Academic journal article The Science Teacher

Modeling a Membrane: Using Engineering Design to Simulate Cell Transport Processes

Academic journal article The Science Teacher

Modeling a Membrane: Using Engineering Design to Simulate Cell Transport Processes

Article excerpt

This article presents a unit in which the engineering design process described in the Next Generation Science Standards (NGSS Lead States 2013; see box, p. 38) was used to design and build a functional model for cell transport.


The plasma membrane, which controls what comes in and goes out of a cell, is integral to maintaining homeostasis. Even small defects that cause some loss of function of the plasma membrane can result in major disorders, such as cystic fibrosis and Duchenne Muscular Dystrophy (DMD). This common type of muscular dystrophy is caused by a mutated dystrophin gene on the X chromosome. DMD prevents the proper formation of the cell membrane in the cells of the muscle fiber.

Cell transport of small molecules across the cell membrane happens in several different ways. Some small, non-polar molecules cross the plasma membrane along the concentration gradient directly through the phospholipid bilayer, a barrier around the cell composed of two sheets of lipid molecules. Other smaller charged particles, such as water molecules and charged ions, cross the membrane via channel proteins through the process of facilitated diffusion. Some substrates may need to be pumped across the membrane against the concentration gradient, which requires an energy input or the help of carrier proteins to cross the membrane via active transport.


In this unit, high school biology students designed a functional, three-dimensional model of a plasma membrane for cell transport. The model plasma membrane needed to allow different substrates to cross it via a variety of transport proteins. The model imitated the function of the phospholipid bilayer and incorporated channel proteins and carrier proteins to transmit four materials that represented different types of substrates that would need to enter or exit a cell.

As students used the engineering design process to design and build an artificial cell membrane, they learned about the structures and functions of each part of the phospholipid bilayer and the processes of osmosis, diffusion, facilitated diffusion, and active transport (Figure 1). This engineering unit was inspired and adapted from an engineering design challenge called Keepers of the Gate from TeachEngineering, an online curriculum (see "On the web").

Lesson 1: Introducing the engineering design process

The first lesson introduced the engineering design process and how it relates to scientific inquiry. Addressing the question, "What is the engineering design process?" students discussed their ideas of how engineers solve problems, then the teacher introduced the Engineering is Elementary design process created by the Boston Museum of Science (see "On the web"). Although this simple description, which includes five steps (ask, imagine, plan, create, and improve), targets an elementary engineering curriculum, it's effective with high school students unfamiliar with the engineering design process. As students learn more, teachers may offer more complex representations, such as the six-step process from NASA, the seven-step process from Teach Engineering, or the eight-step process from Engineering Everywhere (see "On the web").

Next, the teacher asked: "What is the process of scientific inquiry?" After student discussion, the teacher introduced a modified version of the science inquiry map created by the System-wide Change for All Learners and Educators (SCALE) program (see "On the web"), which highlighted four essential components of inquiry:

* asking a scientific question,

* gathering evidence,

* making a scientific claim, and

* communicating results.

The Claim, Evidence, Reasoning (CER) model for creating a scientific argument was practiced regularly so that students could support their claims with derived evidence and connect them to general scientific knowledge (McNeill and Krajcik 2012). …

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