Diffusion

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Diffusion

• Chapter 5-4

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Standard 1a

• 1a Students know cells are enclosed within
  semipermeable membranes that regulate their
  interactions with their surroundings

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How is a screen door like a cell membrane?

• How do you think a window screen is similar to a
  cell membrane?
• What are some things that can pass through a
  window screen and some things that cannot? Why
  is it important to keep these things from moving
  through the screen?
• The cell is surrounded by a cell membrane, which
  regulates what enters and leaves the cell. Why is
  it important to regulate what moves into and out
  of a cell?

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Movement Through the Membrane

1. Cell Membrane
2. Diffusion
3. Osmosis
4. Facilitated Diffusion
5. Active Transport

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Structure of the Cell Membrane
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Diffusion

• Diffusion process by which molecules of a
  substance move from areas of higher concentration
  of that substance to areas of lower concentration
• Demonstration Cologne

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Passive Transport
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Osmosis

• Some compounds cannot move through a cell, but
  water CAN.
• Instead of the substance moving, water moves
  instead.
• Osmosis diffusion of water molecules through a
  selectively permeable membrane.

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Osmosis
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Facilitated Diffusion

• Back to my screen door
• If my dog needs to move in and out of the house,
  what does he need?
• Facilitated diffusion Molecules are transported
  across a membrane by a carrier protein

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Facilitated Diffusion
Glucose molecules
High Concentration
Cell Membrane
Low Concentration
Protein channel
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Active Transport

• Sometimes, cells need to move molecules AGAINST a
  concentration gradient
• (low ? high)
• Active transport energy-requiring process that
  enables material to move across a cell membrane
  across a concentration difference.
• REQUIRES ENERGY!

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Active Transport
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Large Transport

• When cells want to take in large molecules or
  large quantities of liquids, they will envelope
  the solid or liquid by the cell membrane and then
  swallow it into the cell.
• Phagocytosis Taking in solids by folding in of
  cytoplasm
• Pinocytosis Taking in liquids by folding in of
  cytoplasm

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Large Transport

• Exocytosis Taking out large solids or liquids by
  a vescicle merging with the cell membrane.

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