In and Out of Cells Day 2
Lesson 11 of 18
Objective: Students will be able to explain how solutes and other materials move across membranes.
The Cell Processes unit is part 2 of my Cells 'R Us project based learning experience. Once the students are familiar with the structure of cells, we move on to how cells work. The lessons in this sequence are based on the "need to know's" created by the students (with guidance) for the Cells 'R Us project.
The complete sequence I use for the Cells 'R Us project is:
I tell the students that today we will see what happened to the eggs over night (In and Out of Cells Day 1), but before we do that, I would like them to make a hypothesis about the results based on what they now know about the different solutions and how materials move across membranes.
I distribute the Movement Across Membranes Day 2 sheet, and direct the students to think about and discuss their answers to items 1 and 2 before writing them down (first page). I don't show the eggs right away to encourage discussion with peers (SP8 Obtaining, Evaluating, and Communicating Information).
Once students have finished their hypothesis, I bring out the jars that contain the naked eggs. I tell the students that this is a demonstration, so I will be lifting the eggs one by one and give them ample time to record their observations. They will not draw conclusions (yet), but rather I want them to focus on what they can see. I hand out a "Says-Means-Matters" sheet.
Note to Teachers: I adopted the Says-Means-Matters strategy after I taught this lesson, so the students did not get the sheet until day 3 in this series, when they recorded observations for that day. When I teach this lesson again, this is where I plan to give out the sheet and guide students through it.
As I lift each egg up from the solution, I make sure that every student can see and call students to come up for closer inspection as needed. Students that come up are instructed to state what they see using as many descriptive words as possible. Before placing the egg back in its solution, I also weigh it and record this new weight on the side of the container.
Once observations are done, I tell the students to discuss what they saw (SP4: Analyze and Interpret Data) continue to work on their Movement Across Membranes Day 2 sheet. Their conclusions (item 4) must be defended using the ACE strategy (SP7: Engaging in Argument from Evidence) in preparation for a class discussion.
The discussion that follows gives students an opportunity to defend their explanations based on solid data (NGSS Practice 7: Engage in argument from evidence) and evaluate the validity of the findings of others (NGSS Practice 8: Obtain, evaluate and communicate information).
Once the discussion is done, I call their attention to the fact that they will be testing a solution of their choice on the next day. They must reach a consensus on what solution they want to test, why, and are responsible for bringing it to class.
To close this lesson, I ask the students to write a a post-it note that includes:
- One thing you learned.
- One thing that was surprising.
- The liquid they chose and what they expect will happen to an egg soaked in that liquid.