2.2 Energy and biomass in ecosystemsIB Environmental Systems and Societies HL: Subtopic test

1. 1
   In the 1950s and 1960s the insecticide DDT was sprayed widely to control insects. DDT does not break down easily and is absorbed by organisms. Studies of a lake food chain found very low concentrations of DDT in the water, higher concentrations in plankton and small fish, and the highest concentrations in fish-eating birds, whose eggshells became thin and cracked.

   (a)

   What is the term for the increase in the concentration of a pollutant at each successive trophic level?

   [1 mark]

   • ABioaccumulation
   • BEutrophication
   • CBiomagnification
   • DBiodegradation

   (b)

   Which of the following is also a non-biodegradable pollutant that biomagnifies?

   [1 mark]

   • AMercury
   • BCarbon dioxide
   • CNitrate
   • DSucrose

   (c)

   Explain why the concentration of DDT was highest in the fish-eating birds.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   At hydrothermal vents on the floor of the Pacific Ocean, more than 2000 m down, no sunlight reaches the seabed. Even so, dense communities live around the vents, including giant tube worms (Riftia pachyptila). The tube worms have no mouth or gut and house bacteria that use energy from the oxidation of hydrogen sulphide in the vent fluid to make carbon compounds from carbon dioxide.

   (a)

   What type of organism are the bacteria living in the tube worms?

   [1 mark]

   • APhotoautotrophs
   • BHeterotrophs
   • CDecomposers
   • DChemoautotrophs

   (b)

   What is the external energy source for the producers at the vents?

   [1 mark]

   • ASunlight absorbed by chlorophyll
   • BExothermic inorganic chemical reactions
   • CGlucose from the surface waters
   • DHeat from cellular respiration

   (c)

   Distinguish between photoautotrophs and chemoautotrophs.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Researchers measured the energy flow in a grassland ecosystem over one year. Net primary productivity of the producers was 8000 kJ m⁻² yr⁻¹. The primary consumers gained 960 kJ m⁻² yr⁻¹ in biomass and the secondary consumers gained 120 kJ m⁻² yr⁻¹. The tertiary consumers gained 15 kJ m⁻² yr⁻¹.

   (a)

   Calculate the ecological efficiency of the transfer from the producers to the primary consumers and explain what happens to the energy that is not transferred.

   [3 marks]

   (b)

   Using the data, explain why food chains usually have no more than four or five trophic levels and why sustainable yields are higher at lower trophic levels.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In the Brazilian state of Mato Grosso large areas of tropical forest and savanna have been cleared since the 1990s. Much of the land is now cattle pasture or soya bean fields, with soya mostly grown to feed livestock and for export. Some of the forest was burned to clear the land.

   (a)

   Explain how human activities such as these affect the flows of energy and the transfers of matter in ecosystems.

   [6 marks]

   (b)

   Evaluate the sustainability of converting tropical forest to cattle pasture, using ideas about productivity and trophic levels.

   [6 marks]

   Total for question 4: 12 marks

End of questions