Passive%20Transport%20Notes

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Passive Transport Notes
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Focus Questions

• What is the purpose of passive transport
  biologically?
• Explain how each type of passive transport works.
• Explain what happens when a cell is
  hypertonic/hypotonic to its surroundings.
• How does the structure of the cell membrane
  influence its function and what crosses it?

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Cell Membrane
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Cell Membrane
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Vocabulary to know.

• Permeable Allows things to enter and leave. A
  membrane is permeable to a substance if it lets
  that substance move across it.
• Semi-permeable or selectively permeable
  membranes that allow some substances to move
  across but not others. Most membranes are
  semi-permeable.
• Equilibrium when there are equal amount of a
  substance on both sides of a membrane.

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More Vocabulary

• Solution a mixture of two or more substances
• Example a salt solution salt is dissolved in
  water
• Solute the substance dissolved in a solution
• Example the salt (solute) dissolved in water

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Passive Transport

• When molecules move across the cell membrane from
  an area of high concentration to an area of low
  concentration.
• Does NOT require energy from the cell.
• There are 3 examples..

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1. Diffusion

• Molecules move from an area of high concentration
  to low concentration until equilibrium is reached
  and the molecules are evenly dispersed.

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2. Osmosis

• The diffusion of water across a semi-permeable
  membrane.

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3. Facilitated diffusion

• When large molecules that are too big are helped
  across the cell membrane by carrier proteins
  embedded in the membrane.
• Carrier proteins act as channels that allow large
  molecules to pass.
• Molecules are moving DOWN the concentration
  gradient.
• Concentration gradient the DIFFERENCE in
  concentrations between a barrier (membrane)

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Facilitated Diffusion
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More vocabulary.

• Hypertonic when a cell has a higher
  concentration of a substance than the liquid
  around it, the cell is hypertonic in comparision
  to the liquid
• Hypotonic when a cell has a lower concentration
  of a substance than the liquid around it
• Isotonic when a cell and the solution that is
  surrounding it have an equal concentration of a
  substance.