Cycling of Matter in an Ecosystem

A scientist studied how nitrogen moves through a grassland ecosystem. He found two different pathways. Use the two models to answer the question.

Where do grassland plants get the nitrogen they need to live and grow?

• from soil

• from plants

• from decomposers

• all of the above

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Which organism gets its energy directly from the Sun?

• frog

• plant

• snake

• cricket

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Which of these accurately represents a food chain?

• sunlight → spider monkey → red cocoa fruit → jaguar

• sunlight → red cocoa fruit → spider monkey → jaguar

• jaguar → sunlight → red coca fruit → spider monkey

• red cocoa fruit → jaguar → spider monkey → sunlight

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Jaden states that animals do not depend on energy from the Sun for food. How would you respond to this statement?

• I would agree with Jaden because animals do not make their own food through photosynthesis.

• I would agree with Jaden because animals eat other organisms to get energy.

• I would disagree with Jaden because animals either eat plants or other animals that eat plants.

• I would disagree with Jaden because animals sun themselves to help keep their bodies warm.

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The corn snake is a secondary consumer that feeds on small mice. The mice eat small seeds from a plant.

Which is the correct order of steps for how a corn snake gets its energy?

• The snake eats the mouse. The seeds are made by a plant. The mouse eats seeds.

• The snake eats the mouse. The plant makes the seeds. The mouse receives energy from the sun.

• The plant makes food from energy received from the sun. The snake eats the mouse. The seeds are made by the snake for the mouse to eat.

• The plant receives energy from the sun. The plant makes the seeds. The mouse eats the seeds. The snake eats the mouse.

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A simple food chain of the pond is shown. Scientists have observed an increase in the fish population in the pond over time. Which changes to the food chain could explain the increase in the number of fish?

• The food source for the fish has increased.

• More people have been fishing in the pond.

• A law was passed to ban fishing in the pond.

• Birds that eat fish have begun nesting at the pond.

• People catch fish from the pond faster than the fish can reproduce.

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What impact do decomposers have on the movement of matter through the ecosystem?

• They make their own food by using energy from the Sun.

• They eat other animals to get their energy they need to survive.

• They survive by eating only the plant matter that uses the Sun to make energy.

• They recycle nutrients into the soil so that other organisms can use them to grow.

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All parts of an ecosystem have a specific role. Match the organism in the ecosystem with the role it has in the ecosystem.

• decomposer

• bacteria

• source of energy for producer

• hawk

• producer

• Sun

• predator

• hare

• prey

• grasses

In 2000, a biologist studied a forest ecosystem and counted the number of plants, rabbits, snakes, and eagles living there. After this, a group of hawks were introduced into the ecosystem. In 2020, the biologist returned and counted the organisms again. The double bar graph shows the results.

What is the best explanation for why the number of eagles in the ecosystem decreased?

• The hawks competed with the eagles for food.

• The hawks hunted the eagles for food.

• The hawks brought pollution, which poisoned the eagles.

• The hawks destroyed the trees where the eagles had lived.

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A student’s aquarium contains rocks, water, Java moss, an earthworm, and two goldfish. Suppose that the student removes the goldfish from the aquarium. What is the best prediction for what will happen to the aquarium?

• The fish are consumers in the ecosystem. If the fish were removed, the water would overflow.

• The fish are producers in the ecosystem. If the fish were removed, the moss would not grow.

• The fish are consumers in the ecosystem. If the fish were removed, the moss would grow larger.

• The fish are producers in the ecosystem. If the fish were removed, the earthworm would not be able to survive.

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