Ecology and Ecosystems QBA Exam 1 Practice Test

The main idea here is lake zonation by light. The sunlit open-water zone where photosynthesis happens is the limnetic (open-water) zone. Below that in very deep lakes, light no longer reaches and the deep, dark layer is known as the profundal zone. This term specifically describes the deep, low-oxygen, detritus-driven portion of a lake's interior. While “aphotic” conveys lack of light, the conventional label for this deepest, dark lake layer is profundal. The abyssal zone is an oceanic term, and wetlands are a different habitat altogether.