

A
  • Decomposers such as bacteria and fungi secrete enzymes that decay dead organisms and animal products
86
Q

Explain the role of the enzymes that decomposers secrete in ammonification

A
  • Decomposers secrete protease and deaminase
  • Proteases digests proteins into amino acids
  • Deaminases remove NH2 groups from the amino acids and reduce them to ammonium ions
87
Q

What is nitrification?

A

The conversion of ammonium ions formed in ammonification into nitrites and nitrates

88
Q

What bacterias and reactions are involved during nitrification?

A
  • Nitrosomonas converts ammonium ions into nitries (oxidation reaction)
  • Nitrobacter converts nitrites into nitrates (oxidation reaction)
  • Both reactions oxidations
89
Q

What conditions do the bacteria in nitrification require?

A
  • Nitrosomonas and nitrobacter require aerobic conditions
90
Q

What is denitrification?

A

The loss of nitrate from the soil

91
Q

What bacteria is involved in denitrification and what conditions does it require?

A
  • Pseudomonas is an anaerobic bacteria that converts nitrate ions to nitrogen
  • The reactions is a reduction as oxygen is lost
  • Requires anaerobic soil
92
Q

Why is nitrogen fixation important?

A

Organisms can’t use atmospheric nitrogen as they don’t have the enzymes to break the triple bond between nitrogen atoms

93
Q

What is nitrogen fixation?

A

The reduction of nitrogen atoms in nitrogen molecules to ammonium ions by prokaryotic organisms

94
Q

What bacteria is involved in nitrogen fixation and what does it do?

A
  • Azotobacter is a free living nitrogen fixing bacteria in the soil
  • Rhizobium is a symbiotic nitrogen fixing bacteria found in the root nodules of plants such as legumes
95
Q

Name a plant where Rhizobium is found in the root nodules

A

Legumes

96
Q

What is the process of nitrogen fixation?

A
  1. Nitrogen gas diffuses into legume root nodules and nitrogenase catalyses its reduction to ammonium ions, using energy from ATP
  2. Ammonium ions are converted into organic acids and then to amino acids which are incorporated into bacterial proteins
97
Q

How do root nodules prevent oxidation reactions?

A
  • Nitrogen fixation required reduction reactions and is poisoned by oxidising conditions
  • Root nodules contain leg-haemoglobin that binds molecular oxygen inn nodules and protects reactions from oxidation (it makes the nodules pink)
98
Q

What practices do humans do to improve circulation of nitrogen in the soil?

A
  • Ploughing fields
  • Draining land
  • Artificial nitrogen fixation (harber process converts nitrogen to fertilisers)
  • Using brown manure
  • Using slurry
  • Using treated sewage sludge
  • Planting filed of legumes (alfafa or clover)
99
Q

How does ploughing fields improve the circulation of nitrogen in the soil?

A
  • Ploughing fields improve soil aeration
  • It favors:
  • Aerobic organisms such as free living nitrogen fixers, so it enhances the formation of ammonium ions in the soil
  • Nitrifying bacteria so it enhances the conversion of ammonium ions into nitrites and nitrates
  • Plant roots respire aerobically and generate ATP, so it fuels the active uptake of minerals
100
Q

How does draining land improve the circulation of nitrogen in the soil?

A
  • Draining land allows air to enter the soil

- It reduces anaerobic conditions which favor denitrifying bacteria, so loss of nitrates is reduced

101
Q

What is brown manure and how does it improve the circulation of nitrogen in the soil?

A
  • Animal waste is used as brown manure and it contains nitrogen and other nutrients essential for plant growth
  • Brown manure is spread on the surface
  • It improves the soil structure so it holds more nutrients and water
102
Q

What is slurry and how is it used?

A
  • Slurry is a liquid made from manure and water

- It is injected into the soil

103
Q

What is treated sewage sludge?

A

It is a sustainable alternative to inorganic fertilizers

104
Q

How does planting fields of legumes/alfafas/clovers improve the circulation of nitrogen in the soil?

A

It enhances nitrogen fixation

105
Q

How does eutrophication occur?

A
  1. Surface runoff or undersoil leaching causes nitrates to enter a body of water
  2. Increased availability of nitrates in the water leads to an increased reproductive rate of algae
  3. The algal bloom blocks light to plants in the water, preventing photosynthesis so the O2 concentration decreases
  4. The algae use up all the resources and enter the death phase
  5. Saprotrophic decomposers break down the dead algae, so the O2 concentration decreases further
  6. Eventually, the water becomes anoxic and plants and animals die, leaving anaerobic bacteria
106
Q

How do we avoid eutrophication?

A
  • Restrict the amount of fertilizer applied to the soil
  • Only apply fertilizers when crops are actively growing, so it is readily used and doesn’t remain in the soil to be leached away
  • Make sure fertilizers applied are at least 10m away from a body of water
  • Dig drainage ditches so minerals end up there and not natural bodies of water

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