UNIT 7 REVIEW

An ecosystem that is not sustainable can break down when a natural disaster occurs. This can lead to organisms in the ecosystem either leaving the area or dying off.

Increased biodiversity results in a more sustainable ecosystem because -

• a greater number of plant species means that there is less barren land

• a greater variety of species present

  allows more organisms to adapt after

  changes occur

• the transition area between two

  ecosystems is narrower

• there are fewer species to be

  affected by environmental stress

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Students in a science class visited four local ecosystems. The students observed the species present in each ecosystem and recorded their observations in the table.

Based on these observations, which ecosystem is likely to be the least sustainable?

• Ecosystem 1, because it has the fewest species.

• Ecosystem 2, because it includes both aquatic and terrestrial species.

• Ecosystem 3, because it has few predators.

• Ecosystem 4, because it supports many animals.

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Tropical rain forests have the greatest biodiversity of any type of land ecosystem. How does biodiversity contribute to the sustainability of an ecosystem?

• The presence of more species with different adaptations makes it more likely that some organisms will survive

  an ecological disaster.

• Greater genetic variation within

  species makes it more likely that some

  individuals will survive a disease

  outbreak.

• The presence of a variety of

  herbivore species that can feed on a large number of different producer species help ensure abundant prey for predators in the ecosystem.

• All of the above.

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

Which ecosystem would be more likely to survive if a disease killed the grasses?

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

• The grassland ecosystem, because several predators compete for food.

• The forest ecosystem, because it has three top predators.

• The grassland ecosystem, because it has many herbivores.

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Primary succession occurs when pioneer species move into an area that has no plants. Which organisms are common pioneer species?

• Conifer trees and tall grasses with roots that loosen the soil.

• Mosses and lichens that can grow on rocky surfaces.

• Grasses and weeds that arrive as

  seeds carried by the wind and then

  germinate in rich soil.

• Vines and shrubs that help prevent the erosion of shallow soil.

Both primary and secondary succession begin with pioneer species that -

• change the area and make it safer

  from predatory organisms.

• invade the area so that new

  organisms cannot be established.

• modify the area and allow larger and more complex organisms to appear.

• use up all the existing resources and prevent establishment of non-native

  organisms.

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Some students take care of a vegetable garden. When it is time to plant in the spring, the students leave part of the garden empty in order to observe ecological succession. Which of these will most likely occur first?

• Development of topsoil

• Growth of weeds and grasses

• Growth of trees and shrubs

• Development of a stream

The final stable community that is made up of mature, hardwood trees is called-

• Pioneer community

• Climax community

• Farmland

• Old field

A pioneer species such as ________ are a combination of algae and fungus that grow on bare rock.

• Lichens

• Mistletoe

• Legumes

• Mushrooms

A hurricane hits a coastal prairie and destroys that habitat. Years later there is an appearance of small plants with rapidly spreading roots. This vegetation describes-

• A microhabitat

• Primary succession

• Secondary succession

• Biodiversity

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