When scientists study organisms in nature (i.e. outside of the laboratory), carefully controlled experimentation is not always possible.  In a case involving mating behavior of birds, data might be gathered by

Evidence suggests that an asteroid struck the Gulf of Mexico near what is now the Yucatan Peninsula about 65 million years ago.  What was likely the cause of the cause of the loss of many plants?

Which organ system plays the least role in maintaining optimal conditions of the animal body? 

The lungs and heart are located in the _____.

Why do viruses only infect specific types of cells?

In the vascular bundles of most dicot stems, primary phloem differentiates toward the ________of the stem, while primary xylem differentiates toward the ________of the stem.

An organism has the following features: diplontic life cycle, protostome development, segmentation, a septate coelom, closed circulatory system, and setae. To which phylum does this organism belong?

The closest extant relative of the Tyrannosaurus rex is the _____

A small island has stable populations of plants and animals, including one species of hawk as the only predator. The removal of the hawks could cause ____________ population size.

*Adult echinoderms display radial symmetry. What evidence suggests that echinoderm ancestors evolved from bilaterally symmetrical ancestors?