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A geneticist is studying sexual reproduction of a species of butterfly that lives in a very cold climate.  He hypothesizes that there should be low genetic diversity because it is well adapted to the cold climate but does not seem to be able to colonize surrounding areas with warmer climates.  What important principle is he using to formulate his hypothesis?

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

A primary tissue types that consists of scattered cells in a noncellular matrix is _____ tissue.

The tissue whose function is to move oxygen, carbon dioxide, nutrients, wastes, hormones, and heat around the body is _____.

On this temperature versus precipitation graph, the four areas plotted represent the ranges of temperatures and precipitations typical of four major types of biomes. Which choice correctly identifies the temperature and precipitation profiles for each type of biome?

Which of the organ systems listed below plays the most important role in protection of the human body from invasion by pathogens? 

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

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?

The first stage in the gametophyte generation is  _____.

Extinction of species is often the result of interaction with other organisms.  Which of the following is NOT an organism-induced cause of extinction?