Sea to Shore Lab: Diffusion

Why is diffusion through a membrane sometimes faster?

Overview

This lab should help students understand the extremely important role of gradients. Focus on the idea that gradients occur whenever there is a concentration difference from high to low. Gradients do not just occur in liquids there can be gradients in temperature, Na and K ions, smoke, perfume, people, etc.

Students should be familiar with the terms solute, solvent, hyper-and hypotonic. Osmosis refers to the movement of water and dialysis typically to the movement of solute. Students may or may not comprehend the concept of ion, but you can simply leave it as a charged atom or particle or molecule. Unfortunately, if they don’t have some clue about ions or at least that NaCl becomes Na+ and Cl- when dissolved, the understanding what conductivity tells them is difficult. The pre-lab explains it, but be prepared.

Outcomes:  Inquiry 4, Inquiry 5, Inquiry 6, Inquiry 7, Inquiry 8; SA/V 1, SA/V 2; Gradients 1, Gradients 2, Gradients 3, Gradients 4; Membrane Transport 2, Membrane Transport 3, Membrane Transport 5

Materials

Per lab group

Shaw, T.J. & French, D.P. (2018). Authentic Research in Introductory Biology, 2018 ed. Fountainhead, Fort Worth.

Assessments

PreLab Activity

Quiz

Keys and additional instructor-only notes (you will be asked to sign into a Google account and request access to view instructor materials)

Lab report rubric

Gradients and Membrane Transport

Outcomes:  Gradients 2, Gradients 3, Gradients 4; Membrane Transport 2, Membrane Transport 3, Membrane Transport 4, Membrane Transport 5; Thermoregulation 7

Prerequisite objective:  Membrane Transport 1

  1. Ask students to work in groups to complete a table to compare and contrast modes of transport. (Membrane Transport 2)
Diffusion Facilitated diffusion Active transport
Description Passive movement of… Passive movement of… Active movement of…
Are proteins involved? (yes/no) No

Follow up with clicker questions on how gradients relate to membrane transport. (Gradients 3, Gradients 4, Membrane Transport 3, Membrane Transport 5)

  1. (Gradients 4, Membrane Transport 5) Show an image of the activity at a cell membrane, that demonstrates that there are lots of materials moving in and out of cells (see example below). Ask students to brainstorm for 3 minutes about factors that can affect how quickly this transport occurs. In our experience, the list often contains factors such as:  temperature, membrane permeability, size of chemical gradient, and sometimes cell shape. Formalize the role of cell shape with the concept of surface area-to-volume ratio. Most cells are very small to maintain high SA/V, facilitating an optimal rate of material movement. Learn.Genetics has a great demonstration of cell size and scale here. Students may or may not have identified temperature as a factor with enzymes in mind. This is also a good opportunity to address Thermoregulation 7:  enzymes work best at a narrow temperature range.

 

  1. After introducing students to gradients and membrane transport, you may want to engage them in one of the following case studies:
    • Osmosis – Agony and EcstasyThis case follows Susan, an intern at a local hospital, who has admitted a patient she discovers has used the drug Ecstasy. The girl becomes delirious, and Susan begins to suspect that she may be suffering from water intoxication. (Membrane Transport 2, Membrane Transport 3
    • Osmosis – Osmosis is Serious Business!This directed case study involves two “stories,” each one concerned with some aspect of osmosis in living cells. Part I is centered around the effects of a hypertonic environment on plant cells, while Part II focuses on the effects of a hypotonic environment on human cells. (Membrane Transport 2, Membrane Transport 3
    • Membrane Structure and Transport – Newsflash! Transport Proteins on Strike!This role-play case study teaches students about plasma membrane transport and the functions of transport proteins in the phospholipid bilayer. Students act out the parts of molecules and structures in a fantastical cellular world where the unionized transport proteins have called for a work stoppage. (Membrane Transport 1, Membrane Transport 2, Membrane Transport 4)