This lab takes about 20 minutes on one day, then it must sit overnight, and 20 minutes the next day. More time may be required for finishing the write-up. This is a simple lab that uses potatoes placed in fresh water and salt water to compare the osmotic issues that fresh and salt water creatures face. If you have a 90 minute period, I have found that it will work if you do the first half immediately and then wait 45 minutes to do the second part, rather than overnight. The first 2 pages are fine for grade levels 6 through 12. The last few questions on the 3rd page may be difficult for younger students....but then you can just leave it out or create questions of your own.