The Plasma Membrane

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The Plasma Membrane
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Plasma Membrane

• The outer layer of a cell is semi-permeable.
• Semi-permeable means that only certain molecules
  can pass through it.

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Plasma Membrane

• Has two layers of lipid molecules -Phospholipid
  bilayer
• Polar heads point to the outside (Phosphate head)
• Non-polar (straight) tails form the inside of the
  membrane

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Fluid Mosaic Membrane

• Its called a fluid mosaic membrane because it is
  a mosaic of different kinds of molecules. These
  include
• lipids
• protein
• carbohydrate chains

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The 3 Ways a Cell regulates what comes into a
cell

• Simple Diffusion some materials move into and
  out of the cell without using energy.
• Carrier Facilitated Diffusion movement into the
  cell through a protein in the plasma membrane
• Active Transport use energy in the form of ATP
  to move other molecules into and out of the cell

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Comparison of Active Transport and Passive
Transport (continued)

• Most solutes can cross the membrane only if there
  is a carrier protein or a channel protein to
  transfer them.
• Passive transport, in the same direction as a
  concentration gradient, occurs spontaneously,
  whereas transport against a concentration
  gradient (active transport) requires an input of
  energy. Only carrier proteins can carry out
  active transport, but both carrier proteins and
  channel proteins can carry out passive transport

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Diffusion

• In a solution, molecules move constantly.
• They collide with each other and tend to spread
  out randomly.
• The molecules tend to move from an area where
  they are more concentrated to an area where they
  are less concentrated, a process known as
  diffusion.

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Diffusion

• Diffusion "goes from the higher concentration
  side to the lower concentration side".
• There is no energy input to cause diffusion
• It simply occurs due to the random motion of the
  substance moving across the plasma membrane.

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Diffusion

• Even after the solution has reached equilibrium,
  individual molecules continue to move rapidly
  across the membrane in both directions.

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Osmosis

• Diffusion of water through a semi-permeable
  membrane.
• Not all substances can cross cell membranes.
• If something can cross the cell membrane then the
  membrane is permeable.
• The cell membrane is described as being
  selectively permeable.
• Cell membranes are selectively permeable, which
  means that some substances can pass across them
  and others cannot.

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Osmosis

• Osmosis the diffusion of water through a
  selectively permeable membrane.

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Carrier Facilitated Diffusion

• Facilitated Diffusion movement of specific
  molecules across cell membranes through protein
  channels

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Active Transport

• Active Transport - when material moves from an
  area of lower concentration to an area of greater
  concentration
• Active transport requires the cell to spend
  energy, usually in the form of ATP.

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Review Questions

• The ____ of a phospholipids is polar, and the
  long _______ are non-polar.
• What does the term selectively permeable mean
  in regards to a cell membrane.
• What are the three major ways of taking in or of
  regulating the passage of materials into and out
  of the cell?
• True or False, Osmosis of water is a form of
  diffusion.

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Warm-Up Label the diagram with as much detail
as possible.

• Phospholipid
• Phosphate Head
• Hydrophilic
• Fatty Acid Tails
• Hydrophobic