We need oxygen, and photosynthesis in plants supplies it. But so do a group of viruses. It is amazing how things evolve:- http://www.newscientist.com/article/mg20327235.000-photosynthetic-viruses-keep-worlds-o... in the amazing category is sensory perception, when eyes are of little use or not present at all. Sensing an enemy or prey:-http://www.sciencedaily.com/releases/2009/08/090828103932.htm