Living in an Alkaline Environment
Activity ProcedurePart 1 Part 2 Part 3
Part 1: How different is Mono Lake water from Distilled water?
If you want your students to mix their own simulated Mono Lake water, have them do this as Step 1. If you are providing prepared Mono Lake water at the stations, begin at Step 2.
Mixing one's own Mono Lake water dramatically demonstrates the large amount of dissolved solids in the water. This insight is important to understanding just how extreme Mono Lake is as a habitat. Students will get more out of the activity by making their own Mono Lake water.
See the Preparation Section for the materials and amounts required to make simulated Mono Lake water. For comparison, 1 quart of seawater has 30.8 g of chloride salts. 0.2 g calcium carbonate, and 6.0 grams of magnesium sulfate. The pH of seawater is around 8 (versus 10 for Mono Lake) and its average specific gravity is 1.025.
SAFETY NOTE: SODIUM HYDROXIDE IS CAUSTIC AND CAN CAUSE SKIN BURNS. STRESS CAREFUL HANDLING. MAKE SURE STUDENTS WEAR GLOVES AND EYE PROTECTION.
Have student teams examine the simulated Mono Lake water by rotating through the activity stations 1-4. Have each student record his/her observations on the student handout.
Masters for the student sheet and the activity station instruction cards are provided at the end of this activity.
Stations 5 and 6 are most easily and safely done as teacher demonstrations.
Station 5: Test whether Mono Lake water produces a chemical change in the egg white's proteins. Place several teaspoons of fresh egg white into a beaker. Place several teaspoons of the egg white-Mono Lake water solution in a second beaker. Make sure both beakers can withstand boiling water. Add boiling water to the beaker with the fresh egg white. Have students observe how its proteins coagulate, turning into a mass of white, solid strands. Next, add boiling water to the egg white-Mono Lake water. The egg's proteins were denatured by the Mono Lake water and do not coagulate. Since egg white's normal response to boiling water is to coagulate, this different response to boiling water suggests that the Mono Lake water significantly affected the egg white's protein, creating a new chemical product with new chemical properties. Have students record the results of the test on their student sheets.
Station 6: Compare how distilled water and simulated Mono Lake water effect cells. Prepare a slide of check cells. Place the slide on the stage of a microscope whose image can be displayed on a computer or projection screen. First, draw distilled water across the slide by placing several drops of water along one edge of the coverslip. Place a tissue or other absorptive material along the opposite edge of the coverslip. (The water will be drawn under the coverslip.) Repeat this procedure with the simulated Mono Lake water. The Mono Lake water's high salt content draws water out of the cell by osmosis, causing them to shrivel.
Assign students the five worksheet questions.
Questions 1-4 reinforce the concepts introduced in Part 1. For Question 4, students can either speculate with their best thinking or consult references to prepare answers based on established ideas in cellular biology. Question 5 asks students to make a prediction, which they will test in Part 2. Make sure to review Question 5 before beginning Part 2, and review students' answers to all the questions, if possible. Back to Top
Part 2: How do alkaline environments affect bacteria in our environment?
Have student teams follow the protocol outlined on the student sheet, which has them use soil bacteria from the local environment to inoculate four plates with pH ranging from 7 to 10.
SAFETY NOTE: Sodium hydroxide is a powerful, caustic material. Because of its ability to break down fat and proteins, it is the active ingredient in many drain cleaners. Since skin is largely fat and protein, sodium hydroxide can cause skin burns if improperly handled. REMIND STUDENTS TO USE CARE. MAKE SURE THEY WEAR GLOVES AND SAFETY GOGGLES.
After 24-48 hours, have students examine the growth on each of their plates.
The time required to grow the colonies depends on the number of bacteria in the sample and the incubation temperature. At room temperature, students should be able to see small dots within 24 hours and colony formation after 48 hours. If you are able to incubate at 35-37 degrees C, colonies should be visible in 24 hours. A suggested timetable for room-temperature culturing is: Day 1: Inoculate plates; Day 2: Initial observation (5 - 10 minutes to observe small colonies); Day 3: Final observation (developed colonies) and graphing.
Have students create a graph comparing the number of colonies and the pH.
Survival patterns decline as pH increases. Above pH 9, little or no growth is anticipated. On a graph (right), the expected trend would be:
To show that bacteria can live at high pH, have students look at the Mono Lake images on the MBL's microscope. Have the class brainstorm a list of adaptations that organisms living in extremely alkaline environments (e.g., Mono Lake) might have.
In Part 3 of this activity, students will examine the ecology of Mono Lake. They will explore adaptations for living in highly-alkaline environments and create a food web illustrating energy transfer in this extreme environment.
Have students answer the questions on the handout. Back to Top
Part 3: A WebQuest Exploring the Life and Ecology of Mono Lake
Part 3 is a web-based inquiry activity. This WebQuest is designed for individual participation, but can be modified for small groups. It is recommended that you introduce evaluation procedures and review food web concepts prior to beginning the activity. Refer to the Teacher Page for additional information.Back to Top