Food Chains, Webs, and Pyramids

The best explanation for the decrease in the amount of energy available as one moves up the pyramid is that

• producers require more energy than consumers to survive

• decomposers recycle nutrients at each level

• much of the energy at each level is lost as heat

• animals use less energy than plants

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Kelp forest ecosystems are primarily located in the Pacifi c Ocean off the coasts of California and Alaska. The increased demand for sea urchins, whose roe (a mass of eggs) is a Japanese sushi ingredient, is causing them to be overharvested. A team of students is concerned that this decrease might affect the number of other organisms inhabiting a kelp forest ecosystem. The students studied the feeding relationships in the ecosystem and constructed the food web.

Describe one role of the sea urchin population in the kelp forest ecosystem

• They are herbivores and eat the Kelp

• They are prey for the Sea Otters

• They are prey for Sea Stars

• All of the above

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All choices describe one way a decrease in the number of sea urchins would affect the population of large fish except choice

• The number of large fish would most likely decrease because sea otters would eat more of them.

• It might not affect the large fish population, because their diet doesn’t consist of sea urchins or the organisms that depend on sea urchins.

• It might decrease because there would be more kelp for the large crabs to eat.

• The population of large fish would decrease. Sea otters would consume more large crabs, which serve as food for the large fish.

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Another team of students predicted that, if they removed all of the sea stars, the ecosystem might remain stable. which explanation would not prove why removing sea stars might seem like a good way to make up for the overharvesting of the sea urchins

• The sea urchins now have many predators, so the population may increase/remain stable.

• The sea urchins now only have one predator, so the population may increase/remain stable.

• Only fishing and sea otters would be removing sea urchins, not predatory sea stars, so the ecosystem would remain stable.

• The sea stars eat sea urchins. With the sea stars gone, the remaining sea urchins will not be eaten by sea stars.

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Why removing the sea stars from the food web could result in the loss of the entire kelp ecosystem? (Choose all that apply)

• The kelp ecosystem would be destroyed. Snails would increase out of control since the only animal eating them was the sea stars.

• The snails and sea urchins would consume the kelp.

• The sea otters would be feeding more on large crabs since there are no sea stars. Soon, sea otters would run out of food.

• If sea stars are removed, the organisms in the other populations present will be affected. All of these populations are linked either directly or indirectly. With the sea stars gone and a reduced number of sea urchins, the ecosystem will be out of balance and likely disappear.

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Which row in the chart correctly pairs a group of organisms with the type of nutrition they carry out?

• 1

• 2

• 3

• 4

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Which diagram below best represents the direction that energy flows through an energy pyramid?

• 
• 
• 
• 

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Based on the food web, the population that contains the greatest amount of available energy would be

• seals

• fishes

• phytoplankton

• humans

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Which statement best describes what would happen in this ecosystem if the phytoplankton were removed from the food web?

• Copepods and krill would fi ll the vacant niche.

• The number of heterotrophs would increase.

• The food web would be disrupted, and organisms would die.

• The food web would remain stable.

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Describe the relationship represented by the arrows between squids and fishes.

• Fish can be predators of squid, and squid can be predators of fish.

• Each species can be both predator and prey.

• They can feed on each other.

• No choices are correct

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