Homeostasis

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Homeostasis the
Plasma Membrane
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Structure of the Plasma Membrane

• 2 layers of lipids with proteins embedded within
  each layer
• The lipids are called phospholipids
• They have a polar head and a non-polar tail
• HEAD
• phosphate group which is soluble in water
  (hydrophilic)
• TAIL
• fatty acid chain that is not soluble in water
  (hydrophobic)

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Structure of the Plasma Membrane
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Structure of the Plasma Membrane

• The plasma membrane is referred to as a fluid
  mosaic model
• The plasma membrane is made up of many molecules
  which are free to move sideways
• Fatty acid chains can be saturated or unsaturated
• The more unsaturated fatty acids a membrane has,
  the more fluid it is.
• Saturated or cholesterol chains are more rigid
  and stable

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Structure of the Plasma Membrane
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Maintaining a Balance

• Living cells maintain a balance by controlling
  what goes into and out of the cell
• The plasma membrane is a selectively permeable
  membrane it has the ability to allow some
  materials to pass through and keep others out
• This also allows some cells to carry out
  different jobs than other cells

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Maintaining a Balance

• Some molecules can readily pass across the
  membrane while others cannot.
• The size, polarity, and nature of the molecules
  will determine whether it passes readily or not

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Diffusion

• Diffusion is the net movement of particles from
  high concentration to low concentration
• Diffusion cannot occur unless a substance is in a
  higher concentration in one region than in
  another. This difference is called a
  concentration gradient.
• Dynamic equilibrium there is continuous
  movement, but no overall change
• Dynamic movement
• Equilibrium balance

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Diffusion
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Osmosis

• Osmosis is the diffusion of water molecules
  through a selectively permeable membrane from an
  area of high concentration to an area of low
  concentration
• A cell will lose water if it is placed in an
  environment in which the water concentration is
  lower than that of the cell contents

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ISOTONIC SOLUTION

• The concentration of a dissolved substance is the
  same as the concentration outside the cell.
• Water molecules will still move, but there is no
  net movement of water.
• No osmosis occurs b/c the cell is in dynamic
  equillibrium

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HYPOTONIC SOLUTION

• The concentration of dissolved substances is
  lower than the concentration within the cell
• Water will rush into the cell causing an increase
  in pressure
• This pressure is called turgor pressure

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HYPERTONIC SOLUTION

• The concentration of dissolved substances is
  higher than the concentration inside the cell
• Water will rush out of the cell causing it to
  shrink
• This loss of water from the cell is called
  plasmolysis

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EFFECT of OSMOSIS on RED BLOOD CELLS
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EFFECTS OF OSMOSIS ON CELLS WHEN PLACED IN
DIFFERENT SOLUTIONS
SOLUTION TYPE Concentration of dissolved substances (solutes) Concentration Gradient Results in Animal Cells Results in Plant Cells
ISOTONIC Same as the living cell Zero No change No Change
HYPOTONIC Lower than the living cell Net water movement into the cell Cell swells and bursts Pressure created by excess water stored in central vacuole
HYPERTONIC Higher than the living cell Net water movement out of the cell Cell shrinks plasmolysis Central vacuole collapses and plasmolysis occurs
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Passive transport

• When the cell does no work in moving particles
  across the membrane
• Transport proteins allow needed substances or
  waste materials to move through the plasma
  membrane
• The passive transport of materials across the
  plasma membrane by means of transport proteins is
  called facilitated diffusion.

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Active transport

• The transport of materials against a
  concentration gradient which requires energy.
• BOTH endo- and exocytosis requires energy to move
  materials through the membrane
• Endocytosis
• the cell surrounds and takes in materials from
  its environment
• Exocytosis
• used to expel wastes