Matter and Energy in the Ecosystem

Which statement describes the role of decomposers in a food web?

• Decomposers are not necessary in a food web.

• Decomposers break down matter so plants can use it.

• Decomposers create energy by producing their own food.

• Decomposers store matter and energy until it is needed in an ecosystem.

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Producers and consumers are both pictured in a diagram of a food web. Which statement best describes how they differ from one another?

• Consumers produce all the energy they need.

• Consumers eat only animals, and producers eat only plants.

• Producers eat living organisms, and consumers eat organisms that have died.

• Consumers obtain energy by eating food, and producers obtain energy from sunlight.

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What is the primary role of decomposers in a food web?

• to control the population of producers and consumers

• to compete with producers for energy and other resources

• to provide a source of energy for the producers in the ecosystem

• to recycle energy and materials from dead producers and consumers

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Different grasses are observed in a microhabitat in a schoolyard. Why is grass an essential part of a healthy ecosystem?

• It is a producer that is a necessary part of the diet of most consumers.

• It is a consumer that feeds off other organisms living in the area.

• It is a decomposer that converts matter into a form that other organisms can use.

• It makes up the last level of a food web, helping recycle carbon in the habitat.

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A student is identifying food chains in a diagram of a food web. Which of these organisms might be a consumer?

• a frog

• a water lily

• a redwood tree

• athlete's foot fungus

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A mangrove swamp contains many organisms living among the large roots of the mangrove trees. The food web shows some of the relationships in that ecosystem. According to the food web, which of these organisms is a producer in the mangrove swamp?

• mold

• prawn

• pelican

• phytoplankton

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NGSS.MS-LS2-3

The figure shows a food chain that might exist in a meadow. If there was a decrease in the beetle population, how might the food chain be affected?

• The owl population would decrease.

• The population of green plants would decrease.

• The toad and snake populations would increase.

• The green plants and toad populations would decrease.

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Ants eat a variety of foods, including plants and other insects. A reptile called a thorny devil eats ants. If a food chain that includes the thorny devil and ants is represented by an energy pyramid, the ants would occupy the ___________ pyramid level.

• top

• middle

• bottom

Answer explanation

Only producers can occupy the bottom level of an energy pyramid. Since ants are prey for thorny devils, they cannot occupy the top level of the pyramid.

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NGSS.MS-LS2-3

Ants eat a variety of foods, including plants and other insects. A reptile called a thorny devil eats ants, drinks water, and breathes in air to get oxygen. Which statement about thorny devils and ants is true?

• The thorny devil stores almost all of the energy it receives from eating ants.

• Thorny devils get all the matter they need from eating ants.

• There is likely an equal number of ants and thorny devils in the desert ecosystem.

• Carbon and other nonliving materials flow from ants to thorny devils as ants are eaten.

Answer explanation

An organism stores about 10% of the energy it obtains from food and uses the rest for life processes. Given their large size, thorny devils must consume many ants each day. The ratio of ants to thorny devils needs to be large, not 1:1. Thorny devils need water and air in addition to the matter they get from eating ants.

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NGSS.MS-LS2-3

Which statement(s) describe how the river moves matter between land and water ecosystems? Select two (2) that apply.

• The river provides water to many land animals.

• The river draws soil nutrients into the water for use by aquatic plants.

• The pull of gravity allows water to move from where it falls as rain, returning it to the ocean.

• Rivers carry rocks downstream.

Answer explanation

Matter is transferred from the aquatic ecosystem to the land ecosystem when animals drink from the river. Matter is transferred from the land ecosystem to the aquatic ecosystem when soil enters the river.

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