Ecosystems 2525

A population of rabbits in a grassland suddenly decreases due to disease. Predict how this change might affect the populations of grass and foxes in the same ecosystem over time.

• Grass population will decrease, and fox population will increase.

• Grass population will increase, and fox population will decrease.

• Both grass and fox populations will increase.

• Both grass and fox populations will decrease.

Answer explanation

With the rabbit population declining, there will be less grazing pressure on grass, allowing its population to increase. Conversely, fewer rabbits mean less food for foxes, leading to a decrease in their population.

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Plants capture the sun's energy and transfer that energy into chemical energy stored in the bonds of a sugar in a process called photosynthesis. What happens to the sugars?

• They are used for energy.

• They are used for growth and maintenance.

• They are stored for energy or used for growth and maintenance.

• They are lost as heat, stored for energy, or used for growth and maintenance.

Answer explanation

The correct choice states that sugars can be lost as heat, stored for energy, or used for growth and maintenance. This reflects the various fates of sugars produced during photosynthesis in plants.

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In the energy pyramid here, how much of the energy in the producers gets passed to the herbivores?

• 10%

• 20%

• 80%

• 90%

Answer explanation

In an energy pyramid, typically only about 10% of the energy from producers is transferred to herbivores. This is due to energy loss at each trophic level, primarily through metabolic processes and heat.

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Given a food web with the following organisms: grass, grasshopper, frog, snake, and hawk, what would likely happen if all the frogs were removed?

• Grasshopper population would decrease, and snake population would increase.

• Grasshopper population would increase, and snake population would decrease.

• Grasshopper and snake populations would both increase.

• Grasshopper and snake populations would both decrease.

Answer explanation

Removing frogs eliminates a predator of grasshoppers, allowing their population to increase. With more grasshoppers, snakes, which prey on them, may find less food, leading to a decrease in their population.

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Suppose a pesticide is used to eliminate insects in a crop field. Predict the possible effects on both the plants and the birds that feed on these insects.

• Plant population will decrease, and bird population will increase.

• Plant population will increase, and bird population will decrease.

• Both plant and bird populations will decrease.

• Both plant and bird populations will increase.

Answer explanation

The pesticide reduces insect populations, leading to less food for birds, which may cause their population to decrease. Meanwhile, with fewer insects damaging them, plants can thrive, resulting in an increase in plant population.

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Glucose is a simple sugar that is classified as a carbohydrate. Which best explains how organisms get carbohydrates to obtain the energy that they need?

• Producers and consumers use sunlight, carbon dioxide, and water to produce carbohydrates.

• Heterotrophs produce carbohydrates.

• Autotrophs produce carbohydrates.

• Plants and animals produce carbohydrates from cell respiration.

Answer explanation

Autotrophs, like plants, produce carbohydrates through photosynthesis, using sunlight, carbon dioxide, and water. This process is essential for creating the energy-rich compounds that organisms need.

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A river ecosystem contains algae, small fish, large fish, and eagles. If pollution kills most of the small fish, what is the most likely effect on the algae and eagle populations?

• Algae population will decrease, and eagle population will increase.

• Algae population will increase, and eagle population will decrease.

• Both algae and eagle populations will increase.

• Both algae and eagle populations will decrease.

Answer explanation

With the small fish gone, algae will thrive due to reduced grazing pressure, leading to an increase in their population. Eagles, relying on small fish as a food source, will likely decrease in number due to food scarcity.

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In a food web, rabbits eat grass, and foxes eat rabbits. If humans introduce a new plant that outcompetes grass, what could be the long-term effect on the rabbit and fox populations?

• Both rabbit and fox populations will increase.

• Rabbit population will decrease, and fox population will decrease.

• Rabbit population will increase, and fox population will decrease.

• Rabbit population will decrease, and fox population will increase.

Answer explanation

The introduction of a new plant that outcompetes grass will lead to a decrease in rabbit populations due to lack of food. Consequently, with fewer rabbits, fox populations will also decline due to reduced prey availability.

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Which of the following would be best classified as a primary consumer?

• the ladybug that eats beetles

• the cricket that eats flowers

• the mouse that eats grasshoppers, caterpillers, beetles, and grubs

• the sunflower that converts the solar energy into chemical energy

Answer explanation

The cricket that eats flowers is a primary consumer because it directly consumes producers (plants). The other options either consume other consumers or are producers themselves.

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A marine food web includes phytoplankton, zooplankton, small fish, and sharks. If overfishing removes most of the small fish, what is the most likely impact on the zooplankton and shark populations?

• Zooplankton population will decrease, and shark population will increase.

• Zooplankton population will increase, and shark population will decrease.

• Both zooplankton and shark populations will increase.

• Both zooplankton and shark populations will decrease.

Answer explanation

Removing small fish reduces their predation on zooplankton, allowing zooplankton populations to increase. With fewer small fish available as prey, sharks will have less food, leading to a decrease in their population.

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