In and Out of Cells Day 1
Lesson 10 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:
For this lesson series, you will need 14+ pasteurized eggs with the shell removed. To remove the shell, place the eggs in a bowl and cover them completely with vinegar. Allow them to rest overnight.
Under gently running water, gently rub the shells off the eggs leaving just the cell membrane. You will only need four of the naked eggs for this lesson. You will need one egg per group on the following lesson - in my case that is 7 eggs.
The extra eggs are to allow for breakage when removing the shells.
You will also need:
One copy of the "Movement Across Membranes worksheet" per student.
Four 250 ml beakers (or jars) labeled A, B, C and D:
- A - contains 150+ ml of plain water
- B - contains 150+ ml of clear corn syrup
- C - contains 150+ ml of saturated salt solution (stir as much salt into the water as you can)
- D - contains 150+ ml of vinegar (control)
To start the lesson, I ask the students to get into their Cells 'R Us project groups, and add to/look over their plan. By now, they should already have identified some of the main buildings in their amusement park attractions, as well as be able to describe how their attraction obtains energy. I tell the students to Think-Pair-Share in response to, "How do people and resources come in to/leave a zoo/movie theater/mall?". Once we have a couple of ideas on the board, I ask the students to think about how a cell might carry out that same process.
I then tell the students that our purpose for the next couple of days is to identify different ways in which cells can bring materials in and remove waste. I also tell them that once they have some basic information on just how this happens they will be using what they learned to plan and carry out their own investigation (SP3 Planning and Carrying Out Investigations) involving the transport of materials across the cell membrane.
I then ask, "What would we need in order to try to plan an investigation around this question?" The students usually fail to mention the fact that we need a membrane, and won't know to ask specifically for a permeable membrane, however, this is the time to remind them that cells have membranes, and that they already actually possess some knowledge about them. During this conversation I also briefly introduce the concepts of diffusion and osmosis. At this point I just provide the words and examples, such as, "Diffusion is what happens when your mom is making brownies. As soon as you smell them, you run to the kitchen. Who smelled them first, you or your mom?" or, "Osmosis is how the roots of a plant take in water."
I show the students the "naked" eggs (pointing out the membrane and explaining how I removed the shell). I weigh each egg, recording the weight on the side of its container and make a big production of placing one egg into each of the 4 prepared jars (see teacher preparation). I tell the students that we will keep these eggs in the jars overnight to see what happens. Throughout the demo, I ask questions directed not only at ensuring that students are understanding what I am doing, but also at eliciting their hypothesis and identification of variable (SP1 Asking Questions and Defining Problems).
Once the eggs are in their beakers, I have students pick up the "Movement across Membranes" sheet. I tell them that they will be working on the sheet in pairs, and that through their answers they will be telling me what they know or can find out through their own research.
I tell them that the main source of information for them to use today is the cell transport website I created specifically for them, knowing how they like interactives and visuals, although they can also use their textbook. I also tell them that I will set a timer for eight minute intervals so that they are aware of how much time has passed, and that by fourth bell, they must be ready to share their understanding through the ACE'd explanations they crafted in their sheet. (student work 1, student work 2, student work 3)
As the students are working, I walk the room clarifying concepts, and asking the students to explain each of the concepts to their tables or to a table that might be struggling. I am also taking notes and informing particular students that in our closure they will be "called on" to explain one of the big ideas. (SP8 Obtaining, Evaluating, and Communicating Information). I try to incorporate as much peer-led facilitation of concepts in order to give students the opportunity to engage in discussions with peers and communicate their understanding of science effectively.
Ten minutes before the period ends, I reconvene the class using the call and response strategy. I write the words diffusion, osmosis, and active transport on the board and invite the previously selected students (see Explore) to explain their understanding of each term as I scribe for them.
In each case, I invite the rest of the class to add on to what was said, as well as ask clarifying questions. The goal is for all students to have an opportunity to share.
The exit ticket for the day is a response to the following questions:
- What was the most difficult concept in today's lesson?
- Knowing that you will use that difficult concept in the coming lessons, what is your plan to review it?
By giving students a chance to think about what they need to do to prepare for a lesson, I am shifting the responsibility for the learning from the teacher to the students.