Topic 4 + C: Ecology Review [61 marks]

1. [1 mark]In an area of forest measuring 100 m by 100 m, samples were taken to estimate the number of silver maple (Acer saccharinum)trees in the forest. The number of trees counted in each of five areas of 400 m was recorded.

Approximately how many silver maple trees are in the 10000m area of forest?

A. 5

B. 25

C. 125

D. 625

MarkschemeC

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2. [1 mark]The diagram shows the carbon cycle.

[Source: © International Baccalaureate Organization 2017]

Which two processes correspond to the labelled arrows?

A. K is combustion and L is catabolism.

B. J is anabolism and K is respiration.

C. J is combustion and K is respiration.

D. J is anabolism and L is catabolism.

MarkschemeC

3. [1 mark]Euglena is a unicellular organism that feeds on bacteria and uses CO as a carbon source. Which describes the nutrition of thisorganism?

A. Autotrophic only

B. Heterotrophic only

C. Saprotrophic only

D. Autotrophic and heterotrophic

MarkschemeD

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4. [1 mark]The diagram shows a version of the carbon cycle. What is indicated by the numbers?

MarkschemeC

5. [1 mark]Which characteristic of water vapour classifies it as a greenhouse gas?

A. It absorbs and then re-emits some of the long wave radiation emitted by the Earth’s surface.

B. It prevents short wave radiation from reaching the Earth’s surface.

C. It absorbs UV radiation but does not re-emit it.

D. It absorbs infra-red radiation but does not re-emit it.

MarkschemeA

6. [1 mark]What is lost between trophic levels in ecosystems and cannot be recycled?

A. Heat

B. Nitrogen

C. Carbon compounds

D. Biomass

MarkschemeA

7. [1 mark]What favours the production of peat?

I. Presence of organic matter

II. Anaerobic conditions

III. Acidic conditions

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

MarkschemeD

8. [1 mark]By which mechanism do greenhouse gases contribute to global warming?

A. Their higher concentration absorbs more long wave radiation coming from the Sun.

B. Short wave radiation emitted from the Earth’s surface increases with their concentration.

C. They absorb higher amounts of long wave radiation emitted from the Earth’s surface as their concentration increases.

D. They absorb higher amounts of short wave radiation caused by increased combustion of fossilized organic matter.

MarkschemeC

9. [1 mark]Methanogens produce methane gas. What is this gas converted to in the atmosphere?

A. Carbon dioxide and oxygen

B. Ethanol and carbon dioxide

C. Carbon monoxide and ozone

D. Carbon dioxide and water

MarkschemeD

10. [1 mark]The image shows a transect through a stream and a field.

Which calculation would test for the association between two species of plants from quadrat data from section A and section B of the field?

A. Correlation coefficient

B. Random numbers sampling

C. Standard deviation

D. Chi-squared

MarkschemeD

11. [1 mark]What is the classification of an organism that is able to make organic compounds from inorganic nutrients?

A. AutotrophB. ConsumerC. DetritivoreD. Saprotroph

MarkschemeA

12. [1 mark]What restricts the length of a food chain?

A. Energy losses between the trophic levelsB. A greater biomass at the higher trophic levelsC. The number of species in the food webD. The consumption of waste by detritivores

MarkschemeA

13. [1 mark]Which are characteristics of a species?

I. The potential to interbreed to produce fertile offspring II. The formation of a population with members of the same species within a community III. The overproduction of offspring

A. I and II onlyB. I and III onlyC. II and III onlyD. I, II and III

MarkschemeA

14. [1 mark]The statement is about the role of some bacteria in ecosystems.

What is the mode of nutrition of these bacteria?

A. They are autotrophs.B. They are consumers.C. They are saprotrophs.D. They are detritivores.

MarkschemeC

15. [1 mark]The diagram represents a pyramid of energy.

What level does the letter X represent?

A. LightB. Primary consumersC. Abiotic environmentD. Producers

MarkschemeD

[1 mark]16. Calculate the energy loss due to respiration in primary consumers in kJ m y .

Markscheme190

–2 –1

[2 marks]17.

The sea snail Nucella ostrina and the sea star Pisaster ochraceus are predators of the mussel Mytilus trossulus. The mussels live onrocks 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.

Markschemea. 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]

[1 mark]18a.

Data from the International Union for Conservation of Nature (IUCN) indicates that the population numbers of many mammal speciesare 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.

Markscheme14/15/16

Do not accept intermediate values eg: 14.5

[1 mark]18b. Outline how deforestation can affect the richness of biodiversity in an ecosystem.

Markschemedeforestation reduces richness by destroying habitat/loss of food/shelter/nesting sites

[2 marks]18c. Explain the impact of plastic waste on Laysan albatrosses ( Phoebastria immutabilis).

Markschemea. 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]

[1 mark]19a.

To assess the impact of introduced cats (Felis silvestris) that prey on native species, a study was carried out on 120 islands around theworld. The graph shows the impact of F. silvestris on reptiles, birds and mammals.

[Source: A global review of the impacts of invasive cats on island endangered vertebrates, F. M. Medina et al. (2011) Global ChangeBiology, 17, pp. 3503–3510. Reproduced with permission from John Wiley and Sons.]

Identify how the pattern in mammals is different from reptiles and birds.

Markschemea. more extinct than endangered «in mammals as opposed to reptiles and birds»

b. total percentage extinct plus endangered mammals lower than reptiles and birds

[Max 1 Mark]

[2 marks]19b. Describe how invasive species such as F. silvestris can have a significant impact on native species.

Markschemea. cats/invasive species compete with native species for food/habitat/resources

OWTTE

b. invasive species/cats may reduce/endanger native populations

c. invasive species/cats may change the structure/balance of the food web/chain

[Max 2 Marks]

[1 mark]19c. Suggest a method to limit the impact of F. silvestris on native species.

Markschemea. control population/sterilization «of cats»/culling/hunting

b. keep household cats indoors

[Max 1 Mark]

[1 mark]19d.

The ‘Ua‘u petrel (Pterodroma sandwichensis) is considered to be an indicator species in the Hawaiian Islands.

[Source: https://commons.wikimedia.org/wiki/File:Oestrelata_phaeopygia_AvesHawaiienses00Wils_0382.jpg]

State the role of an indicator species.

Markschemea. early warning system

b. provide information on environmental conditions/ecosystem

OWTTE

[Max 1 Mark]

[1 mark]20.

Native oyster populations are decreasing where rivers meet the ocean along the northwest coast of North America. These oysterpopulations are being attacked by a gastropod.

It is known that oysters and gastropods have hard parts composed of calcium carbonate and that ocean acidification is increasing.Studies were carried out using juvenile oysters and gastropods to investigate the effects of acidification on the decrease in thepopulation of oysters.

The first step was to raise oysters in two different mesocosms. One had seawater at a normal concentration of CO and the other hadsea water with a high concentration of CO . Gastropods were raised in two further mesocosms with normal and high COconcentrations respectively.

Outline how acidified sea water could affect the shells of the oyster.

MarkschemeShells might dissolve/deteriorate / become smaller/thinner/weaker / OWTTEORshell formation reduced / more difficult

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[1 mark]21a.

The image shows a food web.

Using the food web, identify a detritivore.

Markschemeearthworm/woodlouse

[1 mark]21b. Using the food web, identify a saprotroph.

Markschemebacteria/fungi

Do not accept protozoans or nematodes as they are consumers.

[3 marks]21c. Outline the energy flow through this food web.

Markschemea. light energy of Sun is converted by plant/autotroph to chemical energy «in carbon compounds through photosynthesis»

b. detritivores/saprotrophs decay plant material «that accumulates in the soil» to obtain energy OWTTE

c. consumers release energy from the carbon compounds by cell respiration energy lost as heat

d. energy is used by organisms for metabolism

e. energy is transferred between organisms/trophic levels through the food chains/web For mp e, accept specific example such as energy is transferred from primary to secondary consumer etc .

f. energy is lost at each trophic level «so lengths of food chains/web are restricted»ORapproximately 80/90 % of energy is lost «between trophic levels»Vice versa

Award mark points that refer to the specific organisms from this food web.

[1 mark]22a.

Reef-building corals are an association between two organisms: coral polyps and Zooxanthellae.

State the relationship between Zooxanthellae and coral reef species.

Markschememutualism

[2 marks]22b. Describe the exchange of materials between the coral’s polyps and Zooxanthellae.

Markschemea. polyp is a source of carbon dioxide for the Zooxanthellae ORpolyp is a source of ammonia/nitrogen for the Zooxanthellae

b. Zooxanthellae provide oxygen to the polypORZooxanthellae provide sugars/glucose/glycerol/lipids/amino acids to the polyp

[1 mark]22c. State one limiting factor on Zooxanthellae which affects coral reef formation.

Markschemelight / temperature / salinity / carbon dioxide / pH

23. [2 marks]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.

Markschemea. 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

[1 mark]24a.

After their introduction cane toads (Rhinella marina) have become a serious pest in many parts of Australia. In an attempt to controlthem scientists set traps to which they added toxins produced by native species of toad to capture cane toad tadpoles. The toad toxinattracts the cane toad tadpoles without killing them.

State the origin of cane toads.

MarkschemeCentral/South/Latin America

[3 marks]24b. Evaluate the use of traps containing toxin as a means of cane toad control.

Markschemea. 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

[2 marks]25a.

Freshwater invertebrates were sampled by students at three sites along a river in central France. The animals were identified andcounted. 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.

Markschemea.

b. = 3.56 «allow 3.55»

25b. [2 marks]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 speciespresent.

Markschemea. 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

[4 marks]25c. Discuss the advantages and disadvantages of in situ conservation methods.

MarkschemeAdvantages: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

26. [3 marks]Paramecium aurelia and Paramecium caudatum are single cell organisms. They were grown separately and together. Thepopulation growth curves are shown.

Explain the results shown in this experiment.

Markschemea. 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 identicalORcompetitive 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 versaORthe population of P.caudatum decreases much more than the population of P.aurelia

e. P. aurelia is better suited/fitted than P. caudatum

[3 marks]27a. Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant.

Markschemea. example eg: DDT / mercury / cadmium

b. substance accumulates in «fat» tissue/not excreted «when consumed»

c. contaminated organisms consumed «in large quantities» by higher level consumers

d. pollutant becomes more concentrated at each higher trophic level / through the food chain

e. some pollutants are more likely to be biomagnified «accumulate in fat tissue»ORsome organisms are more likely to be affected by biomagnification than othersORbiomagnification not the same at each trophic level

Only [2] if verified example not given.

[1 mark]27b. Determine whether islands are open or closed ecosystems.

Markschemeclosed because islands do not exchange matter/nutrients with surroundingsORopen because islands do exchange matter/nutrients with surroundings

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28a. [1 mark]Zoos devote much effort to preserving and breeding elephants in captivity. Data for births resulting from artificial insemination inzoos in the United States from 1960 to 2012 are shown below.

54% of successful artificial inseminations have resulted in miscarriages, stillborn births or premature deaths.

Evaluate the success rate of breeding elephants by artificial insemination using these data.

Markschemea. «not very successful as» less than half of the artificial inseminations have resulted in live births

b. there are no data for artificial insemination that did not result in pregnancy / no data for normal breeding success «in zoos»

Accept answers in the converse: «not very successful as» more than half do not result in live births

[2 marks]28b. Discuss two advantages of ex situ conservation measures.

Markschemea. raise awareness / gain widespread public/political support for conservation actions

b. breed endangered species in captivity «for reintroduction»

c. education/research opportunities

d. lower maintenance/cost than in situ conservation

e. protect endangered species