Egg-citing Cell Adventures - Movement Across The Membrane

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SWBAT create a model that compares the animal cell to an egg and predict the effect varying solutions will have on the movement across the cell membrane. Students are introduced to the concepts of osmosis and diffusion in order to maintain homeostasis in the cell.

Big Idea

This lesson will "egg" on your students to get excited about cells as they discover more about movement across the cell membrane with the processes of osmosis and diffusion!

Hook - Egg-nalogies of Cells

5 minutes

Using students' prior knowledge from the lesson on cell organelles, students will respond to the following prompt:

  • The animal cell is like an egg.  Be creative and cite as many pieces of evidence to support or refute this statement.

Students are also encouraged to draw a basic diagram of the animal cell and the egg to create a visual side-by-side comparison to support their stance.  

By making the opening prompt of this lesson a statement that must be evaluated by the students, students are able to activate their prior understanding and incorporate their writing skills to develop a claim and provide evidence to support their stance.  This open-ended brief writing assignment engages student creativity in a more rigorous manner, rather than a simple yes or no question.    

Sample of Student Work: Egg Analogy - Students seemed to relate to this analogy and were able to build their understanding on this very simple comparison.


Direct Instruction - Unscrambling Student Understanding

35 minutes

Due to the detailed structure and complex functions that occur to enable movement across the cell membrane, the teacher will dedicate a majority of this lesson to introduce and reinforce the details of cell membrane structure, as well as the processes of osmosis and diffusion.  TheseLecture Notes - Cell Membranewill introduce students to the features of the cell membrane and incorporate the organic molecules that were studies in prior lessons, such as the individual lessons that each focused on proteins, carbohydrates and lipids.  

It is essential for students to have a strong comprehension of the cell membrane composition to truly understand cellular function as the class progresses in their cell biology curriculum!

This lesson consists mostly of teacher-led direct instruction.  If you feel that your students do not need the intense content delivery for an extended time, you may want to compress the lecture notes and combine with the next lesson: In&Out to best meet the academic needs of your student population.  

Common Student Misconceptions and How To Avoid the Pitfalls:

  • All materials that come in contact with the cell can enter the cell.  Students need additional support in understanding that size and chemical composition of the molecule will determine if the substance is allowed to pass through the selectively-permeable cell membrane and enter into the cell.  
  • The cell membrane is a thin, simple structure.  So often, students and teachers alike, draw the cell membrane as a simple line which causes confusion that the cell membrane is actually a phospholipid bilayer consisting of lipids, proteins, and carbohydrates.
  • Cell movement always goes in the direction of high concentration to low concentration.  Students need additional support in understanding active transport and how molecules from areas of low concentration to high concentration.  Active transport also requires cell energy in the form of ATP.  This concept is when most students become overwhelmed and need to simplify movement across the cell membrane.
  • Osmosis and Diffusion are the same thing.  Students need to understand that diffusion is the movement of any molecule from an area of high concentration to an area of low concentration.  I demonstrate this by spraying flowery body spray around the classroom until all students can smell the scent.  (plus it makes my room smell good!)  It is important to emphasize that osmosis is the movement of WATER across a selectively permeable membrane and that osmosis is only used to describe the movement of water!
  • The cell membrane passes materials through at random times.  The cell's functions are directly related to the effort to maintain homeostasis.  Movement across the cell membrane is directly related to the cell's desire to maintain homeostasis as it moves molecules across the membrane to bring in necessary materials and remove cellular waste.

Guided Practice - Egg-celent Model of Movement Across the Membrane

10 minutes

Students will watch the video below to reinforce the Lecture Notes - Cell Membrane that describe the movement into and out of the cell.  This video provides a visual model of the interaction of cells in hypertonic, hypotonic, and isotonic solutions.  Students are encouraged to take notes during the video so they have evidence from the Naked Egg Lab to develop a narration that explains the interaction of cells in each of the these three types of environments.  

 At the conclusion of the video, students will use their video notes and Lecture Notes - Cell Membrane to develop a narration that describes the movement of molecules when a cell (or naked egg) is placed in a hypertonic, hypotonic, or isotonic solution.  Students will need to draw a model of the movement of molecules across the cell membrane to depict molecules moving into, out of, or both into and out of the cell.  

Once complete students will share their narrations in their lab groups of 3-4 students to ensure the details of each student's narration is accurate and reflects the information provided in the lecture notes.

Sample of Student Response #1: Using the egg as an analogy for a cell simplified the process and supported all students to understand the process of moving material into and out of the cell.

Sample of Student Response #2: This sample provided great details and demonstrates a strong understanding of the concept.

Close - Eggs-amining Osmosis

5 minutes

As a close to the lesson, students will create their own definitions that differentiate the process of osmosis and diffusion.  Students are encouraged to use their own wording and not just copy their lecture notes or textbook.  Students will also provide evidence from  the gummy bear or egg examples that were provided during the lesson.

Once students have finalized their definitions with examples for both terms, they will turn to their neighbor to share their newly drafted definitions.  Students will collaborate to determine if the definitions and examples are accurate and appropriate for this activity.  

Sample of Student Response - This student used their experiences in the lesson to develop an original definition of the terms osmosis and diffusion.

Students will complete Reinforcing Activity: Movement Across the Membrane as homework to practice the concepts that were introduced in today's lesson.