Lesson Topic: Understanding the Cell Membrane Grade level: 7th Length of lesson: 45 minutes *** REVISED****

Transcription

1 Lesson Topic: Understanding the Cell Membrane Grade level: 7th Length of lesson: 45 minutes *** REVISED**** Stage 1 Desired Results Content Standard(s): Life Science Grade 7 A. Cells The student will recognize that specialized cells in multi-cellular organisms perform specialized functions. Understanding (s)/goals Students will understand: Properties of cell membranes and how they transport materials in and out of a cell. Student objectives (outcomes): Students will be able to: Essential Question(s): How does a molecule get into a cell? What is the difference between diffusion and osmosis What is the difference between active and passive transport 1) Define diffusion, osmosis, active transport and passive transport. 2) Differentiate between the major types of cell membrane transport. 3) Demonstrate there understanding of active and passive transport in a short activity. Performance Task(s): 1) Students will do a mini-demonstration to practice active and passive transport. 2) Students will participate in a group discussion about two other demonstrations that I will do in class. Stage 2 Assessment Evidence Other Evidence: Do a worksheet on the types of cell membrane transport for homework. Informal assessment from students through class discussion. Preparation: Stage 3 Learning Plan Set-up stations of materials for diffusion lab Cornstarch, iodine droppers and tablespoons at the demo table 1 station of resalable plastic bags 1 station of big cups/beakers Set-up materials for potato demonstration on small front table potato, dishes, knife, salt Set-up materials for car demonstration behind/underneath counter car, shoebox Introduction: Begin with students thinking about diffusion, what do you know so far from other science classes? Body:

2 Begin with 2 volunteers for potato demonstration- 1 cuts the potato, 1 makes the depressions, 1 puts water on the bottom of the dishes, 1 puts salt in one the depression Hypothesize the demonstration Draw diagram on board What affect will the salt have? Will the water level rise or fall in each dish? Begin discussion about what diffusion is- Key Questions build off students answers What do you know about diffusion so far? Where does diffusion occur in the cell? What are some properties of diffusion? Draw students knowledge on the board Diffusion Figures Kinesthetic Activity Students act like molecules Have all the kids around one table in the classroom, they have to be touching Q- What do you do as molecules need to do to be comfortable? Before there was a high concentration of students around the table, to move away is to move to lower concentration. Diffusion Lab do w/ students Pick 4 volunteers Q From the materials, which of these is going to be our membrane? What are going to be our molecules that are going to diffuse? 1 students puts the starch in the plastic bag 1 students fills that bag with water 1 students rinses off the bag to avoid any errors 1 students fills the cup with water 1 have students tell me how much iodine to add Hypothesize what will happen in diffusion lab- make data table and have students fill it in Draw diagram on the board, talk about which way the molecule will or will not diffuse. Check understanding of diffusion Selectively permeable membrane- Read section out loud in the book pg 41 Students give examples about what a selectively permeable membrane is in there lives. Draw diagram on the board Students get to vote on which shape goes threw the selectively permeable membrane. 1 student draws diagram after elapsed time. Major transition diffusion > selectively permeable membrane -> osmosis Read about osmosis pg 43 Give 2 major characteristics of osmosis that are added to the basic concepts of diffusion Concentration of water, selectively permeable membrane Example Gummi Bear Lab why did the gummy bear expand? Go back to salty potatoes What happened, where did the water in the whole come from, where was the high concentration of water, where was the low concentration of water, what

3 was the selectively permeable membrane? Check understanding of osmosis Group discussion -What if a molecule needs to go from low concentration to high concentration? What does the molecule need? Active transport - Refer to page 44 Passive transport diffusion Active transport require energy, transport proteins Car demonstration List materials; have students in groups figure out how to get Johnnie the tractor get to the top of the shoebox? Listen to different ideas, have one group show there idea Go back to diffusion demo Color change? Why? What diffused in which way? Finish filling in data table Learning Activities: Diffusion- Materials: Tablespoon, cornstarch, two cups, water, resalable plastic bags, plastic dropper, iodine, beakers Time: 15 minutes To demonstrate diffusion through a semi permeable membrane, stir a tablespoon of cornstarch into half a cup of water and pour the mix into a plastic bag. Seal the bag, rinse off to remove any cornstarch, and place it in a clean cup full of plain water. Add 20 drops of iodine to the water in the cup. Later, show students the cup and ask: Why did the water in the bag turn purple? ANSWER: Iodine molecules passed through the plastic into the bag and interacted with the cornstarch. Why didn t the water in the cup turn purple? ANSWER: Starch molecules were too big to pass through the bag Osmosis- Materials: Raw potato, knife, 2 shallow dishes, tap water, salt Time: 5 minutes in the beginning of class, 10 minutes at the end of class Use a potato to demonstrate the process of osmosis. At the beginning of class,

4 cut the raw potato in half & hallow out a small depression in the curved side of each half. Place the halves flat side down in the shallow dishes containing a small amount of tap water. Place a pinch of salt in the depression of one potato halves and set aside. At the end, go around to each group and have the students observe what happened? ANSWER: Depression without salt had become dried out and the depression with salt has filled with water. Where did the water in the depression come from? ANSWER: Water moved by osmosis from an area of higher concentration in the potato cells to an area of lower concentration in depression containing salt. Active & Passive Transport- Materials: Small board, stack of books, toy car Time: 5 minutes Challenge the students to model active and passive transport using the materials. The board should lean against the stack of books and the car going down hill should represent passive transport and the car going up the hill should represent active transport. Why do you need to supply energy to move the toy car up the ramp? ANSWER: Overcome gravity Why is energy needed to actively transport some substances into a cell? ANSWER: Move substance from lower concentration to higher concentration Conclusion: Students will use there new and past knowledge to compare and contrast diffusion concepts What is the difference between diffusion and osmosis? What are the two key differences? What is a selectively permeable membrane? What is the difference between active and passive transport?

5 References: The Biology Project Cell Biology. Cell Membrane Tutorial. General Biology Program for Science Teachers Diffusion, Osmosis and Cell Membranes. Science Explorer. Cells and Heredity. Chapter 1 Section 4 The cell in it s Environment pp