8.11a

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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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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List the steps of the scientific method

d

e

f

c

b

a

Communicate results

Analyze results

Conduct experiment

Draw conclusions

Ask a question

Form a hypothesis

Which letter represents amplitude? (a)  

• A

• B

• C

• D

• E

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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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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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The graph below shows the range of water conditions preferred by three species of fish in an Ozark stream.

Water with which of these conditions would cause the most competition for resources among all three species of fish?

• Very cold, very clear, and very fast

• Very warm, very clear, and very slow

• Mild temperatures, some suspended particles, flows very fast

• Mild temperatures, some suspended particles, flows at a medium speed

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Barnacles are marine organisms that live attached to surfaces as adults. A scientist studies two barnacle species that live on rocks on a coast in Scotland. In some rocky areas Species A is found alone. In other rocky areas Species B is found alone. In still other rocky areas both species are found together. The diagram below shows the two barnacle species on rocks in their habitats.

If Species B were removed from the rocky areas it shares with Species A, Species A would most likely inhabit —

• Zone I only

• Zones I and II only

• Zone III only

• Zones I, II, and III

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