| Date | November 2017 | Marks available | 2 | Reference code | 17N.3.SL.TZ0.13 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Construct | Question number | 13 | Adapted from | N/A |
Question
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
Syllabus sections
- 17N.3.SL.TZ0.12a: Calculate the energy loss due to respiration in primary consumers in kJ m–2 y–1.
- 17M.3.SL.TZ2.16a: Estimate the approximate amount of biomass represented by parasites in this ecosystem.
- 17M.3.HL.TZ1.14e: Determine whether islands are open or closed ecosystems.
- 17M.3.HL.TZ2.15b: State the trophic level of Zooxanthellae.
-
18M.3.HL.TZ1.15a:
A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.
State one abiotic factor that will determine the type of ecosystem in a succession.
- 19M.3.HL.TZ2.15a.iii: Using the climograph, outline the pattern of rainfall.
- 18M.3.SL.TZ1.14b: Suggest how human activities could impact the development of an ecosystem on exposed bare...
- 19N.3.SL.TZ0.12b: Distinguish between the transfer of matter and energy in closed ecosystems.
- 18N.3.HL.TZ0.14a: Each of the mesocosms is an open ecosystem. State the property that makes the mesocosms open...
- 18N.3.HL.TZ0.14c: Outline top-down effects on the bacteria in the four mesocosms.
-
16N.3.SL.TZ0.12a:
Identify the ecosystem with the appropriate numeral from the climograph.
- 18N.3.HL.TZ0.14b: Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms...
- 19M.3.HL.TZ1.15a: Outline what is represented by the arrows in the Gersmehl diagram.
- 19M.3.HL.TZ2.15a.ii: Using the climograph, identify the relationship between maximum temperature and rainfall.
- 18N.3.SL.TZ0.12b: Calculate how much food would be required to produce 20 kg of boar meat.
- 19M.3.SL.TZ1.10b: Compare and contrast the community structure within and outside the marine protected area.
- 18M.3.SL.TZ2.13a: Identify the processes represented by the arrows labelled A and B in both diagrams.
- 19M.3.HL.TZ2.15a.i: Using the climograph, calculate the range of temperature.
- 16N.3.SL.TZ0.14a: Outline the trend in the number of people with malaria during the period when the use of...
- 19M.3.SL.TZ1.10a: State the trophic level of the sea urchin.
- 17M.3.SL.TZ2.16b: Compare and contrast the biomass in the different trophic levels.
- 18M.3.SL.TZ2.13b: Deduce, with a reason, which ecosystem is representative of a tropical rainforest.
- 17M.3.HL.TZ2.17: Distinguish between tropical rainforest and taiga in terms of nutrient stores, nutrient flows...
-
18M.3.HL.TZ1.15b:
A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.
Predict the process of succession that takes place on exposed bare ground as the glacier retreats.
-
18M.3.SL.TZ1.14a:
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.
-
19N.3.SL.TZ0.12c:
A pyramid of energy represents the amount of energy taken in by each trophic level per unit time and per unit area. Discuss the advantages and disadvantages of the use of pyramids of energy as models of energy flow in an ecosystem.
-
19N.3.HL.TZ0.14b:
Models are used as representations of the real world. Evaluate the use of food webs to represent ecological communities.
- 17M.3.SL.TZ1.14: The Gersmehl diagram below shows the movement and storage of nutrients in a taiga...
- 20N.3.HL.TZ0.17d: A type of ecosystem in Brazil is tropical rainforest. Construct a Gersmehl diagram on the...
- 17M.3.SL.TZ2.17a: State the impact of S. geminata on insect species diversity.
- 18N.3.SL.TZ0.12a: Calculate the increase in mass of a cow given 6 kg of food
- 19M.3.HL.TZ2.15b: Natural forests in the area around Mangalore contain hardwood trees such as teak, Tectona...
- 18N.3.HL.TZ0.14d: Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.
-
19N.3.HL.TZ0.14a:
Feed conversion ratio (FCR) is the mass of animal feed in kilograms required for farmed animals to produce one kilogram of edible mass. For example, the FCR for salmon is 1.2 and for chicken is 2.2. Deduce the implication of these ratios for sustainability.
- 17M.3.SL.TZ2.16c: Outline the reason that parasite biomass occurs in both tertiary consumers and secondary...
- 17M.3.HL.TZ1.13c: Distinguish between mutualism and parasitism, providing another example of mutualism and...
- 18N.3.SL.TZ0.12c: With reference to the data, discuss the farming of salmon for sustainable food production.
- 19M.3.HL.TZ1.15b: Explain how the amount of litter in a tropical rainforest would differ from the taiga’s and...
- 19M.3.SL.TZ2.15: Explain how food conversion ratios in livestock affect the amount of food for human consumption.
- 17N.3.SL.TZ0.12b: Outline why a year is more suitable than a month for the measurement of energy flow.
-
19M.3.HL.TZ2.15c:
The image shows a Gersmehl diagram of tropical rainforest.
[Source: © International Baccalaureate Organization 2019]
Explain what this diagram indicates about nutrients in this type of ecosystem.
-
20N.3.SL.TZ0.15:
Explain what information a pyramid of energy provides about an ecological community.
- 16N.3.SL.TZ0.12b: Referring to the climograph, explain reasons that the nutrient store in the litter layer of...
- 17M.3.SL.TZ2.17b: Discuss whether S. geminata might play a positive role in corn production.
-
18M.3.HL.TZ1.15c:
Compare and contrast food chains and food webs.
- 19N.3.HL.TZ0.16d: Explain how the shape and size of a protected area may influence its success in protecting...
-
20N.3.HL.TZ0.15a:
Outline a method that could have been used in this study to measure the numbers of sea urchins per 0.25 m2.
