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HOMEOSTASIS AND TRANSPORT              

•   I. Cell Membranes
• Cell membranes help organisms maintain
  homeostasis by controlling what substances may
  enter or leave cells
• B. Some substances can cross the cell membrane
  without any input of energy by the cell
• C. The movement of such substances across the
  membrane is known as passive transport
• D. To stay alive, a cell must exchange materials
  such as food, water, wastes with its
  environment
• E. These materials must cross the cell or plasma
  membrane
•                                                 
                                                  

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• F. Small molecules like water, oxygen, carbon
  dioxide can move in and out freely
• G. Large molecules like proteins carbohydrates
  cannot move easily across the plasma membrane
• H. The Cell Membrane is semipermeable or
  selectively permeable only allowing certain
  molecules to pass through

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• II. Diffusion
• A. Diffusion is the movement of molecules from
  an area of higher concentration to an area of
  lower concentration
• http//www.biosci.ohiou.edu/introbioslab/Bios170/d
  iffusion/Diffusion.html

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• B. Small molecules can pass through the cell
  membrane by a process called diffusion
• C. Diffusion across a membrane is a type of
  passive transport because it does not require
  energy

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• D. This difference in the concentration of
  molecules across a membrane is called a
  concentration gradient
• E. Kinetic energy keeps molecules in constant
  motion causing the molecules to move randomly
  away from each other in a liquid or a gas

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• The rate of diffusion depends on temperature,
  size of the molecules, type of molecules
  diffusing
• H. Molecules diffuse faster at higher
  temperatures than at lower temperatures
• I. Smaller molecules diffuse faster than larger
  molecules

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• K. Solutions have two parts --- the solute which
  is being dissolved in the solvent
• L. Water serves as the main solvent in living
  things

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• M. Diffusion always occurs down a concentration
  gradient (water moves from an area where it is
  more concentrated to an area where it is less
  concentrated)
• http//www.tvdsb.on.ca/westmin/science/sbi3a1/Cell
  s/Osmosis.htm

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• N. Diffusion continues until the concentration of
  the molecules is the same on both sides of a
  membrane
• O. When a concentration gradient no longer
  exists, equilibrium has been reached but
  molecules will continue to move equally back
  forth across a membrane
• http//www.tvdsb.on.ca/westmin/science/sbi3a1/Cell
  s/Osmosis.htm

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Osmosis

• Think back to solutions solutes and solvents
• Osmosis is the process by which water molecules
  diffuse across a cell membrane from an area of
  lower solute concentration to an area of higher
  solute concentration.
• Direction of movement depends on relative
  concentrations of solutions.

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Direction of movement into cells

• Hypotonic to the cytosol
• solution outside the cell is less concentrated
  than inside the cell
• water moves into the cell
• Hypertonic to the cytosol
• solution outside the cell is more concentrated
  than inside the cell
• water moves out of the cell
• Isotonic
• concentrations are equal
• http//www.tvdsb.on.ca/westmin/science/sbi3a1/Cell
  s/Osmosis.htm

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Red blood cells are placed into 3 different types
of solutions figure out the types of solution in
the beakers by looking at the RBC
HYPOTONIC
ISOTONIC
HYPERTONIC
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How do freshwater organisms deal with osmosis?

• What would be the problem?
• Water would diffuse into the cells
• What would organisms do to deal with the problem?
• Pump water out or excrete large amounts of water

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How do marine organisms deal with osmosis?

• What would be the problem?
• Water would diffuse out of the cells
• What would organisms do to deal with the problem?
• Pump water out or excrete large amounts of salt

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Finish the statements

• Diffusion is
• Osmosis is
• A hypertonic solution has
• A hypotonic solution has
• A cell placed in a hypertonic solution will
• A cell placed in a hypotonic solution will
• Both osmosis and diffusion are _______ transport
  because they do not require _______.

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Active Transport

• Transport Notes
• Active Transport Movie 1
• Active Transport Movie 2