All animals must get oxygen for respiration.  Which of the following is NOT involved in this critical function?

Why are parasites so difficult to classify based on morphology only?

Homeostasis in animals can be generally defined as the _____.

Which ecosystem would be least affected if sunlight did not reach the Earth for an extended period of time?

The outermost layer of the stele of a root is the _____.

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

A major evolutionary innovation that freed reptiles from water for a life on land was the ______

Many indicators show that temperatures are increasing, and climate patterns are changing on a global scale.  What is NOT a likely result of these changes?

What feature is shared by members of both the phlyum Chordata and the phylum Echinodermata?

Recent extinctions of species can be attributed to several causes.  Which of the following is not considered a major cause of such extinctions?