An ecosystem is a community of organisms interacting with their physical environment. Why are decomposers an important part of ecosystems?

• They break down dead organisms to return nutrients to the soil.

• They produce their own food for survival.

• They play a role in preventing weathering and erosion.

• They provide most of the energy to consumers.

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The diagram above shows part of a river food web. Which change would MOST likely reduce the number of both large roach fish and steelhead fish?

• an increase in the amount of algae

• an increase in the number of small invertebrates

• a decrease in the number of predatory invertebrates

• a decrease in the number of young stickleback fish

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The diagram above shows part of an ocean food web.

Which effect will an increase in sea urchins MOST likely have on this food web?

• a decrease in the number of sea otters

• a decrease in the amount of seaweed

• a decrease in the amount of sunlight

• a decrease in the number of parrotfish

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The diagram above shows a marine food web. Changing ocean temperatures have led to a large decrease in the number of horseshoe crabs. Which effect will MOST likely occur next?

• The diamondback turtle and grackle populations will decrease.

• The striped bass and plankton populations will decrease.

• The razor clam population will increase.

• The sanderling population will increase.

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Noah visited a park that had many oak trees. Which BEST describes the role of an oak tree in its ecosystem?

• Oak trees can live for a long time.

• Oak trees have leaves that change colors.

• Oak trees have strong branches and trunks.

• Oak trees are a source of food and shelter for animals.

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A brown bear eats a variety of foods including berries, insects, and small animals. Which BEST describes a brown bear?

• producer

• herbivore

• carnivore

• omnivore

Farmers plant fruit trees in an area that was once a grassy meadow. Which will MOST likely happen to the rabbits living in the meadow?

• They will learn to eat fruit.

• They will learn to climb trees.

• The number of their young will increase.

• The size of their population will decrease.

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Numbers of Florida scrub jays have recently been decreasing throughout Florida. Which is the MOST likely reason for smaller populations of Florida Scrub Jays?

• habitat loss

• fewer predators

• more eggs hatching

• new food sources available

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Wood ducks build their nests in holes in trees near lakes. If some of the trees were removed from around the lake, how would the wood ducks be affected?

• Wood ducks would become a new species.

• Wood ducks would lay more eggs in each nest.

• Wood ducks would increase their competition for nests.

• Wood ducks would begin building their nests on the ground.

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Decaying plants and animals are important to an ecosystem because they

• cause disease in living organisms.

• reduce soil erosion.

• recycle oxygen to the air.

• return nutrients to the soil.

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