STAAR Biology - 7B-7D

After examining the fossil record, scientists have determined that scorpions today are much smaller than their extinct ancestors. For example, Jaekelopterus rhenaniae, a giant scorpion species that lived 255 million to 460 million years ago, was 2.5 meters long. Which of the following conclusions is supported by this information?

• Scorpions living today have increased their numbers since they first appeared.
• Scorpions in the fossil record are smaller than their descendants are.
• Scorpions have changed as a result of natural selection.
• Scorpions do not appear in their original state in the fossil record.

The cladogram shows the evolution of land plants as indicated by fossil records.

Which discovery would challenge the validity of this cladogram?

• A large aquatic vascular plant about 200 million years old
• A species of algae that has existed for less than one million years
• A moss species that has existed for less than 380 million years
• A fossil of a fern more than 425 million years old

This diagram of the fossil record represents changes in mollusks over millions of years.

How can the pattern of change in the fossil record best be explained?

• The mollusks were well adapted to their stable environment. A large, sudden change occurred in their environment. After the change the mollusks with the bigger shells were better adapted for the new environment.
• The mollusks were well adapted to their stable environment. The mollusks hybridized with a smaller species of mollusk. A new species of mollusk with a bigger shell resulted.
• The mollusks were not well adapted to their environment. The length of the mollusks’ shells changed gradually over time. The mollusks in the original population that had small shells died over a period of many years.
• The mollusks were well adapted to their environment. Humans introduced a new species of mollusk that was not adapted to this environment. The introduced mollusk outcompeted the native mollusk species.

Genetic variation can aid in the survival of species when the environment changes. Which of the following is the best example of an organism with a genetic variation that could improve survival chances over time?

• An ant that is resistant to pesticide
• A wasp that is infected with parasites
• A cactus that has no spines
• A mouse that has learned to avoid mousetraps

Which condition is essential for natural selection to result in a new species?

• Unlimited resources
• An inherited variation
• A static environment
• A long life span