Lesson 9 of 12
Objective: Students will be able to develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.
In this lesson, students practice critical reading strategies. The teacher models how students can use the NGSS Crosscutting Concepts to help guide their thoughts when they read. Students use these reading strategies as they interact with a text about diffusion and cell transport. Then, students use eggs to model diffusion and osmosis in cells.
This lesson is specifically designed to address the following NGSS and Common Core Standards:
MS-LS1-2 Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.
CCSS.ELA-LITERACY.RST.6-8.10 By the end of grade 8, read and comprehend science/technical texts in the grades 6-8 text complexity band independently and proficiently.
Scientific and Engineering Practices:
Asking Questions and Defining Problems (SP1): Students at any grade level should be able to ask questions of each other about the texts they read.
Developing and Using Models (SP2): Develop a model to describe unobservable mechanisms.
Systems and System Models: Models can be used to represent systems and their interactions—such as inputs, processes and outputs—and energy, matter, and information flows within systems.
Stability and Change: Systems in dynamic equilibrium are stable due to a balance of feedback mechanisms.
While I specifically addressed "Systems and System Models" and "Stability and Change" above, this lesson really connects to every NGSS Crosscutting Concept as students draw connections to each as they read.
Begin class by asking, "What are you going to learn today?". Students should respond by referring to the Essential Question, "How do cells contribute to the function of living organisms?". This EQ can be referenced both on my front board as well as in their Cells Unit Plan.
Have students get out their Cells Unit Plan. Explain that their focus of this particular lesson is Skill 3 (I can create a model that shows the relationship between cell structure and function) and Skill 4 (I can identify important materials and processes that are required for cells to function). Have students read the skill and self-assess where they stand in their level of mastery in this skill. Students rank themselves on a scale of 1 to 4 (4 being mastery).
As the unit moves forward, I have the students continually self-assess on each skill. In my class, this will be the students' second self-assessment, so they change their scores if they feel that their learning has improved. Check out the student's unit plan below to see how students update their mastery level with each lesson.
For middle school students, thinking critically during reading is a challenging task. However, being able to think beyond the text is key to real understanding of scientific concepts. I have found that the NGSS has provided us with an invaluable tool in the Crosscutting Concepts. These provide students with themes that can guide their critical thinking. When students in my class read, they document what they are thinking as they "talk to the text." While we have done this on many occasions, I find that it is important to return to strategies and model them again. Although I have modeled this strategy in the past, this extra opportunity for students to watch me model reading strategies still provides many benefits.
In the video below, I model reading strategies as I read the first page of the Cell Transport Reading. There are a few key things to note about the video:
1. As I model reading strategies, I explain what I am thinking as I am reading. It is imperative to realize that the "thoughts" I share are strategic. Each connects to one of the NGSS Crosscutting Concepts. However, as I ask the students to make the connections at the end of this mini lesson, I do not explicitly state which concept I am connecting to. Prior to the lesson, I type out these connections to the reading and crosscutting concepts in a document I will have the students refer to later.
2. The reading I use is something I wrote. It is definitely in my voice. Whether you use this reading or a different article that you have, the strategies I am sharing will work on any text!
3. It is long. I considered shortening it, but I thought I would include it in its entirety if you weren't completely familiar with all of the NGSS Crosscutting Concepts.
After modeling, I provide the students with the "Cell Transport Teacher Discourse Examples". This is a document that lists the discourse comments I used when I was modeling. I have each table group reference their Matrix Of Crosscutting Concepts and discuss which crosscutting concept each comment connects to. Then, each table group shares the crosscutting concept connection to my modeling statements.
Students often identify the following NGSS Crosscutting Concept Connections:
Patterns (Sometimes students say "Stability and Change"): High to low…I have heard that before. I know that wind is when air moves from areas of high pressure to areas of low pressure.
Stability and Change: Things in the world want to reach stability. Like heat transfers from an object that is hotter to an object that is cooler.
Scale, Proportion, and Quantity: Could we measure change the concentration and measure how that changes the rate of diffusion? Would that relationship be linear?
Matter and Energy: Cells go through chemical reactions. The matter would be conserved during those reactions.
System and System Models (Sometimes students say "Cause and Effect"): If we changed the amount of oxygen that could enter a cell, how would that affect the system (cell)?
Structure and Function: Membranes have tiny gaps. I wonder how the structure of the cell membrane helps with the function of diffusion.
It is important to note that many of these comments could "fit" into multiple concept categories. This can lead to a great discussion about how there are themes in science that interconnect and overlap.
**When students in my class read and "talk to the text", they use what I call The Ladder of Discourse. Just in case you were interested in utilizing this strategy in the future, I have included all of the related resources for implementing this strategy.
After removing the egg shell, eggs provide a great opportunity for students to see diffusion first hand. Over the course of days, students place the eggs in water, food coloring, and corn syrup as they measure the change in mass to provide evidence of cell transport.
Teacher Tips for Planning and Preparation:
1. Prior to this lab, soak eggs in vinegar for 2 to 3 days. The number of eggs will depend on the number of groups you have. You will need to soak extra eggs as some will break over the course of the lab.
2. On the first day, students will need to gently rub the shell off of the egg. In order to prevent eggs from breaking, I let students know that if there is a part of the shell that is still hard, they should leave it and not attempt to pick it off. As shown in the picture below, sometimes there is a small section that is not submerged in the vinegar when the egg floats that does not come off the egg. The experiment will still work great!
3. This lab takes multiple days to complete, but will only require about 10 to 15 minutes each day. Thus, you should plan on carrying out other lessons with the remainder of the class. In my Cells Unit here on BetterLesson, the lessons that follow this one are the ones that I complete simultaneously with this egg lab. Each of these lessons build on the same reading and carry through the idea of cell transport, diffusion, and the NGSS Crosscutting Concepts. These lessons include Membrane Mania and pHun with Phenolphthalein.
These lessons also play a role in developing the students understanding as we move through this lab over a course of days. When looking at the lab questions in the student document, some of the questions I ask require the students to have developed their knowledge of transport further in these lessons. For example, in Membrane Mania, students develop and understanding of active and passive transport. In pHun with Phenolphalein, students develop an understanding of the importance of surface area to volume ratio.
By the time students finish the egg lab, they will have been given instruction in these areas; thus, there are questions about active and passive transport as well as surface area to volume ratio in this lab document.
Provide students with the procedure and student document for "Eggsellent Eggsperiment" and have them follow the procedure. Each day be sure to talk with groups about their data, evidence of diffusion and osmosis, and the importance of cell transport in cells. It is important to use these conversations to formatively assess if students are connecting the this model to transport in cells.
It is important to keep in mind that the big idea and target of this lesson is that students connect to the idea that cells require molecules to move in and out of cells in order to go through important reactions and processes that allow cells to function. After each day, have students discuss in their groups in order to make these connections. Some questions you could discuss in small group and as a class each day include:
- This egg serves as a model of transport through a membrane in cells. Why is cell transport important?
- What are some reactions important for cell function that would require transport?
- What are some important materials that might have to move across the cell membrane (both in and out) in cells?
- What would happen if cells could not go through transport like diffusion and osmosis?
Without making the deliberate effort to have the students connect to the big idea, middle school students get wrapped up in how "cool" the egg looks and, in their excitement, can miss the scientific concept this model is designed to help them understand.
Have students complete the formative assessment/exit ticket to make sure that students are connecting to the big picture and the importance of cell transport. After students complete the formative assessment, I sort the student work into piles of similar learners. Then, in an upcoming lesson, I meet with these groups to address specific student needs.
In this first example, the student identifies cellular respiration as a process that would require transport. It is key that she actually names specific molecules needed for the reaction and states that it is a reaction that takes place in cells.
In the second example, the student recognizes that waste must be removes from cell and transport allows this to happen.
When sorting student work into groups of similar learners based on this formative assessment, I typically find there a few common groups:
1. Students that list the types of transport but do not explain their importance. The students might write something like "Diffusion, osmosis and active transport allow cells to live." These students are not connecting to the idea that these processes are important because they move important materials required for reactions in cells. With these groups it is important to show them examples of how transport is important in processes such as photosynthesis and cellular respiration.
2. Students that explain that transport is important because it allows important materials to enter and exit the cell that are required for cell function but do not give any specific examples of the molecules or reactions (Student Example #2 Above).
3. Students that include great examples and reactions, but do not explicitly state that transport occurs when materials enter and exit the cell. I find that some middle school students have a "one track mind". Either they only picture diffusion allowing materials to enter the cell (most common in students) or they only picture waste and materials leaving the cell (less common students). For example, in the second student example above, it would be important for me to meet with that student to find out if they only picture transport as waste removal or if they understand that transport of materials occurs when materials enter and exit the cell and they just happened to include an example of waste exiting the cell.