SL Paper 3
Freshwater invertebrates were sampled by students at three sites along a river in central France. The animals were identified and counted. The diversity of each site can be compared using Simpson’s reciprocal index.
Simpson’s reciprocal index is given by the following formula:
Calculate the diversity of site C. Working should be shown.
Site A has a higher Simpson’s reciprocal index than Site B showing that its diversity is higher.
Explain the reason that ecologists consider Site A to have a higher diversity than Site B, despite both sites having six different species present.
Discuss the advantages and disadvantages of in situ conservation methods.
Markscheme
a. 
b. = 3.56 «allow 3.55»
a. the species in Site A are more evenly represented than site B
b. site B has a large number of one species «but very few in the other 5»
c. Simpson’s reciprocal index is a measure of species evenness as well as species richness
Advantages:
a. conservation in the natural habitat / ecosystem
b. the species will have all the resources that it is adapted to
c. the species will continue to evolve in their environment / can maintain genetic diversity
d. the species have more space so a bigger breeding populations can be kept
e. it is cheaper to keep an organism in its natural habitat
f. established food webs/ species interactions can be maintained
Disadvantages:
g. it is difficult to control illegal exploitation «eg poaching»/harder to monitor populations
h. the area may need restoring / may be required for other purposes
i. alien species are difficult to control
j. species close to extinction are harder to conserve
k. management/protection may represent a significant cost
Examiners report
Vinegar is a water-based solution of ethanoic acid. Acetobacter aceti is used in the production of vinegar. This bacterium has the ability to convert ethyl alcohol, C2H5OH, into ethanoic acid, CH3COOH.
In the generator method of ethanoic acid fermentation, Acetobacter aceti are grown over wood shavings in a fermenter to the point where they form a biofilm.
At the base of the fermenter oxygen is bubbled in, which then rises through the wood shavings. Ethanol drips through the wood shavings. At a suitable temperature the ethanol is converted to ethanoic acid, which is withdrawn from the bottom of the fermenter, and new ethanol is added at the top.
A. aceti is a Gram-negative bacterium. If a Gram staining procedure were carried out on a sample of A. aceti, predict the result that would be observed after decolourization.
A. aceti is a Gram-negative bacterium. If a Gram staining procedure were carried out on a sample of A. aceti, predict the result that would be observed after counterstaining.
List two abiotic variables that would need to be monitored during this fermentation process.
Describe one way in which microorganisms in this fermenter could be limited by their own activities.
Distinguish between batch fermentation and continuous fermentation.
Outline the concept of an emergent property.
Markscheme
the bacteria would be clear/colourless
would stain pink
Do not accept “violet” or “lilac”.
a. oxygen
b. temperature
c. pH levels
d. CO2
a. name of a factor
b. description
eg
a. pH
b.lowered by «ethanoic» acid production.
eg
a. increase in temperature
b. due to metabolism.
eg
a. increased population size/reproduction
b. would limit resources.
eg
a. increased metabolic waste
b. reduce population.
Table format is not required.
a. emergent properties arise from the interaction of the elements of a system
b. behaviours exhibited which are not shown by individuals
c. quoroum sensing
OR
matrix production
OR
water channels
OR
antibiotic resistance
OR
other correct example
Examiners report
Chthamalus and Balanus are two species of barnacles that live attached to rocks between the low and high tide level of the sea. The distribution of each species is influenced by the presence of their own species and different species.
Distinguish between a fundamental niche and realized niche.
Suggest reasons that Chthamalus cannot live higher up the shore.
Describe how the distribution of Chthamalus and Balanus is affected when both are present.
Markscheme
realized is actual niche, fundamental is potential niche
a. must spend some of their time under water / prevent dehydration
b. need water for food/nutrients
c. need water for reproduction
d. more accessible to their predators
e. there are no rocks for them to live on
OR
there is no suitable habitat for them
a. Chthamalus and Balanus / both have a reduced distribution
b. they are in competition for part of the habitat on the rock
c. Balanus occupies some of the habitat of the fundamental niche of Chthalamus
OR
where the fundamental niche overlaps Balanus prevails/survives
d. the distribution of Balanus is unchanged in areas colonized by Chthalamus
e. Balanus is in competition with other species closer to low water
Examiners report
The number of plants in two fields of approximately the same size was counted.
Compare and contrast the richness and the evenness of the two fields.
A calculation of Simpson’s reciprocal index was undertaken on each field with the following results.
Evaluate these results.
Markscheme
a. same richness as they have the same number of species/total of individuals
b. field 1 has more evenness as more even distribution of numbers among the species. Allow vice versa.
a. the higher the number the more diverse/biodiverse is the field
OR
b. field 1 shows greater diversity/biodiversity (as it has a higher value)
Examiners report
In 1997 in South Africa, a decision was made to decrease the use of mosquito-killing pesticides due to their negative effect on the environment. Mosquitoes are known to be responsible for the spread of malaria. In 2001 the decision was reversed and the use of pesticides was increased. The graph shows the estimated numbers of people with malaria in each year.
Outline the trend in the number of people with malaria during the period when the use of pesticides was decreased in South Africa.
One pesticide used in killing mosquitoes was DDT. Considering its harmful effects, discuss whether the decision to reintroduce it was justified.
Markscheme
the number of people with malaria increased
a. choice has to be made between damage to environment or increase in malaria
b. DT may lead to biomagnification/bioaccumulation in food chains
OR
taken up by species in lower trophic levels becoming more concentrated at higher trophic levels
c. causes harm to consumers at end of food chain
OR
example «eg: thin egg shells of falcons»
d. DDT is shown to be effective in reducing malaria
e. possible partial solution to be selective in areas sprayed with DDT
f. may kill insects that are not pests
Examiners report
After their introduction cane toads (Rhinella marina) have become a serious pest in many parts of Australia. In an attempt to control them scientists set traps to which they added toxins produced by native species of toad to capture cane toad tadpoles. The toad toxin attracts the cane toad tadpoles without killing them.
Outline one consequence of introducing an alien species into an ecosystem.
State the origin of cane toads.
Evaluate the use of traps containing toxin as a means of cane toad control.
Markscheme
a. uncontrolled increase of numbers «in alien species»
OR
become invasive
OR
have no «natural» predators
b. outcompetes native species / reduces biodiversity
OR
carries disease
OR
preys on local species decreasing population size
OR
disrupts food chains/webs
Central/South/Latin America
a. the baited traps catch a lot more tadpoles than the unbaited traps / traps with bait are more effective than those without
b. baited traps are almost 20 times more effective
c. traps without toxin reach capacity sooner than those with toxin
d. there may be environmental/health/safety problems with the toad toxin used
e. there is no information on how toads are controlled since the toxin does not kill the tadpoles
Examiners report
Reef-building corals are an association between two organisms: coral polyps and Zooxanthellae.
State the relationship between Zooxanthellae and coral reef species.
Describe the exchange of materials between the coral’s polyps and Zooxanthellae.
State one limiting factor on Zooxanthellae which affects coral reef formation.
Markscheme
mutualism
a. polyp is a source of carbon dioxide for the Zooxanthellae
OR
polyp is a source of ammonia/nitrogen for the Zooxanthellae
b. Zooxanthellae provide oxygen to the polyp
OR
Zooxanthellae provide sugars/glucose/glycerol/lipids/amino acids to the polyp
light / temperature / salinity / carbon dioxide / pH
Examiners report
Explain the use of indicator species to assess the condition of the environment.
Markscheme
a. indicator species are organisms that indicate health of ecosystem/level of pollution
b. they exist in higher relative numbers under certain environmental conditions
OR
if certain environmental conditions are not found, indicator species die/reproduce
c. are very sensitive/highly tolerant species
d. provides quantitative information on the quality of the environment around it
e. named example of indicator species and susceptibility
Must state a named species. eg: Lichens used to detect air quality.
f. indicator species are used to calculate biotic index
Examiners report
The climograph shows the distribution of biomes according to the temperature and rainfall of land areas on Earth.
Identify the ecosystem with the appropriate numeral from the climograph.
Referring to the climograph, explain reasons that the nutrient store in the litter layer of the taiga is greater than in the tropical rainforest.
Markscheme
Award [2] if all three are correct, [1 max] if one or two are correct and [0] if none correct.
a. litter is dead plant material on the ground
b. conditions in tropical rainforests are ideal to decompose plant material
OR
conditions in taiga do not favour decomposition of litter
c. decomposition returns nutrients to soil
OR
nutrients in taiga remain in the litter and not in the soil
d. tropical rainforests have more saprotrophs/decomposers
OR
taiga have fewer saprotrophs/decomposers
Numbers alone do not constitute an explanation.
Examiners report
The Gersmehl diagram below shows the movement and storage of nutrients in a taiga ecosystem.
Predict the possible effect of global warming on the nutrient flow in a taiga ecosystem.
Markscheme
a. increased biomass «with higher temperatures»
b. «so» increased uptake of nutrients from soil «into the biomass»
c. increased decomposition of litter «due to growth of decomposers»
d. «so» increased nutrient composition of soil «L→ S»
e. increased weathering of rocks «increasing minerals in soil»
f. weather changes cause increased runoff from litter/leaching from soil
Examiners report
Ecologists studied the distribution of five species of insectivorous wood warblers of the genus Dendorica living on different parts of coniferous trees in mature forests.
Distinguish between the distribution of D. tigrina and that of D. coronata.
Outline the principle of competitive exclusion.
Other than position in the tree, suggest two ways in which the niches of the warblers in the ecosystem may differ.
1.
2.
The diagram shows the realized niches of the five species of warbler. Suggest how the fundamental niche of D. castanea might differ from its realized niche.
Markscheme
a. D. tigrina lives higher in the tree than D. coronata;
b. D. coronata occupies a greater area/height range than D. tigrina;
c. D. tigrina found in the outer regions and D. coronata found on the inside;
Accept vice-versa.
a. no two species can occupy the same niche;
b. competition between them would cause one species to drive the other out
OR
one of the two species would need to adapt and evolve accordingly;
a. different food/prey;
b. different predators;
c. active at different times of the day;
d. present at different times of the year;
e. different nest sites;
f. different temperatures;
Do not accept “different habitats”.
a. the realized is the actual niche and the fundamental is in the absence of competition;
b. with no competition the D. castanea would have a larger habitat/more food
OR
D.castanea could occupy the niches currently occupied by the other warbler species;
Accept named species.
Examiners report
Overall, well answered.
When describing competitive exclusion many candidates simply described competition. Some mentioned habitat rather than niche.
Weaker candidates gave incomplete or confused suggestions in differentiating between the realised and fundamental niche.
The fire ant (Solenopsis geminata) is an effective colonizer and has become invasive in a number of ecosystems. Sometimes, efforts to eliminate this species have had an unexpected impact on community structure. It is argued that S. geminata can play a beneficial role in corn production. The graph shows how the presence of S. geminata
can impact insect diversity in areas where crops of corn are grown.
State the impact of S. geminata on insect species diversity.
Discuss whether S. geminata might play a positive role in corn production.
Researchers have argued that S. geminata is a keystone species in the corn agricultural system. Outline what is meant by a keystone species.
Markscheme
reduction in number of species/richness/diversity
a. biological control of/reduction in corn pests
b. reduction in the use of pesticides
c. damage on beneficial species OWTTE
d. reduction in insect diversity can have broad ecosystem negative impact
OR
example of negative effect
e. long-term effects unknown
definition
a. keystone species is one in which presence has a disproportionate impact on the ecosystem
impact
b. removal often leads to significant changes
OR
valid example
Examiners report
Plastic has accumulated in marine environments and is now causing problems for wildlife. Some marine birds have become entangled in plastic debris and some have been harmed by ingesting it. The table shows the extent of the problem worldwide in different groups of birds.
[Source: BIO Intelligence Service, 2011. Plastic Waste in the Environment. [pdf]
European Commission. Available at: http://ec.europa.eu/environment/waste/studies/pdf/plastics.pdf.]
Calculate the number of species of grebe with problems due to entanglement.
Suggest how entanglement in plastics can lead to the death of marine birds.
Identify the group with the greatest number of species with problems due to ingestion of plastics.
Describe how ingested plastics can cause problems to marine birds.
Markscheme
2;
a. birds are unable to fly/swim for food;
b. unable to escape predators;
c. birds drown;
d. birds suffocate / are strangled;
C / albatrosses, petrels and shearwaters;
a. fill up the stomachs (of young birds) so they feel full / starve to death;
b. damage the digestive system / cut the gut/stomach/oesophagus/intestines (leading to internal bleeding);
c. block passage of food (causing starvation);
d. cause choking (so cannot breathe);
e. contain/decompose to toxic chemicals (poisoning birds)
OR
toxins/microplastics in seawater build up/biomagnify (and poison wildlife);
Examiners report
This question outlining how plastic pollution affects marine birds was straightforward for all candidates.
Data from the International Union for Conservation of Nature (IUCN) indicates that the population numbers of many mammal species are decreasing. The chart shows reasons for the decrease and the number of species in each category of danger.
[Source: Michael Hoffmann et al. 2011. The changing fates of the world’s mammals. Philosophical Transactions of the Royal Society B, Volume 366, issue 1578. DOI: 10.1098/rstb.2011.0116. By permission of the Royal Society.]
Calculate how many species are classified as endangered due to hunting and trapping.
State one reason mammals can continue to survive even if they are extinct in the wild.
Outline how deforestation can affect the richness of biodiversity in an ecosystem.
Explain the impact of plastic waste on Laysan albatrosses (Phoebastria immutabilis).
Markscheme
14/15/16
Do not accept intermediate values eg: 14.5
zoos/nature reserves/captive breeding/ex situ conservation/farming/husbandry/pets
deforestation reduces richness by destroying habitat/loss of food/shelter/nesting sites
a. adults/young ingest plastic «which is indigestible»
b. plastic damages/fills stomach «can lead to starvation and death»
c. plastic blocks intestine so food cannot be digested «can lead to starvation and death»
d. adults/young can become entangled in plastic and so they drown/choke/suffocate
Allow other verifiable effect of plastic
“Can kill the birds” is too vague and worth [0]
[Max 2 Marks]
Examiners report
The table shows the number of crabs found in two rockpools by the coast. There were 16 crabs in total in each rockpool.
[Source: © International Baccalaureate Organization 2020.]
Two components of biodiversity are richness and evenness. Deduce which of the two pools was higher in richness.
Two components of biodiversity are richness and evenness. Deduce which of the two pools was higher in evenness.
Calculation of Simpson’s reciprocal diversity index for both rockpools gives the following results.
Outline what conclusion can be drawn from the results.
The graph shows how the number of ant species found on isolated islands near New Guinea depends on the size of the island.
[Source: University of Windsor, The Theory of Island Biogeography. Available at:
http://web2.uwindsor.ca/courses/biology/macisaac/55-437/lecture9.htm.]
Explain the relationship between island size and number of ant species.
Markscheme
A;
B;
B is more diverse/biodiverse than A;
Accept vice-versa. Do not accept greater Simpson’s reciprocal diversity index.
(the larger islands contain) more species as there are more habitats;
Examiners report
Candidates could deduce the richness and evenness of the pools but gave incomplete answers to the other two parts of this question.
The conclusion from the table showing values of Simpson’s reciprocal diversity index required mention of biodiversity, not simply that one pool is more diverse.
The graph showing the number of ant species according to island size required an explanation of the graph. Many candidates simply stated the relationship with no explanation.
Explain what information a pyramid of energy provides about an ecological community.
Markscheme
a. shows the amount of energy at each trophic level (of a food chain/web);
b. (energy) measured over a period of time/year
OR
units are energy per area per time/kJ m–2 year–1;
c. the width/size of each bar represents the amount of energy;
d. the bottom level represent the producers;
e. subsequent levels represent consumers;
f. each level should be roughly one tenth of the size/10 % of the preceding level;
OR
organisms at the top of the food chain are shown to have much less energy available to them;
g. the energy that enters a community is ultimately lost as heat/in respiration
Some answers may be displayed in a diagram.
Examiners report
The better candidates performed well in this question while weaker candidates are still confused by pyramids of energy. Many referred to numbers, or biomass at each trophic level. Very few candidates stated that the measurements were taken over a period of time.
The sea snail Nucella ostrina and the sea star Pisaster ochraceus are predators of the mussel Mytilus trossulus. The mussels live on rocks at the edge of the sea and feed on phytoplankton and zooplankton. The zooplankton feed on the phytoplankton.
Groups of 50 mussels were transplanted to an experimental area and protected from predation until the start of the experiment. Researchers then investigated the effect of the predators on the population of the mussels over a period of 60 days.
[Source: Republished with permission of John Wiley and Sons, from Navarrete, S. A. and Menge, B. A. (1996),
Keystone Predation and Interaction Strength: Interactive Effects of Predators on Their Main Prey. Ecological Monographs, 66: 409–429. doi:10.2307/2963488; permission conveyed through Copyright Clearance Center, Inc.]
Compare and contrast the effects of the predators on the population of the mussels.
The sea star also eats the sea snails. Construct a food web to show the feeding relationships between these five organisms in the ecosystem.
Markscheme
a. both cause the frequency of the mussel to decrease
b. sea star affects the mussel population more than the sea snail
c. when both are together the effect of the sea snail is low
Accept binomial names
Allow numerical answers if expressed as comparisons and the candidates are not simply stating numbers
[Max 2 Marks]
Award [2] for a correct food web
Award [1] for phytoplankton, zooplankton and mussel with correct arrows
Award [1] for mussel, sea snail and sea star with correct arrows
Award [0] if arrows are in wrong direction
Accept binomial or scientific names
Examiners report
Explain reasons for differences in the realized niche and fundamental niche of an organism.
Markscheme
a. an ecological niche is an organism’s role/functional place in the environment
b. the fundamental niche is the potential niche and the realized niche is the actual niche
c. includes habitat/feeding/how it survives
d. limiting factors play a part on the actual distribution of species
e. competition prevents species occupying their fundamental niche
f. species show competitive exclusion
OR
two species cannot occupy the same niche in an ecosystem
g. «in competitive exclusion» one species will replace the other species
The answers given in the markscheme may be awarded if the candidate explains a suitable example
For marking point g, do not accept “one species becomes extinct” as a standalone answer unless it is clear they
are referring only to the ecosystem under discussion
[Max 4 Marks]
Examiners report
Wisconsin Department of Natural Resources has issued guidelines to control invasive plants within the state. One mechanical method is to cut the plants down where they occur. However the time of year the plants are cut down is important in their control. The chart shows the months when it is recommended to cut down the plants and the months when they should not be cut down.
State which plant can be cut in August.
Suggest a reason for not cutting invasive plants at certain times of year.
Outline reasons for controlling invasive plants.
Discuss what precautions should be taken before considering biological control of the invasive plants.
Markscheme
Japanese stiltgrass ✔
produce seeds which spread when cutting
OR
avoid vegetative proliferation/cloning
OR
may provide habitats for other species ✔
Accept any other reasonable answer
a. «biotic» competition with native plants
OR
disrupt the food chain/ecosystem ✔
b. competition for abiotic factors ✔
Accept competition for light/space/water/etc for b
c. reduce competitive exclusion / avoid overlapping niches ✔
d. can cause changes to soil ✔
eg: Rhododendrons/conifers acidify the soil, making it difficult for other species to grow
e. break/damage/cause death/extinction of native plants ✔
a. «control» introduced species should only target alien plants
OR
«control» introduced species should not outcompete endemic species ✔
b. should not upset food chains/habitats ✔
c. should have some natural control/predator ✔
d. should not spread outside required area/not become invasive themselves
OR
field testing for effectiveness ✔
Examiners report
When water rises above a certain temperature, coral bleaching may occur. The coral expels Zooxanthellae algae living in its tissues, leaving the coral a white colour. The graph shows how the water temperature is changing in the coral reefs surrounding the Cayman Islands.
State the trend in temperatures from 1982 to 2014.
Deduce the effect of bleaching on corals.
Markscheme
«overall» water temperature increasing
OR
the range of fluctuations increases ✔
Do not accept the trend is fluctuating
a. the coral and the algae have a symbiotic/mutualistic relationship
OR
two different organisms live together and depend on each other ✔
b. algae expelled from coral/relationship broken ✔
c. coral produces carbon dioxide from respiration ✔
d. the algae use the carbon dioxide to carry out photosynthesis/produce nutrients ✔
e. without the nutrients from the algae the coral are liable to starve ✔
f. coral dies/is susceptible to disease ✔
Do not accept effects on species other than coral
Examiners report
Distinguish between fundamental niche and realized niche.
Outline the impact of competition on the niche of an organism.
Outline the characteristics of keystone species in an ecosystem.
Markscheme
fundamental is the potential (niche) and realized is the actual (niche)
OWTTE.
a. competition can limit the niche
b. competition can limit resources
c. when competition is removed the niche can expand
d. can result in exclusion or removal of a species from a niche / only one species can occupy a niche
a. keystone species has a strong/disproportionate effect on a community/food web/ecosystem
b. absence of keystone species would completely alter the ecosystem
Examiners report
The food conversion ratio (FCR) is the ratio between the mass of food given to a farmed animal and its corresponding increase in mass. The first bar chart shows the FCR for four farmed animals. The second bar chart shows the percentage yield of edible meat provided by each whole animal.
Calculate the increase in mass of a cow given 6 kg of food
Calculate how much food would be required to produce 20 kg of boar meat.
With reference to the data, discuss the farming of salmon for sustainable food production.
Markscheme
1 kg ✔
Working not required
120 kg ✔
Working not required
a. small amount of/least food resources used in production ✔
b. high yield means less energy lost in respiration
OR
high yield means less waste of inedible material ✔
c. other resources/cost of production/nutritional values not mentioned ✔
eg: habitat, heating, water
d. sustainability requires knowledge of the effect on the environment/pollution/contamination of water supply
OR
sustainability requires minimal use of drugs/chemicals/antibiotics ✔
e. example of ethical issue ✔
eg: it may spread diseases to wild population
Examiners report
A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.
[Source: climatica.org.uk]
Predict the process of succession that takes place on exposed bare ground as the glacier retreats.
Suggest how human activities could impact the development of an ecosystem on exposed bare ground.
Markscheme
a. (bare ground) colonized by microorganisms/pioneer species
b. thin soil forms from rock fragments/decomposing organisms
c. soil retains water (from melting permafrost/ice)
d. grasses/small plants/herbaceous plants/grow
e. (larger plants) create habitats for animals
f. weather/climate may limit plant size/biodiversity
OR
climax community forms
a. buildings/roads/walking prevent plant cover/soil development/cause soil erosion
b. may destroy moss/soil organisms / damage emerging vegetation
c. introduce alien species
d. rubbish/solid waste/pollution may impede natural development
e. feces/excrement may contribute to/alter soil development / add fertilizer/pesticides to increase growth of plants
f. sow seeds/planting and so alter diversity
g. irrigation/drainage to affect growth
Examiners report
Paramecium aurelia and Paramecium caudatum are single cell organisms. They were grown separately and together. The population growth curves are shown.
Explain the results shown in this experiment.
Markscheme
a. when they are alone they both show a greater population than when together
b. two species cannot survive indefinitely in the same habitat if their niches are identical
OR
competitive exclusion
c. Paramecia compete for food/space
d. P. caudatum starts to disappear/decrease after day 6–8 days «whereas P. aurelia reaches a plateau» Vice versa
OR
the population of P.caudatum decreases much more than the population of P.aurelia
e. P. aurelia is better suited/fitted than P. caudatum
Examiners report
The pyramid of biomass obtained from a pine forest stream includes the parasite biomass. Parasites are fungi, worms and other organisms that live on a host.
Estimate the approximate amount of biomass represented by parasites in this ecosystem.
Compare and contrast the biomass in the different trophic levels.
Outline the reason that parasite biomass occurs in both tertiary consumers and secondary consumers.
Markscheme
any value between 15 kg and 22 kg
a. biomass decreases going up the trophic levels ✓
b. autotrophs have greatest biomass «around 40 040 kg»
OR
tertiary consumers have the least biomass ✓
c. greatest loss of biomass is from autotrophs to primary consumers
parasites feed on secondary and primary consumers
Examiners report
Calculate the energy loss due to respiration in primary consumers in kJ m–2 y–1.
Outline why a year is more suitable than a month for the measurement of energy flow.
Explain how pesticides may undergo biomagnification in the lake.
Markscheme
190
accounts for different productivity at different times of year/seasonal variations
OR
more data collected
OR
to increase reliability
OR
trends over time more easily detected
a. the increase in concentration of the pesticide at higher trophic levels
b. taken in by organisms low in the food chain
c. cannot be excreted so remains in tissues
OR
accumulates as more organisms from lower levels are eaten
d. pesticides do not degrade/degrade very slowly
[Max 2 Marks]
Examiners report
A biotic index allows water pollution to be monitored without the need for a large number of chemical tests. Aquatic invertebrates are assigned pollution tolerance levels and these are used to assess water quality. The amount of each invertebrate species in the water is measured and this is used to calculate the index. The tolerance level of three invertebrate species is shown.
State which species could be found in mildly polluted water.
State the name given to organisms whose presence or absence reflects an environmental condition.
Distinguish between richness and evenness as components of biodiversity.
Explain how edge effects can influence biodiversity in a region.
Markscheme
dragonfly nymph AND midge larva (Both needed)
OR
all except mayfly ✔
indicator species ✔
richness is how many species there are in an area while evenness is how similar in number the populations of each species are ✔
a. the edge of an ecosystem has different features from the centre ✔
eg: amount of wind, light
b. the edge has greater biodiversity ✔
c. it is an area of overlap between two ecosystems/habitats ✔
d. it has species from both ecosystems
OR
it has species not found in either ✔
e. reduction in biodiversity due to human interference ✔
Examiners report
One challenge associated with establishing nature reserves is concerns about edge effects. The graph shows that some edge effects in the Amazon rainforest are detected quite far in from the edge.
Determine how far from the forest edge an increase in disturbance-adapted beetles would be detected.
With respect to the example of disturbance-adapted beetles, explain what is meant by an indicator species.
Outline how reserve size and shape can impact edge effects.
Markscheme
200 m / 0 to 200 m
Units required.
a. species whose numbers/abundance are affected by a particular environmental condition
OR
species used to assess a specific environmental condition
b. «the presence of disturbance adapted beetles» indicates that the environment has been disturbed
c. «the presence of disturbance adapted beetles» indicates that there is an edge «within 200 m»
a. small reserve has greater edge «relative to area therefore more edge effects»
b. changing shape can change edge length/perimeter for a given area «changing edge effects»
c.«at the edge there is» interaction of two communities
OR
different species may be better at invading into neighbouring community
OR
edge favors disturbance-adapted species
OWTTE.
Examiners report
Isopods are a group of organisms belonging to the arthropods and include woodlice (slaters) and other species, some of which live on land and others in water. A study was carried out on the diversity of isopod species living in a bog (site B), the edge zone separating the bog and forest (site E) and adjacent forest (site F).
Data collected for the three sites are summarized in the table:
Outline what is meant by the edge effect.
Analyse the differences in biodiversity seen in the three sites.
State one method that could be used to estimate the isopod population size.
Markscheme
a. occurs at the boundary between two ecosystems/habitats
b. gradient of abiotic conditions at the edge
c. (as a result) community differs at the edge
d. community at the edge is more diverse than adjacent communities
a. number of individuals differs more than number of species between the zones
b. zone E has lowest diversity / zone F has highest diversity
c. zone B has higher diversity than zone E
d. edge effect is evident
capture-mark-release-recapture
OR
quadrat / transect
Examiners report
Discuss the health consequences and environmental consequences of the use of DDT.
Markscheme
a. DDT is a pesticide/insecticide
b. reduction in disease vectors
OR
reduction in mosquitos carrying malaria
c. leading to a reduction in disease/malaria rates
Accept other diseases such as typhus carried by lice.
d. biomagnification in food chains
e. negative impact on health of top predators / example of top predator
f. thin eggs shells
OR
reduced reproductive success in birds of prey
Examiners report