Lab 10: Supercooling and Ice Nucleation

Introduction

In this lab, we investigate the nucleation of ice by the bacterium Psuedomonas syringae (Ps) which nucleates ice formation at temperatures as high as -2 of -3 degrees C. Water is supercooled from 0 to -40 degrees C and will not form ice without a nucleus at those temperatures. The freezing point of water is therefore -40 degrees C, whereas its melting point is 0 degrees C (along with the supercooling point).

Key Questions

  1. Why have bacteria evolved with the ability to nucleate ice formation?

  2. How did performing this experiment affect your understanding and accceptance of the concept of bacterial ice nucleation?

  3. Why do Ps bacteria on the leaf structures promote frost damage to plants?

  4. What is a “control” and how did you use a control in this experiment?

Procedure

Materials:

  1. Ice

  2. Water

  3. Ethanol slurry baths

  4. Thermocouples

  5. Test tubes

  6. Clamps

  7. 3 candidate P. syringae cultures

  8. E. coli cultures

  9. Doubly distilled water.

First we prepared an ice bath with dry ice and ethanol. Then we measured their temperature. T3 measured the temperature of the ice bath. Probe T1 measured the temperature of the PS sample and T2 measured the temperature of the E. coli sample.

Our ice bath was chilled to -27 degrees C.

Results

Discussion