Water on the Move: Osmosis (#1 of 3)

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Students will be able to understand the hierarchical nature of multicellular organisms. Furthermore, students will be able to model the process of osmosis and predict and explain its outcomes given the conditions of the environment.

Big Idea

The structure of the cell membrane in addition to specific internal and external conditions dictate how water diffuses sometimes with drastic results!

Learner Goals

Photo Credit: "Oncorhynchus nerka" by Timothy Knepp of the Fish and Wildlife Service. - US Fish and Wildlife Service. Licensed under Public Domain via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Oncorhynchus_nerka.jpg#/media/File:Oncorhynchus_nerka.jpg                                          

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...

1) Understand that multicellular organisms have a hierarchical structural organization, in which any one system is made up of numerous parts and is itself a component of the next level. (LS1.A)

2) Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. (HS-LS1-2)

3) Generate a logical conclusion that is supported by evidence from the investigation and/or provide a scientific reason to explain the trend in data given a description of and the results from a scientific investigation. (WA-INQC-1)

I hope you get some value from my work!

Anticipatory Set ("Hook")

10 minutes

First of all, I should explain my choice of my anchor picture; you know, the big red fish. Considering that I hail from Washington state and we are home to a pretty amazing and vast array of wildlife, I decided to feature the adult male Chinook salmon (of the spawning variety). I don't understand the full details but there is a distinctive color change as a result of a combination of hormonal, neural, and environmental cues.

I recognize that salmon exist in many other locales but the salmon is an iconic Northwest fish (and the many sport fishers coming here attest to this fact).

Secondly, it lives a dual lifestyle. After it hatches and matures in fresh water, it migrates downstream to the oceans and continues its maturity there thus dealing with two very different osmotic conditions. As a case study to adapting to the environment, I think that the salmon is a pretty good choice (if I say so myself)!

Teaching Challenge: How do I support students to develop and use scientific models?

Teaching Challenge: How can I increase/improve my students’ use of appropriate and precise scientific vocabulary?  

1) Word Wall- Provide the definition for each of the following terms on the SMART board: solute, solution, concentration, concentration gradient, osmosis, equilibrium

2) Entry Task- Prompt students to label the Osmosis Practice handout with the following details:

  • Name the cell, cell membrane, solute, concentration gradient
  • Count and record the number the solutes inside and outside each cell

Instructional Input/Student Activities

45 minutes

Teaching Challenge: How can I develop my students’ ability to apply unifying ideas to make connections across science content (among and between physics, chemistry, biology, earth and space science)?

Introduction to Osmosis

To this point in the curriculum, students will have created a 3D model of a cell, investigated the salient features of animal and plant cells, learned about the structure and function of a typical cell membrane, investigated semipermeable membranes and the process of diffusion, and have been equipped with specific vocabulary.

Therefore, the challenge now is to begin assembling a more complex understanding of cell processes (i.e. osmosis) and their relationship to real-world applications.



1) Predict-Observe-Explain (Part #1 of 2): Student teams will be provided with a basic question and supplies. Their task is to create a reasonable prediction (relating the effect of solute concentration on water movement), quickly set up the qualitative demonstration, and wait for approximately 25 minutes for the process to run its course. This should be very simple since students have completed a handful of full-blown inquiry style labs to this point.

In the interim, we will begin unpacking the concept of osmosis and the three possible outcomes of water movement given different external and internal solute concentrations.

2) Osmosis Lecture & Problem Solving (Part #1 of 2): 

Word Wall: Provide the definition for each of the following terms on the SMART board: hypotonic, isotonic, and hypertonic

Introduction (Slides #2-13): I do a quick overview of the problems that cells must solve to even be alive, then review the three osmotic conditions that cells encounter with an emphasis on ideal conditions for both animal and plant cells.

Solving Osmosis Problems (Slides #13-26):

(Pedagogical Sidebar) "Name the Steps" Technique: By breaking down a conceptually challenging concept and a multi-step procedure (such as solving osmosis problems), it is now possible to scaffold toward mastering this type of problem.

a. Highlight the water labels in blue and solute labels in green.

b. Draw an arrow from the larger (blue) water value toward the lower (blue) water value. If both solute and water percentages are given, then this will be simple. If only one or the other value is given, subtract the value from 100 to determine the missing value. For example, if you only know that there is 45% water inside the cell, then 100-45=55. There must be 55% solute inside the cell since they both comprise the total solution.

c. Predict whether the cell will expand (take on water), shrink (lose water), or remain the same.

d. Look at the (green) solute value.

If the solute is greater on the outside of the cell, then label the system as "hypertonic".

If the solute is less on the outside of the cell, then label the system as "hypertonic".

If the values are equal on both sides of the membrane, then label the system as "isotonic".

Using the four-step process previously described, I model how to solve each style of problem. 

I use the "I/We/You" technique to assist students to complete the Osmosis Worksheet. Students are to number each problem (#1-3 top row, left to right, #4-6 middle row, left to right, etc. for both sides; a total of 18 problems).

In this technique, the responsibility passes from teacher to student (like the Russell Wilson (QB)- Marshawn Lynch (Running Back) hand-off). Don't judge me, now. I bleed Seahawk green and blue!

"I" will work the four-step process for problem #1. Then I call on a student to help me answer #2. I will do the problem solving but she will assist as I feign that I don't remember how to do it. Then, I will kick it out to all students to work on the next two only (so that they will have completed four). As they do so I will circulate to assist.

3) Predict-Observe-Explain (Part #2 of 2)

Students are to return to their lab stations and Petri dishes that have been soaking over the past 25 minutes. Based on the firmness of the control group potato, they are to determine if the potato gained water (became more firm) or lost water (became less firm). Record observations and explain what happened by correctly using these terms: concentration, concentration gradient, osmosis, and solute.

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

5 minutes

"Cold Call": This technique comes from the treasure chest of Doug Lemov's seminal book, Teach Like a Champion (TLAC). The process works something like this:

According to the following excerpt taken from a TLAC blog, "In order to make engaged participation the expectation, call on students regardless of whether they have raised their hands." The blog asserts that teachers ought to pay attention to four "key principles to Cold Calling: Predictable, Systematic, Positive, and Scaffolded."

In other words, calling on students is a habitual event in a class session, there is pre-meditation in terms of who is asked, where the questions are directed in a classroom, and is not used to single out particular students (e.g. teacher's pet). Furthermore, it is not used a punishment but is an opportunity for students to get it right and feel great about it! Lastly, simply questions lead to more complex questions.

In the context of my lesson, I use cold call to ask students to define the following terms: hypotonic, isotonic, hypertonic. Next, I ask a student to predict the flow of water based on a given scenario (similar to what students were working on in class earlier).

Please click here to link to the next lesson in the series.