This lab is best used as an introduction to osmosis. It allows students to observe what happens to carrots soaked in salt water overnight versus carrots soaked in fresh water. Students compare the physical characteristics of each type of carrot as well as the weights of the carrots.
Students are not only responsible for collecting their own data, but also have to share that data with the rest of the class. The total weight of the carrots in each category is recorded by each student. You can use a triple beam balance to weigh the carrots, but I have found that an electronic balance is much easier and more accurate.
The lab write up requires students to record their own data as well as the class data. It also has them create a bar graph and write a conclusion paragraph.
I have found this to be an easy lab to use - all you need are carrots, water, salt, and some small beakers or other containers (plastic cups could be used). I have found that students enjoy sharing their findings with the class and with other classes - if you have more than one section of a class you can compare the data from each class.