Cell Transport Classroom PPT

Cell Transport ACTIVATE PRIOR KNOWLEDGE – CELL ANALOGY • Read the analogy of the cell as a nation in Think About It and discuss ways materials might enter and leave a country. MYSTERY CLUE – DEATH BY…WATER? As Michelle ran, she perspired, losing salts from her bloodstream. And as she drank more and more water during the race, the concentration of dissolved salts and minerals in her bloodstream decreased. How do you think these phenomena contributed to Michelle’s condition? • What do we already know about the cell membrane? • • Skim the first four pages of this lesson. What characteristic of a cell membrane might have contributed to Michelle’s problem? • The difference in salt concentration inside and outside the red blood cells caused excessive water to enter the cells. BUILD VOCABULARY Diffusion: The process by which particles tend to move from an area where they are more concentrated to an area where they are less concentrated. Facilitated Diffusion: The process of diffusion in which molecules pass across the membrane through cell membrane channels. Osmosis: The diffusion of water through a selectively permeable membrane. • • The word facilitate means “to help.” In facilitated diffusion, protein channels facilitate the diffusion of large molecules across the membrane. USE VISUALS – DIFFUSION • Some materials, such as oxygen, diffuse across the cell membrane, without using energy, while others require energy to pass through. • • • • • • How do the first and second drawings differ? CBR – The first shows a higher concentration of a solute outside than inside a cell. The second shows a greater number of molecules moving in than moving out, as indicated by more arrows pointing in than out. How do you know equilibrium has been reached in the third illustration? How do you know equilibrium has been reached in the third illustration? CBR – There are equal numbers of molecules on both sides of the membrane, and the arrows show about the same number of molecules moving in and out. Equilibrium does not mean that movement stops; rather it continues to both directions, and the same concentration is maintained on both sides of the membrane. USE VISUALS – DIFFERENTIATED INSTRUCTION • • • Concentration has multiple meanings in English. One correct definition of concentration is “directed effort or attention.” The scientific meaning of concentration refers to the relative amount of one substance in another, for example, the concentration of salt in water. FIGURE 7-15 – DIFFUSION • • • • • Predict - How would the movement of solute particles seen here be different if the initial area of high concentration had been on the inside of the cell instead of the outside? Rephrased – What would be different if the high concentration had been inside the cell to start with? CBR – If the concentration of solute particles had been higher on the inside of the cell, more solute particles would have moved out of the cell than into the cell. Explain how you can demonstrate diffusion by spraying air freshener in a large room. CBR – Answers should reflect an understanding that in diffusion, molecules move randomly from an area where they are more concentrated to areas where they are less concentrated. So, when air freshener is sprayed in a room, the smell will diffuse from its point of origin until it can be detected everywhere. BIOLOGY IN-DEPTH – RATE OF FACILITATED DIFFUSION In simple diffusion, concentration is the only factor that affects rate. In facilitated diffusion, the rate also depends upon the number of specific carrier protein molecules in the membrane, because the diffusing molecules can move across the membrane only through those proteins. An example is the diffusion of glucose into cells. Such diffusion occurs most of the time as facilitated diffusion. No matter how much the cell “needs” glucose or how great the difference in concentration is between the inside and outside of the cell, the rate at which the glucose can diffuse into the cell has a limit because of the limited number of glucose carrier protein molecules in the lipid bilayer. USE VISUALS – OSMOSIS • • What happens to the concentrations on each side of the membrane as water diffuses through? CBR – The concentrations change until they reach equilibrium.