Academic journal article The Science Teacher

Investigating Membranes: Using Artificial Membranes to Convey Chemistry and Biology Concepts

Academic journal article The Science Teacher

Investigating Membranes: Using Artificial Membranes to Convey Chemistry and Biology Concepts

Article excerpt

[ILLUSTRATION OMITTED]

While not organic in nature, quick-"growing" artificial membranes can be a profound visual aid when teaching students about cellular processes and the chemical nature of membranes. Students are often intrigued when they see biological and chemical concepts come to life before their eyes. In this article, we share our approach to growing artificial membranes in the classroom, discuss their similarities to and differences from cellular membranes, and explain the related processes and principles they demonstrate for students.

Artificial membrane formation

Though not widely studied today, artificial membranes were researched quite extensively in the early 20th century by Stephane Leduc, a professor at L'Ecole de Medicine de Nantes (Zeleny, Klir, and Hufford 1988). Leduc published his findings in The Mechanism of Life (1911), in which he used the membranes as a morphological model for spontaneous growth. However, the notion of spontaneous generation was vehemently rejected during Leduc's time. Due in part to this prevailing belief and a lack of understanding about how these membranes are formed, his findings fell into obscurity.

Today's scientists, however, have a better grasp on how artificial membranes are contrived. The formation of artificial membranes is frequently confused with the development of crystals, which occurs by accretion. Accretion results when each atom is laid on top of another (i.e., like building blocks). As this occurs, the atoms, ions, or molecules involved take on a specific arrangement. Often, flat surfaces with specific angles are formed to produce ordered shapes.

Artificial membranes, on the other hand, arise through a process called "intussusception." Intussusception is the folding of an outer layer, which forms a pocket on the surface. Cell membranes grow larger by the deposit of new particles between existing particles in the cell membrane. When intussusception occurs, chemicals, atoms, or molecules react together to insert new particles between the outer layer of the pocket that has formed on the surface of the reacting chemical--thus, various chemicals react to actually form a new substance.

In our class on exploring artiicial life, we demonstrate the growth of artiicial membranes from calcium and phosphate ions. The materials and methods we use are outlined in Figure 1 (p. 42). When calcium chloride (Ca[Cl.sub.2]) and sodium phosphate ([Na.sub.3]P[O.sub.4]) interact, there is a strong enough attraction between the oppositely charged ions to form new products. The ions form the insoluble ionic solid [[Ca.sub.3][(P[O.sub.4]).sub.2]]--the precipitate that the membrane is composed of--and soluble sodium chloride (NaCl). The reaction is represented by the following balanced equation: 3Ca[Cl.sub.2] (s) + 2[Na.sub.3]P[O.sub.4] (aq) [right arrow] [Ca.sub.3][(P[O.sub.4]).sub.2](s) + 6NaCl(aq).

The thin, hollow tube that is formed identiies the resulting precipitate as a membrane rather than a crystal. This tube is selectively permeable--it allows some substances to pass through it but prevents others from doing so.

Selective permeability

Selective permeability is one of the defining characteristics of a membrane and is a key component of cellular regulation in living organisms. Biological membranes are complex entities that are formed from lipids. These lipids are embedded with various types of proteins and carbohydrates that serve specific functions such as identification, signaling, and transport of substances across the membrane.

FIGURE 1

Methods, materials, and results.

To grow membranes in our classroom, we used an anhydrous
calcium chloride and sodium phosphate solution
that was saturated at 25[degrees]C. A 250 mL beaker was
filled with 200 mL of saturated sodium phosphate
solution, prepared by adding sodium phosphate until
no more could dissolve and then filtering out the few
remaining grains. … 
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