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Which statement best describes an ecosystem maintaining a state of approximate equilibrium?*
The chart below represents some of the events
that occur during the cycling of nutrients in an ecosystem.
Which organisms would most appropriately complete the chart when written in the circle at X?*
Which group of organisms in an ecosystem fills the niche of recycling organic matter back to the environment?*
Base your answers to questions 4 on the diagram below and on your knowledge of biology. The diagram represents interactions between organisms in an ecosystem.
Which statement correctly describes an interaction that contributes to the stability of this ecosystem?*
The diagram below does not represent a sustainable energy pyramid in an ecosystem because
Base your answers to questions 6 on the diagram below and on your knowledge of biology. The diagram represents various levels of interaction between organisms in a prairie ecosystem.
If the amount of carbon dioxide in the atmosphere were to decrease, which organism in the diagram would be one of the first affected by this change?*
Four levels of an energy pyramid are represented below.
Which statement about this energy pyramid is correct?*
Carbon dioxide and oxygen are important resources in ecosystems and are*
Which type of organism helps to reduce atmospheric carbon dioxide?*
Which level of the pyramid below is correctly paired with the type of organism that would most likely be found at that level in an ecosystem?
Base your answer to question 11-14 on the diagram below and on your knowledge of biology. The diagram represents three groups of organisms that are part of an ecosystem.
Explain the role of these groups of organisms in the cycling of materials and the transfer of energy in an ecosystem. In your answer, be sure to:
• explain why an ecosystem requires a constant input of energy 
• explain how organisms in group B obtain energy 
• explain the role of organisms in group C in the ecosystem 
• identify the process used by all three groups of organisms to make energy available to their cells to carry out life functions *
Base your answers to questions 15 on the diagram below and on your knowledge of biology. The diagram represents the energy in kilocalories (kcal) available at different feeding levels in a food chain.
Explain why there is a different amount of energy represented at each level of this energy pyramid. *
People who live in rural areas often use septic tanks for the storage of sewage. These people often flush a product containing harmless bacteria down the toilet once a month. These bacteria break down the sewage before it enters the environment. State one ecologically sound reason for this action. *
Base your answers to questions 17 on the diagram below and on your knowledge of biology. The diagram represents trophic levels in an ocean environment.
State one reason why there is less energy available at each trophic level going from the first to the third trophic level. *
Base your answers to questions 18 on the information and passage below and on your knowledge of biology.
Snowy Owls Move to the South
Snowy owls are large white birds that normally inhabit the cold northern regions of Canada. Recently, scientists and birdwatchers have sighted the snowy owls much farther south than usual.
When snowy owls are in northern areas, they feed on lemmings (small rodents). When lemmings are not available, as in the areas further south, the owls will seek out mice or rabbits as their food source.
Several snowy owls migrated into an area represented by the food web below.
State which level, A, B, or C, contains the least total available energy. Support your answer.