Teacher Preparation

1
Teacher Preparation

• Slice a potato so the slices are approximately
  the same thickness
• Place ½ the slices in a beaker of salt water
  the other ½ in a beaker of distilled water. (Do
  30 minutes ahead of class start so water movement
  happens) Around mid-morning prepare a second set
  of beakers for the afternoon classes. (Use
  plastic beakers or bowls)
• Run off boot camp arrows and diffusion cards
• Run off osmosis worksheet

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Biology 4B

• Investigate and Identify cellular processes
  including homeostasis, permeability, energy
  production, transportation of molecules, disposal
  of wastes, function of cellular parts, and
  synthesis of new molecules.

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What Happened?

• Your teacher will pass around two beakers
  containing cut up vegetables and water. Salt
  water is the liquid in one of the beakers. The
  other beaker contains distilled water. Feel the
  vegetables.
• Are the vegetables firm or soft?
• Compare the feel between the two bowls
• What happened to cause this difference? We will
  discuss it in a few minutes.

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BEAKER

• The Beaker I am showing you contains water
• I will place a drop of food coloring in it.
  Please watch and try to explain what is happening
• We will revisit this later in the period.

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In your biology class, you learned that all
living things are made of cells

• Each of the vegetable slices you felt is composed
  of thousands of cells that are bound together
• Each one of these cells is held together by a
  cell membrane or plasma membrane

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Cell Membrane
The Cell or Plasma Membrane Surrounds and Holds a
Cell Together. It also controls what substances
can enter or leave a cell.
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In or Out?

• How is a window screen similar to a cell or
  plasma membrane? Read on to find out.
• 1.What are some things that can pass through a
  window screen?
• 2.What are some things that cannot pass through a
  window screen? Why is it important to keep these
  things from moving through the screen?
• 3. The cell is surrounded by a cell membrane,
  which regulates what enters and leaves the cell.
  Why is it important to regulate what moves into
  and out of a cell?

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Like a screen the cell/plasma membrane is
semi-permeable or selectively permeable
Water
NaCl Salt
Starch
Lugols Iodine
C6H12O6 Glucose
Inside Cell
Outside Cell
Which substances can go through the pores?
Pores
Answer Water, Lugols, Glucose (Starch, Salt are
too big!)
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SOLUTIONS

• Is a homogenous mixture of a solute in a solvent
• Solute - molecule that is dissolved
• Solvent - what dissolves the molecule
• Concentration-the amount of solute in the
  solvent (3 salt 97 water)

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Water is the Solvent Sugar is the Solute
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Solution Examples ½ Milk .5 fat and 99.5
milk/water 1 Milk 1 fat and 99
milk/water 2 Milk 2 fat and 98 milk/water
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Kinetic Energy

• Energy of Motion
• Molecules are always in motion
• Solids - slow
• Liquids - medium
• Gases-fast

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Diffusion

• Movement of a substance from high concentration
  to low concentration (kinetic energy) ( Ex
  Diffusion of smoke, perfume etc in a room.)

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Equilibrium-Discuss Beaker Demo

• When the rate of particles into or out of an area
  is equal. (The particles do NOT quit moving but
  their net movement is zero)

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Osmosis - movement of water from high
concentration to low concentration
Dialysis Tubing Bag Contains 10 Starch and 90
Water
20 Lugols Iodine 80 Water
If the dialysis tubing bag is placed in the
Lugols Iodine bowl what will happen? (The
tubing has pores)
Answer Lugols Iodine will diffuse in the bag
from high to low concentration, osmosis will
occur and water will come out of the bag from
high to low concentration but starch molecules
are too big to pass through the bag.
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Diffusion of Sugar and Osmosis of Water
Movement from higher concentration to lower
concentration
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Osmosis Diffusion Can Occur at the same time
Which Substance will move and why?
Distilled Water has no minerals so it is 100
water
The distilled water molecules will move by
osmosis into the glucose solution the glucose
will diffuse into the distilled water. In both
cases substances move from high to low
concentration.
This solution is 8 glucose the rest is water
(92)
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Boot Camp Cards Arrows

• Class Participation

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20

• Perfect Situation If a cell with 3 salt
  solution is in an equal solution of 3 salt,
  then equilibrium is reached and concentrations
  are equal.

Water goes in out of cell at the same rate
Notice normal appearance
Water molecules still move but they move equally
in and out of the red blood cells.
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• If a cell with 3 salt solution is placed
  in a 10 salt solution outside the cell then
  water would leave the cell and the cell
  dehydrates and shrinks

Notice shrunken appearance
Water leaves cell
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Problems with Osmosis

• If a cell with a 3 salt solution inside
  the cell (97 water) is placed in distilled water
  (100 water), then it could lyse (or burst)

Water goes in
Notice swollen appearance
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Factors Affecting Particle Movement
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CONCENTRATION

• Concentration-the amount of solute in the solvent

The more concentrated a substance is, the faster
it diffuses.
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PARTICLE SIZE
Particles with more mass move slower than those
with less mass.
In this picture a crystal of iodine (brown) and
crystal of methylene blue (blue) were place on
clear agar for 15 minutes. Which one diffused
more? The iodine has less mass.
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TEMPERATURE
Atoms Molecules movement increases with
increased temperature
In this previous slide it took 15 minutes for the
diffusion to happen. This petri dish was placed
on a hot plate and the iodine and methylene blue
diffused in two minutes. Why?
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WHAT HAPPENED?

• Explain in terms of osmosis why the salt water
  vegetables felt limp?
• Explain, in terms of osmosis, why the distilled
  water vegetables felt very turgid. (Hard)

99 H2O 1 salt
99 H2O 1 salt
80 H2O 20 Salt Salt Water
100 H2O Distilled Water
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Think about it!

• A cucumber is normally 99 water and 1 salt.
  Explain what would happen and WHY, if
• The cucumber were placed in a solution of
  distilled water. (Distilled water is 100 water)
• The cucumber were placed in a solution of 80
  water 10 salt.
• The cucumber were placed in a solution of 99
  water 1 salt.

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Practice Questions

• When a sea urchin egg is removed from the
  ocean and placed in freshwater, the egg swells
  and bursts. Which of these causes the water to
  enter the egg?
• A Coagulation
• B Sodium Pump
• C Active Transport
• D Osmosis

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Practice Questions

• The picture shows a cell model and the
  solutions associated with it. In this situation
  the cell model will-
• A gain mass
• B shrink
• C increase in solute
• D start to vibrate

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Practice Questions

• Which of these best explain why a freshwater
  aquarium would be a dangerous habitat for
  saltwater fish?
• A The tissues of the saltwater fish would
  absorb too much acid
• B The organs of the saltwater fish would
  produce too much protein
• C The organ systems of the saltwater fish
  would consume too much energy
• D The cells of the saltwater fish would gain
  too much water

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Your Turn-Complete the Review Questions