Michael Halverson Valhalla High School El Cajon, California
Research Host: Kim E. Barrett, Ph.D. University of California, San Diego 1997 Grade Level: High School
How Do Hypotonic, Hypertonic, and Isotonic Solutions Affect the Water Movement of a Cell? Purpose: The purpose of this activity is to teach students about osmosis and the effects of hypotonic, hypertonic, and isotonic solutions on animal cells. This lab is designed for high school biology students but may be adapted for middle school students. Objectives: The students will be able to describe osmosis and differentiate between the effects of hypotonic, hypertonic, and isotonic solutions on animal cells and determine the equilibrium point for a chicken egg in corn syrup. They will also be able to apply this knowledge to human colonic (large intestine) epithelium, and the effects and consequences hypotonic, hypertonic, and isotonic solutions would have on these cells. Materials: This activity is designed for an entire class (from 20 to 36 students) working in pairs or trios, so that the class is divided into 11 groups. Each group (2-3 students) of students will need the following: • one raw egg • vinegar (approximately 5% acetic acid) • beaker or container • paper towels (or tissues) • balance • corn syrup • distilled water (tap water will work) • graduated cylinder • tape • pen • 0.5 cm graph paper Ask each group of students to bring in one egg. It is much less expensive to purchase the vinegar and corn syrup in large volumes, if possible. Stores that cater to restaurants and businesses or sell foods and products in quantity, such as Smart & Final, Costco, Price Club, etc., may offer lower prices. Also, ask to see the manager or ask the cashier if the establishment has an educator’s discount. All they can do is say no! If you live near a farm or egg ranch, ask the owner or manager if they will donate eggs to the school or offer an educational discount. Preparation and Procedure: This is an excellent activity to accompany or follow a lecture on diffusion and osmosis, cells, and/or the digestive system. Dissolving the eggshell takes 36-48 hours (something you may want to start two days before introducing the topic...the students don’t need to know why they are doing this for now). The students can start dissolving the eggshells two days before you anticipate starting the activity or start the activity before a lecture or
other assignment and begin the activity after the assignment. After the shell is dissolved, the eggs should be placed in their respective solutions for a minimum of two days (something you may want to start on a Friday and have sit over a weekend). The activity involves each group of students dissolving the shell (composed of calcium carbonate, CaCO3) of an egg with vinegar, exposing the membrane. The teacher should assign each group of students (11 groups total) a concentration of corn syrup solution (0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%). After the shell is completely dissolved (about two days), each group will then make their assigned concentration of corn syrup solution. For instance, the 0% group will pour 500 ml of 100% distilled (or tap) water into their beaker, the 10% group will make a solution with 90% water and 10% corn syrup (450 ml of distilled water and 50 ml of corn syrup), and so on. The 100% group will pour 500 ml of 100% corn syrup into their beaker. After the assigned corn syrup solution has been made, the beaker should be labeled with the names of all students in the group, the date, the class period, and the concentration of corn syrup. Before placing the eggs into their solutions, each group should determine the dry mass of their egg (using a balance) and record it as the “beginning” mass. To determine the dry mass, the vinegar should be dried off the egg using soft paper towels. As soon as the dry mass of the...