Membranes and Passive Transport

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Membranes and Passive Transport

• Ch. 6.2-6.3

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Review

• Cell membranes are made up of some type of lipid
• What is unique about the interaction of lipids
  and water?
• Lipids are hydrophobic, or water resistant, to
  water!
• Why do molecules like these work well for a
  cells boundary?
• Cell cytoplasm is mostly water and cell exterior
  is mostly water --gt water resistant molecule
  makes a good boundary layer

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Objectives

• Structure of cell membranes
• Function of proteins in cell membranes
• Relate diffusion to equilibrium
• Describe passive transport
• Relate osmosis to solute concentration

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Phospholipid Molecule

• Structured like a fat molecule, but only 2 tails
• Hydrophilic Head
• Hydrophobic Tail

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Phospholipid Bilayer

• Phospholipid Bilayer
• Selectively permeable membrane
• surrounds cell
• Controls what goes in and out!
• Online Activity 6.3
• Contains proteins
• What do these proteins do?

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Function of Proteins in bilayer

• Cell communication
• Assist with passage of materials
• Classroom analogy
• Light, heat, electricity, internet, etc.

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Regulating Traffic

• Materials such as water, nutrients, dissolved
  gasses, ions and wastes must CONSTANTLY move in
  two-way traffic across membrane
• Cell membranes function like gatekeepers
• Some molecules pass, others do not!
• How do they do this?

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Ways to get materials across membrane

• Diffusion
• Movement of particles from HIGHER--gt LOWER
  concentration
• The goal is to achieve an equilibrium
• Equilibrium
• in balance
• Perfume?

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Ways to get materials across membrane

• Passive Transport
• Diffusion across a membrane
• no energy
• Some molecules too big to get through membrane
  alone (sugars). Need help!
• What can help them?

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Ways to get materials across membrane

• Facilitated Diffusion
• use of transport proteins
• No energy
• Facilitated Diffusion animation

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Are all substances able to pass through membrane?

• No!
• Diffusion occurs through a selectively permeable
  membrane
• Selectively permeable membrane
• Allows select substances through
• Similar to a window screen air but no mosquitoes

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Water can pass, but sucrose too big
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Three Ways to Get Materials Across Membrane
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How does water get through?

• Osmosis
• Diffusion of H2O
• Hypertonic Solution
• Net water flow OUT of cell
• Hypotonic Solution
• Net water flow INTO cell
• Isotonic Solution
• Equal water flow
• Osmosis Animation
• Sore throat, thirsty after salty snacks

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