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 4Construct hypotheses to explain biological phenomena: A) Propose hypotheses that are appropriate to the given scenario or question. B) Evaluate several hypotheses to select the one which best explains observations, or is best supported by data. C) Predict what would be most likely to occur under given experimental conditions in a test of... More, Inquiry 5Design experiments to test biological hypotheses: A) Identify the dependent and independent variables, and control and experimental treatments in any experiment. B) Identify situations in which no “control treatment” is appropriate, and design an experiment where subjects are tested more than once or the experimental treatment levels take a wide range of... More, Inquiry 6Create graphs from a data set. A) Decide what type of graph is the most appropriate type to display a data set. B) Decide to which axis each variable should be assigned in order to represent a specific hypothesis properly. See materials aligned with Inquiry 6 More, Inquiry 7Use experimental results to support or refute a hypothesis: A) Interpret graphs and/or raw data with respect to a hypothesis B) Distinguish correlation from causation, and correctly attribute phenomena to biological mechanisms. C) Demonstrate how to distinguish observations/data resulting from a specific cause from those caused by random chance. D) Explain why experimental evidence... More, Inquiry 8Interpret and communicate scientific ideas effectively: A) Use the conventions of scientific writing, including images and graphs, e.g. in laboratory reports. B) Interpret and paraphrase information from valid sources, such as the textbook and the primary literature. See materials aligned with Inquiry 8 More; SA/V 1Calculate the ratio of surface area-to-volume of an object, and explain why the ratio decreases as objects get larger and increases as objects get smaller. More, SA/V 2Explain how the ratio of surface area-to-volume plays a role in regulating: A) Rates of diffusion and osmosis B) Gas exchange C) Body temperature More; Gradients 1Explain what a gradient is and the role of gradients in: A) Homeostasis B) Thermoregulation C) Osmoregulation D) Chemical reactions associated with metabolism More, Gradients 2Identify whether a chemical or energy gradient exists in new situations More, Gradients 3Indicate the direction of energy or material movement under different conditions such as: A) Chemical concentrations B) Temperature C) Permeability of membranes More, Gradients 4Indicate the relative rate of energy or material movement under different conditions including: A) chemical concentrations B) temperature C) permeability of membranes D) varied shape (surface-to-volume ratio) More; Membrane Transport 2Explain how processes of transport work including: A) Diffusion i) Passive ii) Facilitated B) Osmosis i) Passive ii) Facilitated C) Active transport More, Membrane Transport 3Define the following terms, and explain how they relate to the movement of materials across a membrane: A) Isotonic B) Hypotonic C) Hypertonic More, Membrane Transport 5Predict how the following conditions affect membrane transport: A) gradient conditions B) temperature C) ATP availability D) changes in permeability E) molecule size, charge, or polarity More

Materials

Per lab group

• Dialysis tubing (3 different diameters) with clamps
• Hot plates
• Ice bath
• Vernier (or similar) temperature probes 
• Vernier (or similar) interface
• Vernier (or similar) ion probes –  or Potassium Ion-Selective Electrode or Salinity Sensor
• Salt solution
• Glucose solution
• Starch solution
• DI water
• IKI solution
• Beakers

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