Cell Boundaries

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Cell Boundaries

• The gateway between the cell and its
  surroundings.

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Cell Membrane

• Regulates what enters and leaves the cell.
• Provides the cell with support
• Structure Lipid Bi Layer Bi means two so it
  literally means 2 layers of lipids.
• Proteins are also embedded (set in) in the bi
  layer.

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Cell Membrane
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Proteins in the Bi-layer

• There are proteins put into the bi-layer to act
  like doorways or channels for larger molecules to
  move through.
• Lets think of it this way If you wanted to put
  a piano into your living room and it did not fit
  through the door you might have to take out a
  window to get it into the room.
• The cell membrane would be the wall to your house
• The protein would be the channel that allows the
  piano to move in or out of the house or cell.

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Phospholipid Bilayer
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Cell Walls

• Cell walls lie just outside of the cell membrane.
  
• Structure They have holes or pores in them
  that allow water, oxygen, and CO2 to pass into
  and out of the cell.
• Function Provide support and protection for the
  cell.
• Found in plants, algae, fungus, and bacteria.

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Cell Wall
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Movement Through Cell Boundaries

• There are two main types of movement that occurs
  through cell boundaries
• 1. Diffusion
• 2. Osmosis
• The purpose of both of these processes is to
  reach equilibrium on both the inside and the
  outside of the cell.
• Equilibrium When the concentration is the same
  throughout a solution.
• AB

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Diffusion Up Close

• Diffusion occurs when particles move from an area
  of high concentration to an area of low
  concentration.
• No energy is required for this to occur.
• Example When perfume is sprayed out of a bottle
  it is highly concentrated. It exits the bottle
  and diffuses throughout the room until it reaches
  equilibrium.

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Types of Diffusion

• Facilitated Diffusion This occurs when
  molecules move through the cell membrane with the
  help of protein channels.
• There must also be a higher to lower
  concentration gradient.
• No energy is required.
• Passive Transport Filtration and Facilitated
  Diffusion

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Active Transport

• Active Transport occurs when molecules move
  through the cell membrane against a concentration
  gradient.
• This is carried out by protein pumps also located
  in the cell membrane.
• This does require energy.
• Transport Processes Requiring ATP

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Osmosis

• Osmosis occurs when particles in a liquid move
  through a selectively permeable membrane.
• This occurs until equilibrium is reached.
• Example We have a beaker with sugar water in
  it. We put a semi-permeable barrier that cut the
  beaker in half. On one side we added 5 more
  tablespoons of sugar. The water would move from
  the area of lower sugar concentration into the
  area of higher sugar concentration to try to
  dilute the sugar concentration until it was equal
  on both sides.
• The Cell Passive Transport Osmosis

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How Does Osmosis Work?

• Hypertonic When a solution has more solute then
  solvent
• The side of the beaker with the 5 extra
  tablespoons of sugar
• Hypotonic When a solution has less solute then
  solvent.
• The side of the beaker with only the original
  sugar water.
• Isotonic When two solute concentrations are the
  same.
• When both sides have reached equilibrium.