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TACM-2-Concentration of Solutions

Page history last edited by Jay 14 years, 10 months ago

TODAY'S OBECTIVES

Student can...

  • Students correctly use vocabulary from textbook section 7.3 (phospholipid bilayer, hydrophobic, hydrophilic, concentration, diffusion, osmosis, concentration gradient, solution, solute, solvent, volume, isotonic, hypertonic, hypotonic, net movement, equilibrium; later-facilitated diffusion, simple diffusion, active transport, endocytosis, phagocytosis, exocytosis]
  • Students correctly understand and use symbols like [ ] to represent "concentration"
  • Explain solute or solvent movement across a membrane based on descriptions of concentration.
  • Student identify, understand and articulate the difference between "quantity" and "concentration" [eg. 1 L of fluid may have more Na ions in it than a blood cell but the 1 L can still have a smaller concentration of Na than a cell which is in solution...]

 

CLASS LESSON

  1. Review worksheet 7.3 to identify vocabulary terms [teach kids to see "assignments" as preparation for assessment and point them to identifying what they need to know and what they will be tested on.
  2. Content fromsection 7.3 of chapter 7 in online biology textbook: p 182-189.
  3. Teach "diffusion"
    • DEMO - Fill a 1 L flask with water and place one drop of dark color into the flask (in front of class).  Kids can observe that the particles are moving.  Discuss possible reasons that particles move (hitting each other) and discuss why they spread out and don't congregate.  [this is open ended question with complex answer - just the discussion is valuable.  However, try to discourage "anthropomorphic" answers like "the red particle love the wide open spaces..." in terms of understanding]
    • DISCUSS - Point out that partilcles of dye move independently of the particles of water; the flask is FULL of water, but the particles of dye still diffuse relative to each other and not relative to the water concentration... [this is NOT easy to understand of explain...and is not necessary at this level]
    • DEMO - have students get onto a table (if strong enough) or cram into a corner and they will "diffuse" away - a visual model.
    • DISCUSS - "farting" and who smells the fart first is something that gets kids attention too :)
  4. Teach "concentration:" (a) emphasize that a concentration is relative to a total volume; (b) increasing the portion of  solvent in volume requires decreasing the volume of solute [see below].  NOTE - concentration is not about absolute number of particles but about the amount of particle per volume of solution.
  5. Fill a 1 L flask with colored water (or previous one!) and then drop marbles or dense, uniform particles into the flask.  Quickly the fluid overflows.  Emphasize that there is limited volume in the container.  In concentrations, when the amount of solvent increases, then the amount of solute decreases - and vice versa.
  6. Draw 3 LARGE shapes on board representing beakers.  In each one draw a single cell and a molecule (like oxygen) that diffuses across cell membranes easily.

    1. Begin with one cell drawn inside of one beaker; draw one oxygen in the cell and one oxygen in the beaker.
      1. Lead students to understand that the "number of oxygen molecules in the cell and in the beaker are the same" in other words the total amount of particles is the same IN  EACH  PLACE.
      2. Next lead students to see (imagine) how much volume the water in the beaker contains or takes up and how much volume is in the cell. 
        • Which volume is greater?
        • Which place has more concentration of oxygen (text defines concentration as mass / volume.
        • Students should understand difference between number of particles and concentration THIS  IS  A  CRITICAL  UNDERSTANDING AND  WILL  BE  ASSESSED!
    2. Demonstrate the inverse effect of concentrations: a solution with MORE solvent must have LESS solute - in a given volume.

  7. Explain terms:  hypertonic, hypotonic & isotonic (use diagrams of beakers to show difference.)

    1. See wikipedia article on tonicity

    2. See wikipedia article on osmosis

 

  • LEAVE SOLUTION AFFECT ON CELLS TILL NEXT CLASS!!

 

 

 

 

ASSIGNMENT

NONE

 

 

Complete assigned work which is in green, above.  Please pay special attention to text in orange.

 

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