Ecology
Past Paper Questions
1. Outline what is meant by the
trophic level of an organism with
three examples from one named
habitat. 4 marks
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
2. Compare the way in which
autotrophic, heterotrophic and
saprotrophic organisms obtain
energy. 5 marks
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
3. Explain reasons for the shape of
pyramids of energy. 3 marks
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
5 . Explain that energy enters and
leaves ecosystems, but nutrients must
be recycled. 5 marks
5. Explain that energy enters and leaves ecosystems,
but nutrients must be recycled. 5 marks
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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
5. Draw and label a diagram of the
carbon cycle to show the process
involved. 4 marks
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
6. Explain the relationship between
rises in concentrations of atmospheric
carbon dioxide, methane and oxides
of nitrogen and the enhanced
greenhouse effect. 8 marks
6. Explain the relationship between rises in
concentrations of atmospheric carbon dioxide,
methane and oxides of nitrogen and the enhanced
greenhouse effect. 8 marks
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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)
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
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
8. Outline the consequences of a
global temperature rise on arctic
ecosystems. 3 marks
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