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.
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 At a suitable temperature the ethanol is converted to ethanoic acid, which is withdrawn from the bottom of the fermenter, and new ethanol is added at the top.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.
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.
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.
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.
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.
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.
Explain the use of indicator species to assess the condition of the environment.
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.
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.
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.
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.
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.
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).
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.
Explain what information a pyramid of energy provides about an ecological community.
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.
Explain reasons for differences in the realized niche and fundamental niche of an organism.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Discuss the health consequences and environmental consequences of the use of DDT.