Transporting Materials Across the Cell Membrane

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Transporting Materials Across the Cell Membrane

• Osmosis, Diffusion, and Active Transport

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Demonstration

• Sketch a diagram of the beaker and water
• Get a colored pencil and draw what happens the
  instant the dye hits the water

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Diffusion

• Is the movement of materials from a region of
  high concentration to a region of low
  concentration
• Equilibrium is reached when the concentrations
  are equal
• You experience this when burnt toast from the
  kitchen wafts down to your room

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Demonstration, contd

• Observe the beaker with dye now
• How is it different from when the dye first went
  in?

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Osmosis

• Is the movement of water from a region of high
  concentration to a region of low concentration
  until equilibrium is reached
• You experience osmosis when lettuce left out on
  the counter wilts the water is moving from high
  conc (in lettuce) to low conc (in air)

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• Both diffusion and osmosis are passive do not
  require ATP (energy)

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Cell Membrane

• Is composed of a double layer of lipid molecules
  in which proteins are embedded
• Cell membrane regulates passage of substances
  into and out of the cell and is said to be a
  selectively permeable membrane, meaning not all
  substances will pass through it

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Cell Membrane
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Cell Membrane

• Many substances can pass freely through the cell
  membrane, such as water, CO2 and O2
• Other substances are too large to fit through the
  pores and need help. Carrier proteins aid in
  moving large molecules from the outside to the
  inside of the cell. This is called

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Facilitated Diffusion Demonstration
Note that molecules are moving from a region of
high conc to a region of low conc. Therefore,
this is still diffusion.
http//bio.winona.msus.edu/berg/ANIMTNS/FacDiff.ht
m
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How Facilitated Diffusion Works

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter2/animation__how_facilitated_d
  iffusion_works.html

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Active Transport

• Sometimes substances that need to get into cells
  are in higher conc in the cells diffusion wont
  work
• Some materials are transported against a conc
  gradient (from low to high). In these cases
  energy must be used. Energy in cells is ATP.

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Active Transport

• Active transport is the movement of a substance
  from a region of low conc to a region of high
  conc with the expenditure of energy
• Without active transport, your kidneys would not
  reabsorb precious water, your muscles would not
  contract, and your nerves could not carry
  impulses.

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Active Transport
Carrier proteins require energy in the form of
ATP to move the substances across the membrane
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Endocytosis

• Very large molecules must sometimes get into the
  cell but will not fit through the pores nor the
  carrier proteins
• Endocytosis is a process where a cell engulfs
  large particles by extending its cytoplasm around
  the particle, trapping the particle in a vacuole.

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Endocytosis

• Two types
• Phagocytosis is when the cell engulfs solid
  particles
• Pinocytosis is when the cell engulfs liquid
  droplets.

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Exocytosis

• Exocytosis is the process by which large
  molecules are transported out of the cell, such
  as waste materials.
• The Golgi complex packages the departing
  substances into vesicles, which fuse with the
  cell membrane and rupture, dumping their contents
  to the outside.

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Exocytosis
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Endocytosis/Exocytosis Animation

• http//highered.mcgraw-hill.com/olc/dl/120068/bio0
  2.swf

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Summary
Passive (no ATP required) Active (ATP required)
Diffusion Active Transport
Osmosis Endocytosis
Facilitated Diffusion Exocytosis