Ecosystem Interactions and Population Dynamics

Which of the following is the highest level of organization in this forest environment?

• All the organisms living and interacting together in the environment

• One hawk flying in the sky over the forest

• A group of shrubs in a part of the environment

• A group of one hundred pine trees living closely together in the forest

Answer explanation

The highest level of organization in a forest environment is the ecosystem, which includes all organisms interacting together. The other options represent smaller groups or individual organisms.

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NGSS.MS-LS2-2

Which level of organization does the single fish, Y, represent in the pond environment?

• An organism

• A population

• A community

• An ecosystem

Answer explanation

The single fish, Y, represents an organism because it is an individual living entity. A population refers to a group of the same species, a community includes multiple species, and an ecosystem encompasses all living and non-living components.

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NGSS.MS-LS1-3

Which level of organization do all of the living and nonliving factors, X, interacting in the pond environment represent?

• An ecosystem

• A population

• An organism

• A community

Answer explanation

An ecosystem includes all living (biotic) and nonliving (abiotic) factors interacting in a specific environment, like a pond. Therefore, the correct answer is 'An ecosystem'.

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NGSS.MS-LS2-1

The stingray resting on the bottom of the reef represents —

• an organism, the lowest level of organization in an ecosystem.

• a population, the highest level of organization in an ecosystem.

• a community, the highest level of organization in a community.

• an ecosystem, the lowest level of organization in a community.

Answer explanation

The stingray is a single living entity, making it an organism. Organisms are the basic units of life and represent the lowest level of organization in an ecosystem, unlike populations or communities which involve multiple organisms.

The picture that represents a community is —

• Z, a group of zebra and wildebeests interacting in one environment.

• Y, a single lion resting by itself.

• X, many types of organisms interacting with their nonliving environment interacting.

• W, a group of one type of organisms interacting in one environment.

Answer explanation

Z is correct because it shows a community of different species, zebras and wildebeests, interacting in their environment. This illustrates the concept of a community, unlike the other options which depict solitary or less diverse interactions.

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NGSS.MS-LS2-2

Americans continued to hunt gray wolves during the first half of the 20th century. Which of the following events is least likely to have occurred during this period?

• The population of white-tailed deer increased.

• The population of white-tailed deer disappeared.

• The population of white-tailed deer expanded to new areas.

• The population of white-tailed deer experienced a food shortage.

Answer explanation

The population of white-tailed deer is unlikely to have disappeared during this period, as hunting gray wolves typically leads to an increase in deer populations due to reduced predation, not their complete disappearance.

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NGSS.MS-LS2-1

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When brown tree snakes were accidentally introduced onto the island of Guam, they had no natural predators. These snakes ate many of the eggs of insect-eating birds. What most likely occurred after the brown tree snakes were introduced?

• The insect population increased.

• The bird population increased.

• The insect population sought a new food source.

• The bird population sought a new food source.

Answer explanation

After the introduction of brown tree snakes, the bird population declined due to predation on their eggs. This led to an increase in the insect population, as fewer birds were eating them.

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NGSS.MS-LS2-1

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With scarce resources available in each niche of an ecosystem, what outcome is expected when two species with identical niches compete for resources according to the principle of competitive exclusion?

• One species will outcompete and exclude the other

• Both species will coexist peacefully

• Both species will go extinct

• The resources will become abundant

Answer explanation

According to the principle of competitive exclusion, when two species compete for identical niches, one species will outcompete the other for resources, leading to the exclusion of the less competitive species.

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NGSS.MS-LS2-1

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Which of the following is a biotic and an abiotic factor interacting in this pond environment?

• A. Frog and water

• B. Bird and cattail

• C. Duck and fish

• D. Fish and worm

Answer explanation

A frog is a biotic factor (living organism) and water is an abiotic factor (non-living element). Their interaction in the pond environment exemplifies the relationship between biotic and abiotic components.

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NGSS.MS-LS2-1

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The small bird in this environment interacts with —

• a worm, a biotic factor, as it pulls it up from the ground for food.

• the soil, a biotic factor, as it searches for food inside the soil.

• the tree, an abiotic factor, as it seeks shade under the tree.

• a duck, an abiotic factor, as it competes for food against the duck.

Answer explanation

The correct choice is 'a worm, a biotic factor, as it pulls it up from the ground for food.' This highlights the bird's interaction with a living organism, which is essential for its feeding behavior.

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NGSS.MS-LS2-1

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