Unit 7 Organisms and their Ecosystems

Students created the table below based on observations of two microhabitats near their school.

Based on the information above, what is the best explanation for the different variety of organisms in the two microhabitats?

• The rotting log and grassy area are in different biomes.

• Conditions for survival are different in each location.

• The rotting log has predators while the grassy area does not.

• There is more space in the rotting log than in the grassy area.

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The more diverse an ecosystem is --

• the more threatened its populations are

• the more similar the species will be

• the more sustainable it is

• the fewer varieties of species are present

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Refer to the food webs above. If the grasses in each ecosystem are attacked or killed by a disease, which ecosystem will most likely survive?

• The prairie ecosystem, because fewer organisms eat grass

• The tundra ecosystem, because there is a variety of producers

• The prairie ecosystem, because there are fewer top predators

• The tundra ecosystem, because it has more herbivores

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Which statement below best describes how biodiversity contributes to the sustainability of an ecosystem?

• A variety of plant and animal species allows for more survivors of a natural disaster.

• Having more species in an ecosystem allows the human population to increase in size.

• Low biodiversity reduces the competition for resources, which helps native species survive.

• Fewer species in the ecosystem reduces the likelihood that disease spreads through the ecosystem.

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Which of the following situations contributes to the sustainability of an ecosystem?

• Increase in biodiversity

• Decrease in biodiversity

• Extinction of a population from the ecosystem

• Removal of many populations of organisms

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The food webs below model relationships among organisms in two ecosystems.

Students were asked to make a claim supported with evidence to answer the question, “Which ecosystem would be most sustainable if all the grasses died from severe drought?” What claim is valid and supported by the evidence?

• The forest ecosystem is most sustainable because there are more top predators.

• The grassland ecosystem is most sustainable because there are fewer organisms that eat grass.

• The forest ecosystem is most sustainable because most of the animals can eat other organisms.

• The grassland ecosystem is most sustainable because there is less competition for food.

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Which event would most likely cause an ecosystem to have the lowest biodiversity and population sizes 3 years later?

• Clearing land for a highway

• A river floods a cornfield

• A forest fire destroys the plant growth

• A lava flow creates a new section of land

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The role of a pioneer species in primary succession is to change a bare habitat into one that is suitable for other organisms. A species that is responsible for primary succession in an ecosystem is most likely able to —

• survive any predator

• migrate during the winter

• live at high altitudes

• carry out photosynthesis

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Which of the following sequences most likely represents ecological succession on a recently abandoned wheat field?

• grasses → flowering plants → shrubs → native trees

• native trees → shrubs → flowering plants → grasses

• shrubs → grasses → native trees → flowering plants

• flowering plants → native trees → shrubs → grasses

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What is the relationship between ecological succession and equilibrium in an ecosystem?

• Ecological succession leads to equilibrium in an ecosystem.

• Ecological succession prevents ecosystems from ever reachingequilibrium.

• There is no relationship between ecological succession and equilibrium.

• Ecological succession and equilibrium are the same thing.