Academic journal article The Science Teacher

Turning into Ice: Teaching Biological Ice Nucleation and the Global Water Cycle

Academic journal article The Science Teacher

Turning into Ice: Teaching Biological Ice Nucleation and the Global Water Cycle

Article excerpt

This article describes an interdisciplinary unit in which students explore biological ice nucleation--by particles that cause water to freeze at temperatures above -38[degrees]C--through the lens of the microbial ice nucleator Pseudomonas syringae. Such microorganisms are arguably some of the most important ice nucleators at temperatures above -15[degrees]C (Murray et al. 2012). The bacterium P. syringae has been found in clouds, rain, and snow. It produces an outer membrane protein functioning as an ice nucleus (Wolber et al. 1986; Morris et al. 2008; and Monteil, Bardin, and Morris 2014) and can initiate precipitation (Morris et al. 2014) (Figure 1, p. 38).

This activity, which aligns with the Next Generation Science Standards (see box, p. 43), exposes students to the global water cycle, highlighting the importance of critical and ethical thinking at the intersection of biology and engineering. Furthermore, the activity is designed to

* introduce students to principles of ice nucleation and allow them to recognize the diversity of ice-nucleating particles;

* allow students to recognize how interdisciplinary research can address complex problems across multiple fields of study, using ice nucleation and its relationship to atmospheric processes as an example;

* have students consider principles of experimental design, including the formulation of testable hypotheses and the inclusion of appropriate positive and negative controls in developing an ice nucleation test;

* have students design and conduct an ice nucleation experiment with known and unknown samples of undetermined ice nucleation activity; and

* highlight connections between systems of different scale such as microbiology (ice nucleation) and the global water cycle (bioprecipitation).

An interdisciplinary approach

The National Science Foundation (NSF) has called for interdisciplinary research approaches to environmental education (Vincent and Focht 2011). Ice nucleation and bioprecipitation are ideal systems for an interactive interdisciplinary curriculum that ranges from the molecular scale (ice nucleation protein) to a global scale (water cycle). Students consider and discuss new research, rather than going through prescribed lab exercises. The concept of a bacterium causing water to freeze increases student interest. Most students will be surprised to learn that pure water may stay in a liquid form down to about -38[degrees]C.

Part 1: The discovery of microbial ice nucleation (~5 minutes)

A plant pathology group discovered ice nucleation by P. syringae in the 1970s, noticing that plants infected with northern corn leaf blight showed increased frost damage. Considerable investigation revealed the causal agent of the increased frost damage (Lee, Warren, and Gusta 1995). In a story format, walk students through the discovery of biological ice nucleation without mentioning that P. syringae is the freezing agent, so that students can think about this as an "unsolved mystery" (see "On the web").

Part 2: Ice nucleation demonstration (~15 minutes)

Provide a demonstration of the ice nucleation phenomenon. First, place a glass bottle containing 100 ml of sterile nanopure water into an Alpha 12 cooling bath at -8[degrees]C (see Figure 2 for a supplies list). Next, add 4 ml of room-temperature water containing a single strain of ice+ P. syringae into a bottle and swish it around. The suspension in the bottle instantly freezes.

Part 3: Ice nucleation and bioprecipitation (~30 minutes)

Ask students to comment on the ice nucleation demonstration and make connections to complete the story they heard in the first part of the lesson. This lecture also discusses the concepts of ice nucleation; cloud formation via ice nucleation; and bioprecipitation, the idea that ice+ bacteria could make rain (Sands et al. 1982).

Part 4: Guided inquiry (~75 minutes)

In the fourth part of the unit, we present experimental design concepts to students. …

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