Question

Green and purple sulfur bacteria will carry out anaerobic photosynthesis primarily in
A) zone 1. 
B) zone 2. 
C) zone 3. 
D) zone 4. 
E) both zones 1 and 2.

Accepted Answer

Zone 3 is the aphotic zone where sunlight is not available to support photosynthesis. Green and purple sulfur bacteria use non-oxygen-containing compounds such as hydrogen sulfide or elemental sulfur as electron donors in photosynthesis, which allows them to carry out anaerobic photosynthesis. These compounds are usually found in the anoxic layer of zone 3, making it the primary area for these bacteria to carry out photosynthesis.