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?

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 —

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?

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 —

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 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

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?

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?

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 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?

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 —

The Prairies Region and the Cross Timbers are located in north-central Texas. The graph below shows information about eating habits of white-tailed deer in these regions.

A Cross Timbers rancher is concerned about competition between the ranch animals and the deer. Based on the graph, which ranch animals compete for the most food with white-tailed deer?

A scientist named Joseph Connell studied two species of barnacles on the shore of a Scottish island. In the area between the average tide and the neap high tide, he found that the population of Species A was smaller than that of Species B. He removed Species B from one area but left both Species A and B in a similar area. The graph below shows the results of this study.

Based on these data, which hypothesis was Connell most likely testing?

Fish in a lake have to compete for space. Different fish have different optimal temperature ranges. The graph below shows the temperature ranges of four fish species.

At which temperature range will there be the most competition for space among these fish species?

The graph below shows the percent of seeds from two plant species that sprout when grown in water containing different amounts of salt.

Which of the following best summarizes the effect of saltwater on these plant species?

Which organisms in the food web shown above compete for the same food source in this environment?

The Couch’s spadefoot lives in Texas and has the characteristics listed below.

The Couch’s spadefoot is adapted to a certain type of environment. Which of these resources is most likely scarce in this environment?

This diagram shows the variety of organisms that live in different tide zones. Mussels are common organisms that compete for space in intertidal (middle) tide zones. If all of the mussels were removed from zone A, which organisms would likely compete for the space in Zone A?