In lesson 10, we continued with our study of osmosis, focusing on the extreme environment of the Great Salt Lake. Students learned that a railroad causeway was built across the lake more than 60 years ago, physically separating the lake into two sides. Only the south side of the lake receives a continuous supply of freshwater, causing the salinity of the south side to be much lower than the north side. As a result, the ecosystem of the south side of the lake is much more robust than the north side which is inhabited primarily be halobacteria. Considered extremophiles because of their unique ability to live in extremely salty water, halobacteria are present in such abundance that they color the water in the north side of the lake purple (because of the rhodopsin protein they produce). As evidence of their learning, students completed a case study worksheet and hypothesized what might happen to the existing Great Salt Lake ecosystem if the causeway were removed.