Acidophilic organisms live in low pH environments. Neutrophilic organisms thrive in environments with pH
values closer to 7. Alkaliphiles grow best in high pH environments. All of these organisms, regardless of the
external environment, maintain a constant internal pH less severe than that of the environment they inhabit.
Thus, the adaptation to extreme pH is accomplished by moderating internal pH changes as well as evolving
molecular adaptations to extreme pH. An example of this ability to maintain constant internal pH is shown in
Textbook Figure 5.11

1. Under typical conditions with a neutral pH, how does E. coli set up a proton gradient across its plasma
   membrane? What does it use this gradient for? (2 points)
2. Look at Textbook Figure 5.15.How is the neutralophile E. coli able to deal with low external pH? With high
   external pH? (2 points)
3. Look at Textbook Figure 5.14. What special use for Na+ have alkaliphiles developed? Why is this necessary
   in a high pH environment? (2 points)
4. Extrapolating from your answers above, how might acidophiles maintain internal pH and still transport
   solutes, operate flagella, and so on? (4 points