Lesson 3 Text Selection – Section 7.4 (pp. 201-207) Cellular Transport Lesson 3 Text Selection – Section 7.4 (pp. 201-207)

Objectives: At the conclusion of this lesson students should be able to: Explain the processes of diffusion, facilitated diffusion, osmosis, and active transport. Identify dynamic equilibrium in a diffusion demonstration. Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell. Discuss how large particles enter and exit cells.

Predict Food coloring demonstration Drops of red and blue food coloring are added to opposite ends of a container of water. What will happen when the food colorings are added? What will happen a few minutes later?

Brownian Motion Substances dissolved in water (solutes) move constantly in random motion Causes diffusion net movement of particles from an area where there are many particles of the substance to an area where there are few particles of the substance How can you tell this is happening/has happened in our experiment?

Observe & Hypothesize What happened to our food colorings? How can this result be explained? Figure 7.20 © Glencoe-McGraw Hill (2007)

Dynamic Equilibrium Once a uniform purple color is reached, the food coloring particles continue to move randomly. However, at some point, all particles of a substance (in this case food coloring) will be as spread out as they can and there will no longer be areas of high and low concentration. When this occurs, dynamic equilibrium has been reached.

Factors that Affect Diffusion This looks like a multiple choice question! Three main factors affect the rate (speed) of diffusion: Concentration of the diffusing particles Temperature Pressure If any of these three increases, the diffusion rate will increase. Why? Set up some demonstrations to show students these: 1.) Add differing amounts of food coloring to two beakers to see how fast diffusion occurs in each. 2.) Place food coloring in a beaker of boiling water. 3.) Place food coloring into the bottom of a 2-liter bottle that is under pressure/ or use vacuum to reduce pressure.

Transport Processes Passive transport – movement of a substance across the plasma membrane without the use of the cell’s energy. Active transport – requires the use of the cell’s energy to move substances into or out of a cell across the cell membrane. No Energy Required Requires Energy

Facilitated Diffusion Water can diffuse easily across the plasma membrane – most other substances cannot. In facilitated diffusion, special transport proteins move ions and small molecules across the plasma membrane Click here for video Figure 7.21 © Glencoe-McGraw Hill (2007)

Osmosis The diffusion of water across a selectively permeable membrane. Cells must regulate this in order to maintain homeostasis. One of three situations exists. Figure 7.22 © Glencoe-McGraw Hill (2007)

Isotonic Solution Cell is in a solution that has the same concentration of water and solutes Iso – Greek meaning “equal” cell is in dynamic equilibrium with environment Water enters and leaves the cell at the same rate. Figure 7.23 © Glencoe-McGraw Hill (2007)

Hypotonic Solution Cell is in a solution that has a lower concentration of solute than the cell hypo – Greek meaning “under” Net movement of water is into the cell Causes osmotic pressure In animals – cell could burst In plants, cell wall prevents bursting; cell becomes firmer Figure 7.24 © Glencoe-McGraw Hill (2007)

Hypertonic Solution Cell is in a solution that has a higher concentration of solute than the cell. hyper – Greek meaning “above” Net movement of water is out of the cell Results: In animals – cells shrivel In plants, central vacuole pulls away from cell wall; plant wilts Figure 7.25 © Glencoe-McGraw Hill (2007)

Red Blood Cells – A Comparison Is your blood pure water? What would happen to your red blood cells if pure water were to be injected into your blood stream?

Homework Reread pp. 201-207 Complete the Section 7.4 Study Guide

Concentration Gradient Active Transport Requires the cell’s energy Moves substances across the plasma membrane against a concentration gradient. Concentration Gradient Active Transport Passive Transport Amount of a substance

Carrier Proteins commonly called pumps Click here for video Figure 7.26 © Glencoe-McGraw Hill (2007)

Na+/K+ ATPase pump Enzyme that uses cellular energy to pump 3 Na+ out of the cell and 2 K+ into the cell. Figure 7.27 © Glencoe-McGraw Hill (2007) Click here for video

Coupled Transport The sodium-potassium ATPase pump sets up concentration gradients of these two ions across the plasma membrane. Other substances can use this gradient to get into the cell through a process called coupled transport. Figure 7.28 © Glencoe-McGraw Hill (2007)

Transport of Large Particles Used for substances that are too large to move through the plasma membrane by diffusion or carrier proteins. Endocytosis – process by which a cell surrounds a substance with its plasma membrane and brings it inside. Exocytosis – process by which vesicles fuse with the plasma membrane and secrete their contents outside the cell. Used for expelling waste Secreting cell products (i.e tears, hormones) Figure 7.29 © Glencoe-McGraw Hill (2007)

Homework Complete the Transport through Membranes worksheet Study for QUIZ on Tuesday. You should be able to: Match terms with their definitions Draw a plasma membrane and label its parts Identify the tonicity of a solution and explain its effect on a cell. Read a short passage and explain what cellular transport mechanisms (diffusion, osmosis, etc.) are occurring and why.