Stability & Change

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교육자를 위해: Stability & Change(Biology, HL)을(를) 위한 바로 쓸 수 있는 수업 슬라이드, 복습 노트 — 수업에 사용하거나, 학습자들이 실시간 게임으로 즐기는 인터랙티브 클래스 활동으로 진행하세요.

수업 노트

Stability in Ecosystems

Stable ecosystems have efficient nutrient cycling, allowing them to be self-supporting.
They have high biodiversity, which contributes to stability.
They show resistance to change, e.g. consumer population sizes do not change significantly so resources are not overused.
They have high levels of photosynthesis, supported by light and moisture.
Tropical rainforests such as the Amazon and Congo have remained stable for tens of millions of years.
In rainforests, organic matter is cycled by detritivores (e.g. termites, slugs, worms) and decomposers (e.g. fungi), and water is cycled via transpiration and rainfall.
Ecosystems are not entirely static; natural selection and evolutionary change always act on species.

Requirements for Ecosystem Stability

A supply of energy is needed; for most ecosystems this is sunlight, converted to chemical energy by photosynthesis.
Recycling of nutrients is essential; without it, nutrient supply will run out.
Decomposers such as bacteria and fungi break down carbon compounds in dead organisms and waste, releasing carbon dioxide and minerals like nitrates and phosphates.
Conditions must be suitable for decomposers: enough oxygen and moisture, and suitable temperature.
If nutrients are removed (e.g. timber removal, crop harvest), cycling is interrupted and productivity is reduced.
Genetic diversity is the number of different alleles in a population; high diversity allows natural selection to act on favourable alleles for adaptation.
Climatic variables (e.g. temperature, rainfall) must remain within tolerance levels; extreme changes may force species to migrate or face extinction.
Human activities are causing climate change at a rate that pushes climatic variables beyond tolerance levels in some ecosystems.

Investigating Ecosystem Stability: Mesocosms

A mesocosm is an experimental container in which a naturally occurring ecosystem is simulated.
Mesocosms allow control of all factors other than the variable being studied.
They can be set up in many ways: water tanks for ponds/lakes, underwater enclosures for coastal waters, or greenhouse-like buildings for rainforests.
Mesocosm experiments can be considered unrealistic due to their enclosed nature and level of control; realism can be improved by making them larger.
In a lab mesocosm, the container should be transparent to allow sunlight to reach producers.
Autotrophs must be included so light energy is converted to chemical energy.
Small primary consumers (e.g. zooplankton) may be included, but secondary consumers should not be included due to insufficient energy and ethical concerns.
A control mesocosm must be set up identically but without changing the variable, to show any change is due to the altered factor.

Building Mesocosms

Terrestrial mesocosm: place drainage material (gravel), then charcoal to prevent mould, then sphagnum moss/filter paper, then soil/compost.
Plant slow-growing producers such as mosses and ferns; water before sealing with a lid.
Once stabilised, plants release enough water vapour during respiration to maintain moisture.
Aquatic mesocosm: base layer of organic substrate from a lake/pond provides nutrients and microorganisms.
Add lake/pond water (not tap water) to provide microscopic organisms; add healthy aquatic plants to produce carbohydrates and oxygenate water.
Only primary consumers should be used; do not add more organisms than the mesocosm can support.
IB guidelines require that investigations involving animals are not cruel and remove potential causes of distress; removing animals entirely is the most ethical approach.

Ecosystem Stability: Skills – Deforestation in the Amazon

Deforestation affects the self-sufficiency of the Amazon by influencing temperature and rainfall.
Transpiration releases water vapour, causing cooling and affecting air movement and rainfall.
Changes in tree number can influence local temperature and rainfall, which affect photosynthesis and nutrient cycling.
Scientists fear the Amazon could reach a tipping point beyond which it is no longer stable.
There is uncertainty about how much rainforest loss would trigger this tipping point.
Percentage loss of rainforest = (change in area / original area) × 100.

Keystone Species

Keystone species have a disproportionate effect on the structure and function of their ecosystem.
Their removal can cause significant changes, including loss of other species and possible ecosystem collapse.
Protecting keystone species helps maintain ecosystem stability, benefiting other species.
Sea otters control sea urchin populations; without them, urchins overgraze kelp vegetation.
Beavers build dams that slow water flow and create wetland habitats supporting many species.
Elephants in African grasslands consume shrubs and small trees, maintaining grassland for grazers and their predators.

A keystone species removed

Sustainability in Ecosystems & Agriculture

A sustainably harvested resource is replaced as rapidly as it is harvested, so it does not run out.
Sustainable use requires careful regulation and monitoring to prevent over-harvesting.
Black cherry (hardwood) is harvested sustainably by selective felling, leaving enough individuals to produce seeds, and regular monitoring.
The Alaska pollock fishery is the largest sustainably certified fishery, awarded by the Marine Stewardship Council (MSC).
Pollock are fast-growing, reproduce from age 3–4, nets have minimal seabed contact, and bycatch is <1%.
Agriculture sustainability is affected by soil erosion: clearing land removes roots, so topsoil is easily washed or blown away.
Leaching and nutrient run-off occur when rainfall washes soluble synthetic fertilisers into water bodies.
Other factors include fertiliser supply (expensive, energy-intensive) and pollution from agrochemicals (pesticides, herbicides, fungicides).
Carbon footprint of agriculture comes from fossil fuel use in transport, machinery, and fertiliser production.

Eutrophication

Eutrophication occurs when water bodies receive artificially large inputs of nutrients such as nitrates and phosphates.
Excess nutrients cause algal blooms, which block sunlight and kill aquatic plants below the surface.
Algae die when competition for nutrients becomes too intense.
Decomposing bacteria increase in number, respiring aerobically and using up dissolved oxygen.
This creates an increased biochemical oxygen demand (BOD).
Dissolved oxygen rapidly decreases, so fish and insects may not survive, creating dead zones.

An algal bloom

The Effects of Pollution

Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants with ascending trophic level.
It differs from bioaccumulation, which is the build-up of pollutants within an organism or single trophic level.
Pollutants become more concentrated at higher trophic levels because total biomass decreases up the food chain.
DDT is a persistent insecticide that biomagnified in birds of prey, causing thinning of eggshells and reduced reproductive success.
DDT is now banned worldwide except for essential use against malaria-transmitting mosquitoes.
Mercury from coal-fired power plants and gold mining is converted by microorganisms to methyl mercury, which accumulates in fish and can harm humans eating large predatory fish.
Plastics are non-biodegradable; macroplastics (>5 mm) and microplastics (<5 mm) harm wildlife through ingestion and entanglement.
Microplastics can release toxins that biomagnify in food chains.

Restoring Ecosystems

Human activities such as deforestation and overharvesting can destabilise ecosystems.
Ecosystem restoration (rewilding) aims to improve stability by restoring natural processes.
Strategies include species reintroductions (e.g. apex predators, keystone species).
Improving habitat connectivity via wildlife corridors (e.g. hedgerows) allows organisms to roam larger areas.
Limiting human influence may involve preventing logging, fishing, or agriculture, and using controlled grazing or burning.
Hinewai Reserve, New Zealand, was once farmland and is now restored by natural succession with minimal human intervention.
Gorse (×Ulex europaeus×) acted as a nursery species, helping native seedlings establish until they could outcompete it.

Ecological Succession

Ecological succession is the progressive change in species that make up a community over time.
It can be triggered by abiotic factors (e.g. volcanic activity, fire) or biotic factors (e.g. death and decomposition of organisms).
Primary succession occurs on newly formed or newly exposed land (e.g. volcanic rock, retreating glaciers).
Pioneer species (e.g. mosses, lichens) colonise bare land; they withstand harsh conditions and help form soil.
As soil deepens and becomes nutrient-rich, larger plants, shrubs, and trees can grow.
The final stable community is the climax community; its type depends on location (e.g. rainforest in tropics, deciduous woodland in temperate regions).
During succession: larger plant species are supported, primary production increases, species diversity increases, food webs become more complex, and nutrient cycling increases.
Secondary succession occurs on previously occupied land (e.g. after wildfire or deforestation); it is faster because soil is already present.
Cyclic succession is a repeating cycle of communities rather than a single climax, e.g. grazed wood pasture over hundreds of years.

Human Influence on Succession

Human activities often prevent or interrupt succession, stopping the climax community from developing.
The expected climax community depends on the biome (e.g. temperate forest in temperate climates).
Grazing by livestock prevents tree seedling establishment, so forest may not develop.
Drainage of wetlands prevents peat bog formation; wetlands may be drained for agriculture, development, or peat fuel.
In some cases, interrupting succession maintains important habitats such as heathlands, meadows, and chalk grasslands.

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1.Which of the following is the name given to an experimental container in which a naturally occurring ecosystem is simulated?
Easy
- AA mesocosm
- BA climax community
- CA keystone species
- DA biome
2.Which of the following statements about keystone species is correct?
Easy
- AKeystone species are always top predators.
- BKeystone species do not affect the diversity of their surrounding ecosystems.
- CThe influence of a keystone species on its ecosystem is equivalent to that of any other species.
- DRemoving a keystone species risks ecosystem collapse.
3.What is required for an ecosystem to be stable over an extended time period? I. An external supply of soil nutrients II. Genetic diversity III. An energy supply
Easy
- AI and II only
- BI and III only
- CII and III only
- DI, II and III
4.In a simple aquatic mesocosm, a healthy aquatic plant is an important component. Why is this?
Easy
- AIt provides protection for the primary consumers from predators.
- BIt converts heat energy to chemical energy.
- CIt provides carbohydrates and oxygen to support the mesocosm.
- DIt helps to maintain a stable temperature.
5.Which of the following are features of a stable ecosystem? (select all that apply)
Easy
- AEfficient nutrient cycling
- BHigh biodiversity
- CRapid and constant change in species composition
- DHigh levels of photosynthesis
- EDependence on external nutrient inputs
6.A region of rainforest with an area of 4 100 000 km² was reduced to an area of 3 855 000 km² over a ten year period. What is the percentage decrease in area?
Easy
- A4%
- B6%
- C8%
- D10%
7.Which of the following statements relating to deforestation in the Amazon rainforest is correct?
Easy
- AOnly a small area of rainforest is needed to sustain the cycle of transpiration and rainfall that maintains the ecosystem.
- BA region of rainforest with an area of 4 100 000 km² was reduced to an area of 3 855 000 km² over a ten year period, resulting in a percentage decrease of 6%.
- CScientists know the area of rainforest that needs to be maintained in order to avoid passing a tipping point in rainforest stability.
- DThe Amazon rainforest will remain stable regardless of how much deforestation occurs.
8.Keystone species are always top predators.
Easy
True or false?

더 많은 문제

9.In a mesocosm, it is possible to control all factors other than the variable being studied.
Easy
True or false?
10.A climax community is always the most biodiverse stage of succession.
Easy
True or false?
11.Which of the following best defines a keystone species?
Medium
- AA species that has a disproportionate effect on the structure and function of its ecosystem.
- BA species that is always the most abundant in its ecosystem.
- CA species that has no effect on other species in its ecosystem.
- DA species that is always found at the top of a food chain.
12.Which of the following is the correct definition of genetic diversity?
Medium
- AThe number of different species in an ecosystem.
- BThe number of different alleles of genes present in a population.
- CThe total number of individuals in a population.
- DThe variety of ecosystems in a biome.
13.Which of the following is the correct definition of biomagnification?
Medium
- AThe build-up of pollutants within a single organism.
- BThe increase in concentration of persistent or non-biodegradable pollutants with ascending trophic level through a food chain.
- CThe breakdown of pollutants by decomposers in an ecosystem.
- DThe movement of pollutants from water to land.
14.Which of the following is the correct definition of ecological succession?
Medium
- AA sudden change in an ecosystem caused by a natural disaster.
- BProgressive change in the species that make up an ecological community over time.
- CThe movement of individuals into and out of a population.
- DThe seasonal changes in weather patterns within an ecosystem.
15.In a grazed wood pasture, which sequence of events correctly describes part of the cyclical succession?
Medium
- ATrees grow, grazers prevent tree seedling growth, brambles create thorny scrub, trees die and create open areas.
- BGrazers consume tree seedlings in grassland, fast-growing thorny species such as brambles create scrub, tree seedlings survive within the thorny vegetation, trees grow through the scrub, trees die and create open areas where grass can grow.
- CGrass grows, trees die, brambles are removed by grazers, grass is replaced by woodland.
- DBrambles grow first, then grazers remove them, then trees grow and are never replaced.
16.Which of the following best describes the difference between primary and secondary succession?
Medium
- APrimary succession occurs on newly formed or newly exposed land, while secondary succession occurs on previously occupied land where soil is already present.
- BPrimary succession occurs after a wildfire, while secondary succession occurs on bare rock.
- CPrimary succession is faster than secondary succession because soil is already present.
- DPrimary succession involves only animals, while secondary succession involves only plants.
17.Secondary succession progresses more quickly than primary succession because soil is already present.
Easy
True or false?
18.A student sets up a mesocosm in a transparent container with a lid, containing soil, mosses, ferns, and water. Which of the following best explains why the container should be transparent?
Medium
- ATo allow sunlight to reach producers inside the mesocosm so that photosynthesis can occur.
- BTo prevent organisms from entering or leaving the mesocosm.
- CTo maintain a stable temperature inside the mesocosm.
- DTo allow oxygen to escape from the mesocosm.
19.Which of the following is the correct sequence of stages in primary succession on bare rock?
Medium
- ALichens and mosses → small plants and grasses → larger plants and shrubs → large trees → climax community
- BLarge trees → shrubs → grasses → lichens and mosses → climax community
- CSmall plants and grasses → lichens and mosses → large trees → shrubs → climax community
- DClimax community → pioneer species → small plants → large trees
20.Which of the following correctly describes the role of decomposers in nutrient cycling within a stable ecosystem?
Medium
- AThey convert light energy into chemical energy.
- BThey break down carbon compounds in dead organisms and waste, releasing carbon dioxide and minerals such as nitrates and phosphates.
- CThey consume primary producers and pass energy up the food chain.
- DThey prevent the growth of mould in a mesocosm.
21.Which of the following are features of a climax community? (select all that apply)
Hard
- AIt is a stable community.
- BIt contains all the different plant and animal species that have colonised the land.
- CIt is always the most biodiverse stage of succession.
- DIt is the final community formed at the end of succession.
- EIt is dominated by pioneer species such as lichens.
22.Which of the following factors affect the sustainability of agriculture? (select all that apply)
Hard
- ASoil erosion
- BLeaching and nutrient run-off
- CFertiliser supply
- DCarbon footprint
- EThe colour of the soil
23.Which of the following best explains why deforestation could cause the Amazon rainforest to reach a tipping point beyond which it is no longer stable?
Hard
- AFewer trees carry out transpiration, which can change local temperature and rainfall patterns, affecting photosynthesis and nutrient cycling.
- BDeforestation increases the rate of photosynthesis in the remaining trees.
- CDeforestation increases the supply of soil nutrients, making the ecosystem more stable.
- DDeforestation has no effect on temperature or rainfall patterns.
24.Biomagnification is the build-up of pollutants within a single organism or within a single trophic level.
Medium
True or false?
25.In a mesocosm, secondary consumers should not be included because there will not be enough energy in the food chain to sustain them for long.
Medium
True or false?
26.A student is building a terrestrial mesocosm in a clear container. They place gravel at the bottom, then a layer of charcoal, then a layer of sphagnum moss, then soil, and plant slow-growing mosses and ferns. What is the purpose of the charcoal layer?
Hard
- ATo provide nutrients for the plants.
- BTo help prevent the growth of mould.
- CTo hold the soil in place.
- DTo allow water to drain away.
27.Which of the following best explains why a control mesocosm is set up alongside an experimental mesocosm?
Hard
- ATo demonstrate that any change in the experimental mesocosm is due to the altered factor and not another factor.
- BTo provide extra organisms for the experimental mesocosm.
- CTo increase the rate of photosynthesis in the experimental mesocosm.
- DTo prevent the experimental mesocosm from overheating.
28.Match each term with its correct definition.
Medium
- Mesocosm
- Keystone species
- Biomagnification
- Climax community
- An experimental container in which a naturally occurring ecosystem is simulated
- A species that has a disproportionate effect on the structure and function of its ecosystem
- The increase in concentration of persistent pollutants with ascending trophic level
- The final, stable community formed at the end of succession
29.Place the stages of primary succession on bare rock in the correct order, from earliest to latest.
Medium
- Seeds and spores land on exposed rock and begin to grow
- Pioneer species such as mosses and lichens colonise the rock
- Dead organic matter forms soil
- Small plants and grasses grow in the shallow soil
- Larger plants, shrubs, and small trees grow
- Large trees become dominant, forming the climax community
30.The biologists hypothesised that the results shown in the graph were due to succession taking place on the island. Which of the following best explains why they think this?
Medium
- AThe percentage cover of pioneer species such as lichens decreased over time, while the percentage cover of larger plants such as grasses and trees increased.
- BThe percentage cover of all plant species remained constant over time.
- CThe percentage cover of large trees decreased over time while lichens increased.
- DThe island was colonised by large trees first, followed by mosses and lichens.
31.If the biologists just wanted to study the abundance of broad-leaved trees on the island, they could have used frequency rather than percentage cover. Why would this be possible?
Medium
- AFrequency is quicker to record and gives an indication of abundance when the species is large and easy to identify.
- BFrequency measures the exact area covered by each tree.
- CFrequency is only used for small, slow-growing species.
- DFrequency measures the number of individuals of a species rather than their distribution.
32.Why is A an important component of the mesocosm?
Easy
- AA provides protection for the primary consumers from predators.
- BA converts heat energy to chemical energy.
- CA provides carbohydrates and oxygen to support the mesocosm.
- DA helps to maintain a stable temperature.
33.Which of the following considerations should be taken into account when building a mesocosm to test the impact of a particular environmental variable? (select all that apply)
Medium
- AA transparent container should be used.
- BNo secondary consumers should be included.
- CAutotrophs should be included.
- DA control mesocosm should be built.
- ESoil should be sterilised to prevent contamination.
34.Match each term relating to ecosystem stability with its correct definition.
Medium
- Efficient nutrient cycling
- High biodiversity
- Resistance to change
- Genetic diversity
- Allows an ecosystem to be self-supporting
- A large number of different species present in an ecosystem
- Consumer population sizes do not change significantly so resources are not overused
- The number of different alleles of genes present in a population
35.Which of the following statements about the requirements for ecosystem stability are correct? (select all that apply)
Hard
- AA reliable source of energy, usually sunlight, must be present
- BNutrients must be recycled so the supply does not run out
- CAn external supply of soil nutrients is essential
- DConditions must be suitable for decomposers, with enough oxygen and moisture
- EClimatic variables may change beyond tolerance levels without affecting stability
36.Which of the following are correct considerations when building a mesocosm in the laboratory? (select all that apply)
Medium
- AThe container should be transparent so sunlight reaches producers
- BAutotrophs should be included to convert light energy into chemical energy
- CSecondary consumers should be included to maintain food chain length
- DA control mesocosm should be set up at the same time
- EProducers should be fast-growing to maximise oxygen production
37.Which of the following statements about keystone species are correct? (select all that apply)
Hard
- AThey have a disproportionate effect on the structure and function of their ecosystem
- BTheir removal can cause significant changes including loss of other species
- CThey are always top predators
- DProtecting them can help maintain ecosystem stability
- ETheir influence on the ecosystem is equivalent to that of any other species
38.Which of the following are consequences of eutrophication in a lake receiving fertiliser run-off? (select all that apply)
Hard
- AExcess growth of algae forming an algal bloom
- BIncreased light penetration to submerged aquatic plants
- CDeath of submerged aquatic plants due to lack of light for photosynthesis
- DIncreased biochemical oxygen demand (BOD) as decomposing bacteria respire
- EIncreased dissolved oxygen availability for fish and insects
39.Which of the following statements about biomagnification are correct? (select all that apply)
Hard
- AIt is the increase in concentration of persistent pollutants with ascending trophic level
- BIt is the same as bioaccumulation, which is the build-up of pollutants within a single organism
- CIt occurs because organisms at higher trophic levels consume many organisms from lower levels
- DIt only affects biodegradable pollutants
- EDDT is an example of a pollutant that undergoes biomagnification
40.Place the stages of cyclical succession in a grazed wood pasture in the correct order.
Medium
- Grazers consume tree seedlings in open grassland, preventing tree growth
- Fast-growing thorny species such as brambles create patches of scrub
- Tree seedlings survive within the thorny vegetation, which deters grazers
- Trees grow up through the scrub, which dies off due to lack of light
- The mature tree dies and falls, creating an open area where grass can grow again
41.What is the name given to the first species to colonise newly formed or newly exposed land during primary succession?
Easy
42.What is the name given to the final, stable community formed at the end of succession?
Easy
43.A region of rainforest with an area of 4 100 000 km² was reduced to an area of 3 855 000 km² over a ten year period. Calculate the percentage decrease in rainforest area. Give your answer to the nearest whole number.
Medium
44.A small island has a surface area of 100 m². Biologists place 25 quadrats, each 1 m², and find grass present in 15 of them. Calculate the mean percentage cover of grass on the island. Give your answer as a percentage.
Medium
45.Complete the sentence about the definition of a mesocosm.
Easy
A ____ is an experimental container in which a naturally occurring ecosystem is simulated.
46.Complete the sentence about the definition of genetic diversity.
Medium
Genetic diversity is defined as the number of different ____ of genes present in a population.
47.Complete the sentence about the definition of biomagnification.
Medium
Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants with ascending ____ level through a food chain.
48.Complete the sentence about the definition of ecological succession.
Medium
Ecological succession is progressive change in the ____ that make up an ecological community over time.
49.A region of rainforest with an area of 4 100 000 km² was reduced to an area of 3 855 000 km² over a ten year period. Calculate the percentage decrease in rainforest area.
Medium
50.A small island has a surface area of 100 m². Biologists place 25 quadrats, each 1 m², and find grass present in 15 of them. Calculate the mean percentage cover of grass on the island.
Medium
51.State two features of a climax community.
Hard
52.Identify three key features of a stable ecosystem.
Hard
53.Explain why succession in the Hinewai Reserve is likely to occur more quickly than in examples of primary succession.
Hard
54.The biologists are trying to decide if the grasses and broad-leaved trees that are currently present on the island represent the climax community. State two features of a climax community.
Hard
55.With reference to the island ecosystem, describe what may be observed if cyclical succession were to take place.
Hard
56.A region of rainforest with an area of 4 100 000 km² was reduced to an area of 3 855 000 km² over a ten year period. Calculate the percentage decrease in rainforest area. Give your answer to the nearest whole number.
Medium
- A8 %
- B6 %
- C7 %
- D5 %
57.A small island has a surface area of 100 m². Biologists place 25 quadrats, each 1 m², and find grass present in 15 of them. Calculate the mean percentage cover of grass on the island. Give your answer as a percentage.
Medium
- A72 %
- B66 %
- C60 %
- D54 %
58.A region of rainforest with an area of 4 100 000 km² was reduced to an area of 3 855 000 km² over a ten year period. Calculate the percentage decrease in rainforest area.
Medium
- A8 %
- B7 %
- C6 %
- D5 %
59.A small island has a surface area of 100 m². Biologists place 25 quadrats, each 1 m², and find grass present in 15 of them. Calculate the mean percentage cover of grass on the island.
Medium
- A54 %
- B60 %
- C66 %
- D72 %

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