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Biology: Membrane Structure and Function

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.


When studying this LO, I think that I was successful because when I came across difficult concepts, I broke them down to the simple ideas that I already knew. I used my learning about the fluid mosaic model of the cell membrane and the three types of molecular movement across a membrane to make complex processes, such as the nerve impulse, be more manageable to learn. When I was given a new challenge, such as in my cell membrane EBE, I made sure to focus on what I knew before worrying about the complex details. I always looked for concentration gradients, transport proteins, and molecule types to break down a new concept. This significantly benefitted my study of the NMJ, as I was able to understand why certain molecules use or do not use certain proteins to travel in specific directions. By starting small, I was then able to shift to the “big picture” by looking at how molecular movement allowed the NMJ’s endomembrane system to function as a whole.


Alex Cardonick is a V Form boarding student from Glencoe, IL. His academic interests are STEM and business, and he plays hockey and golf.

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