37.  The most productive region of a lake is the ____ zone.

29.  The primary reason that Earth experiences seasons is because of the:

13.  Habitat is best described as:  

44.  Today, the major danger to species is:

41.  Building roads, parking lots, building and bridges all contribute to:

21.  Approximately what proportion of the radiant energy entering an ecosystem is used in photosynthesis?

11.  A biological community and its abiotic environment together comprise which of the following?

7.  An example of a density dependent factor that influences the size of a population is:

38.  Which of the following applies to the deepest zone of a large lake?

39.  The ___ realm has long been separated from other land masses and is the area in which marsupials are particularly common.