Chapter 4 by yurtgc548

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									Chapter 4


  On the Move
Diffusion
Note:
 Particles (molecules) in liquids and gases
  about, at high speeds, in all directions.
 Particles (molecules) will escape from the
  concentrated area to places where there are
  fewer or no particles.
Diffusion in Liquids
A drop of potassium permaganate is placed
in a test tube of water. Observe what
happens.


Question:
What happens to the water after a few
minutes?
Where do you think the drop originates from?
   The
top or bottom of the liquid?
Diffusion in Liquids
Diffusion in Gases
A tube of bromine gas is connected via a
valve to another empty container.


Question:
What is the colour of bromine gas?
What happens in the left hand tube?
What happens in the valve?
What happens in the right hand container after a
while?
What can you say about the pathway of the bromine gas?
Diffusion in Gases
Diffusion
The movement of molecules from a
   region
of higher concentration to a region
   of
lower concentration is called
   diffusion.
Diffusion takes place in liquids and
   gases.
Osmosis
 Osmosis is a special form of diffusion.
 The MOVEMENT OF WATER from a
  dilute solution to a more concentrated
  one through a PARTIALLY PERMEABLE
  MEMBRANE.
 This type of membrane, (also called
  semi-permeable) allows only water
  but not other (dissolved) substances
  to pass through.
Osmosis




 Water concentration is lower in the beaker
  than in the bag.
 This causes water to move from the bag
  (left) into the beaker (right).
Osmosis in an Animal Cell
 All cells (plants and animal) are
  surrounded by a partially permeable
  membrane and the cytoplasm
  contains dissolved substances eg.
  Salt and proteins.
 Whether or not water enters the cell
  depends on the relative concentration
  of the cytoplasm and the fluid
  surrounding it.
An Animal Cell in Distilled
Water
 What happens when there are more water
  molecules in the surrounding fluid than the
  cell?
 What do you think happens to the cell if it
  is placed in concentrated salt solution?
A Plant Cell in Distilled Water
Osmosis in Plants
 Plants gain water by osmosis through
  their roots, and it is osmosis that
  moves water into plant cells, making
  them turgid or stiff, and thus able to
  hold the plant upright.
Test Byte 1
 What happens if the water
  concentration is the same on both
  sides of the membrane?
Diffusion vs Osmosis
        Diffusion              Osmosis

  Random movement        Random movement
                         of water
  From higher to         From higher to
  lower concentration    lower concentration

Remember:
 Molecules move in all directions in diffusion
  and osmosis.
 Osmosis is the diffusion of water.
Test Byte 2
In what direction will the water flow in the
following situations?
What happens to the cell (if any)?
Situation 1:
Situation 2:
Situation 3:
Test Byte 3
 In each of the following pictures, describe
  the relative concentration of water in the
  cell and the surrounding fluid.

								
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