EcologyIB Environmental Systems and Societies SL: Topic test

1. 1
   On rocky shores in Scotland, two barnacle species live in different zones. Chthamalus stellatus lives high on the shore, where it is covered by the sea only at high tide, and Semibalanus balanoides lives lower down. When researchers removed Semibalanus from the lower shore, Chthamalus spread into the lower zone. When Chthamalus was removed from the upper shore, Semibalanus did not colonise the upper zone, and Semibalanus transplanted there died, because it cannot tolerate long exposure to air and drying.

   (a)

   Which interaction between the two barnacle species is shown by the experiment?

   [1 mark]

   • AMutualism
   • BParasitism
   • CCompetition
   • DHerbivory

   (b)

   Which factor limits the distribution of Semibalanus on the upper shore?

   [1 mark]

   • AExposure to air, which dries the barnacles
   • BCompetition from Chthamalus
   • CPredation by dog whelks
   • DDisease

   (c)

   Explain why Chthamalus is found only on the upper shore when both species are present.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   From the 1930s until 1968 a chemical factory released waste containing mercury into Minamata Bay in Japan. Bacteria in the sediment converted some of the mercury into methylmercury, which was taken up by plankton. Mercury is not broken down in living organisms. Shellfish and fish in the bay contained very high concentrations, and people who ate them developed Minamata disease, a serious disorder of the nervous system, which was officially recognised in 1956. Predatory fish contained much higher concentrations than the plankton.

   (a)

   What does it mean to say that mercury is non-biodegradable?

   [1 mark]

   • AIt dissolves quickly in sea water
   • BIt cannot be broken down by living organisms, so it persists in the environment
   • CIt is only harmful to plants
   • DIt is a source of energy for decomposers

   (b)

   Which process describes the increase in the concentration of mercury at each successive trophic level?

   [1 mark]

   • AEutrophication
   • BBioaccumulation within the tissues of a single organism only
   • CSuccession
   • DBiomagnification

   (c)

   Explain why the predatory fish contained much higher concentrations of mercury than the plankton.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A project in the Ethiopian highlands plants native trees on 500 hectares of degraded land. Each hectare of growing woodland absorbs about 5 tonnes of carbon per year. Carbon makes up 12/44 of the mass of carbon dioxide. The project also aims to stop villagers cutting the trees for fuel, because burning wood returns the stored carbon to the atmosphere.

   (a)

   Calculate the mass of carbon dioxide, to the nearest thousand tonnes, that the woodland will absorb over 20 years.

   [3 marks]

   (b)

   Discuss the role of the new woodland as a carbon sink, store and source.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Glacier Bay in Alaska was filled by a huge glacier until about 1750. Since then the ice has retreated by more than 100 km, leaving bare rock, gravel and moraine. Ecologists studied sites that have been free of ice for different lengths of time. Within about 20 years lichens, mosses and mountain avens cover the ground. After about 40 years thickets of alder, which have nitrogen-fixing bacteria in their roots, have formed. After about 80 years Sitka spruce and cottonwood trees grow through the alder. After 150 years or more the site is a forest of spruce and western hemlock. Soil depth and nitrogen content increase with the age of the site.

   (a)

   Explain how changes in environmental conditions allow one community to replace another during this succession.

   [6 marks]

   (b)

   Describe and explain the changes in productivity, species diversity and soil depth during the succession.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   On 19 July 2022 a temperature of 40.3 °C was recorded at Coningsby in Lincolnshire, the highest ever recorded in the United Kingdom. The previous record was 38.7 °C in 2019. The UK Met Office reports that most of the warmest years in the UK since records began in 1884 have occurred in recent decades. Temperate deciduous forest is the natural biome across much of the UK, and ecologists expect the ranges of many species to move as the climate warms.

   (a)

   Which statement best describes climate?

   [1 mark]

   • AThe atmospheric conditions in a place at a particular moment
   • BThe atmospheric conditions in a place on one hot day
   • CThe change in the position of the Sun during a year
   • DThe atmospheric conditions in a place over a relatively long period of time

   (b)

   If the UK continues to warm, which change in biome distribution is most likely?

   [1 mark]

   • ATemperate forest biomes will be replaced by tundra
   • BTemperate forest biomes will shift towards higher latitudes and altitudes
   • CTemperature will no longer affect the distribution of biomes
   • DDeserts will form in northern Scotland

   (c)

   Explain why one record temperature does not by itself show that the climate is changing.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Records of fur sales in Canada over about 90 years show regular cycles of roughly ten years in the numbers of snowshoe hares and Canada lynx. Peaks in lynx numbers follow peaks in hare numbers by a year or two. Hares eat vegetation, and when hare numbers are high the plants are heavily grazed. The lynx feed mainly on hares.

   (a)

   Which statement describes the relationship between the lynx and the hares?

   [1 mark]

   • APredation, in which the lynx is the predator and the hare is the prey
   • BMutualism, in which both species benefit
   • CParasitism, in which the hare lives on the lynx
   • DCompetition, in which both species eat the same plants

   (b)

   Which feedback is shown by the cycles?

   [1 mark]

   • APositive feedback, because the populations grow without limit
   • BPositive feedback, because the lynx cause the hare population to increase
   • CNegative feedback, because rising predator numbers cause prey numbers to fall
   • DNo feedback, because the numbers change at random

   (c)

   Explain why the peak in lynx numbers follows the peak in hare numbers.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A school group wants to estimate the number of daisies in a meadow of 2,000 m². Students used a random number table to place 20 quadrats of 1 m² at random positions. They counted a total of 130 daisies in the 20 quadrats. They noticed that most daisies grew in the drier, sunnier half of the meadow.

   (a)

   Calculate the estimated population of daisies in the meadow.

   [3 marks]

   (b)

   Discuss how reliable the estimate is and how it could be improved.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   In the Southern Ocean, microscopic phytoplankton are eaten by Antarctic krill, which are eaten by Adélie penguins, which are eaten by leopard seals. Krill are also caught commercially for use as feed in fish farms and in omega-3 food supplements, and much of the fishing takes place near breeding colonies of penguins. The fishery is managed by an international commission, which sets catch limits.

   (a)

   Explain why food chains such as this rarely have more than four or five trophic levels.

   [6 marks]

   (b)

   Evaluate the potential effects of a large increase in krill fishing on the Antarctic food web.

   [6 marks]

   Total for question 8: 12 marks

End of questions