Diffusion Lab (Day #1 of 3)

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Objective

Students will 1. Investigate the effect of molecule size on diffusion through a semi-permeable membrane. 2. Collect evidence and use it to develop a claim and compose an argument about the permeability of an artificial membrane. 3. Use a scientific model to share and expand one’s thinking about the nature and function of cell membranes.

Big Idea

Cell membranes are semi-permeable. Diffusion of substances across the membrane is driven largely by the size of the solute particle.

Learner Goals

Note: I recommend that you first check out this resource in order to get the most out of this lesson!

In high school I took several drafting classes and, for a while, I had hoped to become an architect. With respect to planning instruction and teaching, I feel that I can still live out the detailed approach to building something intricate and complex even though the product is a lesson rather than a certain "built environment".

The lesson-planning document that I uploaded to this section is a comprehensive overview of how I approach lesson planning. This template includes the "Big Three" aspects of the NGSS standards: Disciplinary Core Ideas, Crosscutting Concepts, and Science Practices. Of course, there are many other worthy learning goals, skills, instructional strategies, and assessments that can be integrated into a class session. I don't feel compelled to check every box but, rather, use it as a guide to consider various options and tailor the lesson in light of these.

With regard to this particular lesson, students will be able to:

1. Investigate the effect of molecule size on diffusion through a semi-permeable membrane.

2. Collect evidence and use it to develop a claim and compose an argument about the permeability of an artificial membrane.

3. Use a scientific model to share and expand one's thinking about the nature and function of cell membranes.

I hope you get some value from my work! Please find the more intricate details of this lesson plan in the uploaded document!

[Note: Refer to the planning document for specific details throughout the three day investigation]

Anticipatory Set ("Hook")

5 minutes

Word Wall: To begin with, students are provided a copy of the Diffusion Lab Template that, with my guidance, will be fully completed by the start of tomorrow's investigation. Next, I verbally review a short list of key vocabulary with them so that, as these terms are used over the course of this three day lesson, their familiarity will be much stronger. Refer to the teacher version of the Diffusion Lab Design PPT and slide #2.

Instructional Input/Student Activities

45 minutes

Teaching Challenge: Use a scientific model to share and expand one's thinking about the nature and function of cell membranes.

The heart of this, and any other, investigation is to lead students to the point where they can pose a meaningful scientific question, make a reasonable and testable prediction, and devise a method for collecting evidence with which to answer the original question and compose a thoughtful argument about the related phenomenon.

To this end, as we do investigations again and again throughout the year, I expect that student proficiency gets better and better. Toward the end of the year, student teams ought to be able to take off on their own with only a question posed to them by me. Of course, true inquiry is difficult to impossible to carry out in most teaching and learning contexts due to constraints of time and resources but this is still a worthy goal to shoot for.

Therefore, as I guide students through the process of designing their labs, I ask a lot of questions and try to have them fill in the blanks as much as possible. Again, as I described earlier, this format should be familiar to them, having done this before.

The main object of study in this lab is the structure and function of a typical cell membrane. Due to the small-scale size and fragility of the membrane, the dialysis tubing is substituted as a model. Quickly, students grasp the point of this and are eager to see how it works in real life.

According to the details laid out on slides #3-13 of the Diffusion Lab Design PPT and lesson-planning document, I walk students through the first two pages of the student Diffusion Lab template handout.

To aid in dividing up the workload, I assign half of my eight teams to investigate whether glucose is permeable to the dialysis membrane and the other half to do so with starch. At the end of the experiment, the evidence collected will be shared out and analyzed with respect to the question of permeability.

Closure: What did we learn? Where do we go from here?

5 minutes

Review of Lab Essentials: I quickly review the essentials of the key variables for tomorrow's lab (MV, RV, CVs, ECC) as outlined in the lesson-planning document.

Continue to Day #2...

Lesson Extension & Follow-Up Activities

Students ought to complete the remainder of the lab design from Section #1 (Question) through Section #4 (Materials).