The northern boundary of the distribution of Saguaro cacti is defined by

A. areas in which temperatures do not drop below freezing.
B. the availability of water year round.
C. the presence of pollinating insects.
D. proximity to coastal environments.
E. the frequency of low-intensity fires.


A. areas in which temperatures do not drop below freezing.

Biology & Microbiology

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Examine Figure 23.21 in your text. According to the figure, a mass extinction has occurred at approximately the end of the:

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Where did information processing become increasingly centered in terrestrial vertebrates?  

A.  thalamus B.  forebrain C.  midbrain D.  hindbrain E.  medulla oblongata

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What is a GCM?

A) general climate model B) geographic climate model C) general circulation model D) geothermal climate model

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Microorganisms that typically live on human sur¬faces, including the interior tubes and cavities of the digestive and respiratory tracts, are called ____________.

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