Chapter 13

Distinguish between the following: gram-positive bacterium and gram-negative bacterium; fimbria and pilus; endospore and akinete; virus and viroid.

Pear decline is so-called because it causes a slow, progressive weakening and ultimate death of the pear tree. It is a systemic disease caused by phytoplasmas. What is meant by a "systemic disease," and by what pathway do phytoplasmas move through the tree?

One might argue that viruses should be considered living organisms. By what criteria might viruses be considered alive?