## Reflection: Checks for Understanding Water on the Move: Osmosis (#1 of 3) - Section 3: Instructional Input/Student Activities

Guiding Questions/Decision Tree:

1. What is the water % inside and outside the cell? Are they equal?

2a. If yes, then there is no net movement of water and no real change to the cell system.

2b. If no, then from which direction must the water move to reach equilibrium (out -> in or in -> out)? How much water must move to reach EQ? Student B has jotted down the trick to know what EQ is at the top of the paper. Just one of several viable techniques.

ERROR CHECK: For problem 1-2 (Row #1, beaker #2) the EQ value is not correctly calculated. The total difference between external, internal water is 50%, half of it remains on the outside leading to a proper EQ of 40+25% or 90-25% = 65%. More is needed than simply writing out the formula, huh?

3. What is the physical effect of the cell (shrinks, expands, stays the same)? Student A correctly identifies these but B fails to do any! Student B is a very good student but she must have rushed through it. Success has no shortcuts!

4. Looking at the solute concentration outside the cell, what label applies (hypertonic= more solutes; hypotonic= fewer solutes; isotonic=equal amount)

You can see that both students completed their problem sets by correctly answering all four aspects of the problem solution. And this all started with a basic understanding of the concentration gradient, and adding the concepts of solutes, solvents, and solutions with the goal of reaching equilibrium. Essentially scaffolding from simple (initially known) to more complex (initially unknown).

Student A Osmosis Problems

Student B Osmosis Problems

Checks for Understanding: Osmosis is simple if you just understand diffusion!

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

Unit 2: 2) Cells ("Form and Function")
Lesson 14 of 20

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

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Standards:
Subject(s):
Science, diffusion, cells, form vs. function, Osmosis, Concentration Gradient, permeability, models, cell transport, hierachical organization, scientific conclusions
60 minutes

### Mitchell Smith

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