By Alex Cardonick, V Form

Biology: Membrane Structure and Function

Editors’ Note: In Advanced Biology, students are often evaluated on the reflection of their learning process. They constantly ask themselves questions that demonstrate advanced scholarship such as “How am I connecting each part of my learning into a flowing story?” and “What do I still not understand?” This form of deep reflection is summarized in each student’s ePortfolio at the end of a unit, which includes several different Learning Outcomes ranging from “Dynamic Homeostasis” to “The Central Dogma of Biology.” These Learning Outcomes are often present throughout multiple units, and therefore challenges the students to synthesize information across different areas of focus.

Linked here is Alex Cardonick’s ePortfolio on Learning Outcome 6: Membrane Structure and Function, including four Artifacts of Learning, including text, video, and images.

Introductory Narrative:

Cell membranes act as the “guards” of the cell. Membranes’ structure consists of phospholipids tightly knitted together by their hydrophobic tails, with the hydrophilic heads sticking out on either side. This phospholipid bilayer structure makes membranes semi-permeable; they let small, non-polar molecules such as water and carbon dioxide in, while keeping out large and polar substances such as starch and Iodide anions. In addition, cell membranes can be modified to help cells perform specific functions. Proteins added into the phospholipid structure can create transport channels for molecules that cannot travel through the membrane itself, such as Na+ ions in the nerve impulse. These ions allow a neuron to send a signal in the form of an action potential. Furthermore, molecules and ions can even move against the concentration gradient by active transport when a transport protein and outside energy are provided. This type of movement across a membrane allows essential functions such as the repolarization of the nerve impulse to occur when Sodium-Potassium pumps “reset” the nerve impulse to its resting membrane potential by moving the ions against the concentration gradient. (more…)