Ecology

1. Ecology Past Paper Questions

2. 1. Outline what is meant by the trophic level of an organism with three examples from one named habitat.4 marks

3. 1. Outline what is meant by the trophic level of an organism with three examples from one named habitat.4 marks • definition: feeding level for an organism in a food chain • naming of habitat • naming three trophic levels correctly • three examples forming a food chain from the named habitat

4. 2. Compare the way in which autotrophic, heterotrophic and saprotrophic organisms obtain energy.5 marks

5. 2. Compare the way in which autotrophic, heterotrophic and saprotrophic organisms obtain energy.5 marks • autotrophs use an external / non-organic energy source • (reject statements suggestion that energy is made) • (some) autotrophs use light / (some) autotrophs use photosynthesis • (some) autotrophs use inorganic chemical reactions / (some) autotrophs use chemosynthesis • heterotrophs obtain energy from other organisms • heterotrophs (usually) ingest food / consume food • saprotrophs obtain energy from non-living matter / dead organisms • saprotrophs digest organic matter extracellularly

6. 3. Explain reasons for the shape of pyramids of energy.3 marks

7. 3. Explain reasons for the shape of pyramids of energy.3 marks • energy pyramids illustrate the quantity of energy within the biomass of each trophic level • only a portion / 10-20% of energy in any level is transferred to the next • some (50%) energy is not assimilated / lost as feces (indigestible cellulose) • some (40%) energy is lost as heat during cellular respiration • remaining (10%) energy is incorporated into biomass

8. 5 . Explain that energy enters and leaves ecosystems, but nutrients must be recycled.5 marks

9. 5. Explain that energy enters and leaves ecosystems, but nutrients must be recycled.5 marks • max 3 marks for each of energy and nutrients • Energy • Earth constantly loses incoming energy by reflection and radiation • producers consume only about 1% of solar energy during photosynthesis • each conversion between trophic levels loses 90% of energy as heat / by cellular respiration • total energy entering an ecosystem equals the total energy lost to the environment • Nutrients • Earth does not exchange significant amounts of matter with space • total quantity of matter on Earth is static • ecosystems recycle their nutrients • producers absorb inorganic nutrients from their environment • consumers use the nutrients gained from the organisms they eat • decomposers break down nutrients from dead / decaying organisms • recycling requires energy

10. 5. Draw and label a diagram of the carbon cycle to show the process involved.4 marks

11. 5. Draw and label a diagram of the carbon cycle to show the process involved.4 marks • award one mark for each aspect of the carbon cycle accurately representing each of: • atmosphere as reservoir of carbon dioxide gas • photosynthesis: carbon dioxide from atmosphere to producer • cell respiration: loss of carbon dioxide from organisms to atmosphere • fossilization: burying of organic matter releasing carbon dioxide to atmosphere • combustion: burning of fossil fuels / organic matter releasing carbon dioxide to atmosphere • sedimentation: carbon deposits as rock • volcanoes: releasing carbon dioxide to atmosphere

12. 6. Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.8 marks

13. 6. Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.8 marks • the greenhouse effect is a natural phenomenon • transmission of incoming shorter-wave radiation through atmospheric gasses • greenhouse gases cause enhanced greenhouse effect by reflecting long wave radiation back to Earth • carbon dioxide added to atmosphere by fossil fuel combustion • carbon dioxide added to atmosphere by rain forest clearing & combustion • methane added to atmosphere by agriculture / rice paddy / methanogen bacteria • methane added to atmosphere by intestinal methanogen bacteria in livestock • nitrogen oxides / ozone added to atmosphere by fossil fuel combustion • chlorofluorocarbons added to atmosphere by refrigerants / coolants / air conditioners / cleaning solvents / aerosols and propellents • enhanced greenhouse effect causes global increase in lower atmosphere temperature of 1.5 - 4.5 °C / 50 years • enhanced greenhouse effect causes agricultural disruption / changing weather patterns / ecosystem disruption • enhanced greenhouse effect causes polar ice cap melting leading to coastal flooding • enhanced greenhouse effect causes spread of tropical diseases (e.g. malaria)

14. 7. Define the precautionary principle and evaluate it as a justification for strong action in response to the threats posed by the enhanced greenhouse effect.4 marks

15. 7. Define the precautionary principle and evaluate it as a justification for strong action in response to the threats posed by the enhanced greenhouse effect.4 marks • definition: if the effects of a human-induced change would be very large, those responsible for the change must prove that it will not do harm before proceeding • if consequences of global warming are devastating preventive measure are justified, even without certainty about global warming cause and effects • balance economic harm of limiting measures taken currently versus greater harm in future by taking no action • ethical question: should welfare of future human generations be jeopardized • ethical question: is it right to knowingly damage habitats of, and possibly drive to extinction, species other than humans? • only through international cooperation can a solution be found • inequality between those most responsible for the problem and those most harmed

16. 8. Outline the consequences of a global temperature rise on arctic ecosystems.3 marks

17. 8. Outline the consequences of a global temperature rise on arctic ecosystems.3 marks • increased rates of decomposition of detritus previously trapped in permafrost • expansion of the range of habitats available to temperate species • loss of ice habitat • changes in distribution of prey species affecting higher trophic levels • increased success of pest species, including pathogens