Mod C Unit 3 Lesson 2 Changes in Ecosystems

Some grass species need fire in order for their seeds to germinate. Why might this adaptation be useful for grasses?

• Fire allows trees to grow and to provide shade for the grasses.

• The hot temperature of the fire helps the grasses grow faster.

• Seeds can germinate in an area that has been cleared by a fire.

• Fire discourages grazing by large animals so the grasses can grow higher.

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How can you tell from the diagram that this is an example of secondary succession rather than of primary succession?

• No plants exist when the process begins.

• Soil is present at the beginning of the process.

• The process ends with the growth of large trees.

• The sizes of the plants generally increase over time.

Which statement best describes ecosystems?

• They can never change once they are established.

• They constantly change in different ways over time.

• Ecosystems always revert back to their original state.

• Each ecosystem can exist for only a specific length of time.

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Which of these might result from the process of natural eutrophication?

• A pond becomes a meadow.

• A rock breaks down into soil.

• A glacier retreats to expose new land.

• A nonnative species takes resources from native species.

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The table lists the number and variety of organisms in four different ecosystems. Predict what would happen to Ecosystem 3 immediately after a volcanic eruption.

• Its biodiversity would decrease.

• Its biodiversity would not change.

• The number and variety of organisms in the ecosystem would be greater than those in Ecosystem 1.

• The number and variety of organisms in the ecosystem would be greater than those in Ecosystem 2.

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How is secondary succession different from primary succession?

• Secondary succession occurs over a longer period of time than primary succession.

• Secondary succession occurs when animals are introduced to an area that had only plants.

• Secondary succession occurs after a disturbance in an area that was previously uninhabited.

• Secondary succession occurs after a disturbance in an area in which the soil has remained intact.

What is the first step in the eutrophication of a pond?

• A meadow develops.

• Plant communities take over.

• Excess nutrients build up in the water.

• Debris builds up on the bottom of the pond.

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A lahar is a mudflow made up of lava, water, and rocks. How might a lahar affect an ecosystem?

• It is a sudden disturbance that affects few populations in the affected area.

• It is a sudden disruption that affects all local populations in the affected area.

• It is a gradual disruption that affects only animal populations in the affected area.

• It is a sudden disruption that has little effect on plant populations in the affected area.

Answer explanation

A lahar happens quickly and can cover large areas of an ecosystem.

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When Mt. St. Helens erupted, the resulting lahar flowed over a wide area of the Cascade Mountains. Which statements best describe the effect of the volcanic eruption? Select three (3) that apply.

• It affected the living and nonliving components of the ecosystem.

• It removed populations of mammals from the mountainside.

• It led to succession on the mountainside.

• It affected only nonliving components of the ecosystem.

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An event that causes changes to the living and nonliving parts of an ecosystem is called a _______________.

• biodiversity hotspot

• disturbance

• sudden change

• catastrophic event

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