Ecosystem Interactions

Wild hogs introduced to Texas from Europe became feral after the hogs escaped from the ranches where they lived. Feral hogs are omnivores that feed on native plants, crops, and small animals. Feral hogs can damage an ecosystem by rooting through the soil to look for food and trampling small plants.

Which types of native organisms do feral hogs most likely compete with for food sources?

• Carnivores and producers

• Herbivores and carnivores

• Producers and decomposers

• Decomposers and herbivores

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Giant salvinia is an aquatic plant that floats on water and reproduces rapidly. When these plants die, decomposition by bacteria affects oxygen levels in the water. As more plants die, less oxygen is available in the water. Students observe a pond covered by giant salvinia.

Which statement is the best prediction the students can make about the immediate future of the pond?

• The depth of the water in the pond will increase.

• Fish populations in the pond will begin to decrease.

• The amount of bacteria in the pond will suddenly decrease.

• The number of different types of plants around the pond will increase.

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Plants grow in many different shapes and sizes. Much of their shape depends on an internal structure that is composed of carbon-containing molecules such as cellulose and lignin. Plants that have a strong internal structure can grow larger than other plants because their structure can support their size.

Plants obtain the majority of the carbon necessary for building these structural molecules from —

• air

• microorganisms

• soil

• water

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A group of scientists studied some trees in a pine forest. In the densely forested areas, the trees were within 1 m of each other. The scientists observed that these trees had dead branches near the ground. They measured the height above the ground at which the first living branches were found on different-sized trees in the forest. Then they repeated this procedure on the same kind of trees in an open meadow. This graph summarizes the scientists’ data.

Which inference is best supported by these data?

• Pine trees in a dense forest can grow taller than pine trees in an open meadow.

• Pine trees in a dense forest compete for sunlight with the surrounding trees.

• Pine trees in a dense forest are part of a less-complex food web than pine trees in an open meadow.

• Pine trees in a dense forest have more living branches than pine trees in an open meadow.

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Whitetip reef sharks spend most of the day lying on the ocean floor. While remaining still, these sharks pump water across their gills.

The movement of water across their gills is necessary for —

• staying cool

• accessing food

• obtaining oxygen

• avoiding predators

A scientist added bacteria and a nutrient medium that could support the growth of the bacteria to a sterilized petri dish. No other materials were added. The graph models growth of the bacteria over time.

Which of these most likely explains why the bacterial population stopped growing?

• The bacteria competed for nutrients and died after all the nutrients were consumed.

• The bacteria did not reproduce in the system, and eventually each individual died at the end of its life cycle.

• The bacteria mutated from photosynthetic to carnivorous organisms and consumed one another until all the individuals were dead.

• The bacteria became diseased and were unable to survive in the closed system.

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The strangler fig is a vine that starts out as a seed in the tree canopy of the rain forest. It drops its roots down from the canopy to the forest floor.

By sprouting in the rain-forest canopy, the strangler fig seedling is exposed to more

• sunlight

• soil

• nutrients

• consumers

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NGSS.MS-LS1-5

Four students were asked to create a graph representing a typical predator–prey relationship. Which graph shows a situation in which the number of predators in a population depends on the number of prey?

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Black walnut trees produce a nontoxic chemical that becomes highly toxic when it is exposed to air or soil.

How does this chemical help black walnut trees compete with plants growing nearby?

• By attracting herbivores to the other plants

• By suppressing the growth of the other plants

• By increasing the photosynthesis rates in the other plants

• By limiting the amount of water available to the other plants

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After researching the diets of several birds inhabiting a nearby pond, a student goes on a field investigation to observe the feeding habits of the birds. The student records information from research and observations in the table. The student observes a great blue heron catching fish near the edge of the pond. Based on the information the student collected, which bird will compete with the great blue heron for the same hunting spots and similar prey?

• The mallard, because it hunts for fish while wading near the edge of the pond

• The pied-billed grebe, because it dives in open water to get crayfish on the bottom of the pond

• The great egret, because it hunts in water near the edge of the pond for fish and other prey

• None of these

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