Chapter 5: Homeostasis

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Chapter 5 Homeostasis Transport

• Section 1
• Passive Transport

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Passive Transport

• Movement of substances across the cell membrane
  without energy input from the cell itself.

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Types of Passive Transport

• Diffusion
• Osmosis
• Facilitated Diffusion
• Diffusion through ion channels

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Diffusion

• Movement of molecules from an area of higher
  concentration to an area of lower concentration.
• Simplest type of passive transport.
• Concentration gradient is the difference in the
  the concentration of molecules across a space

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Diffusion (continued)

• Driven entirely by kinetic energy of the
  molecules.
• Kinetic Energy Energy of motion
• Molecules are always in constant motion
• Tend to move down concentration gradient.

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Equilibrium

• Diffusion eventually causes EQUILIBRIUM
• State when the concentration of molecules of a
  substance is the SAME throughout a space.

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Diffusion Through A Membrane

• If a molecule can pass through a cell membrane,
  it will diffuse from an area of high
  concentration on one side of the membrane to a
  lower concentration on the other side of the
  membrane.

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What can diffuse through a membrane?

• Size
• Must be small enough to pass through protein
  pores in the cell membrane
• Chemical Nature
• Must be able to dissolve in lipids (non-polar
  molecules)

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Osmosis

• Process by which water molecules diffuse across a
  cell membrane from an area of higher
  concentration to an area of lower concentration.

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HYPOTONIC

• When there is a lower concentration of solute
  outside the cell, the solution outside the cell
  is HYPOTONIC
• Water moves into the cell

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ISOTONIC

• When concentration of solutes outside and inside
  the cell are equal
• Water moves equally in and out of cell

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HYPERTONIC

• When there is a higher concentration of solute
  INSIDE the cell, the solution is HYPERTONIC
• Water moves out of the cell

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Effects of Osmosis

• Animal cells
• Cytolysis take in water (burst)
• Crenation lose water (shrink)
• Plant cells
• Turgor pressure take in water
• Plasmolysis lose water (wilt)

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Effects of Osmosis
Some unicellular organisms living in freshwater
use contractile vacuoles to pump excess water out.
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Facilitated Diffusion

• For molecules that cannot rapidly diffuse across
  a membrane
• Either they dont dissolve in lipids or they are
  too large to go through the membrane
• Molecules are assisted across the membrane by
  carrier proteins

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Facilitated Diffusion
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Ion Channels

• Involves membrane proteins designed to help
  specific ions pass through the membrane

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