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The Plasma Membrane and Transport across it

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The Plasma Membrane and Transport across it Cell Membrane Controls what enters and leaves the cell Like water, nutrients and waste The membrane is Selectively ... – PowerPoint PPT presentation

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Title: The Plasma Membrane and Transport across it


1
The Plasma Membrane and Transport across it
2
Cell Membrane
  • Controls what enters and leaves the cell
  • Like water, nutrients and waste
  • The membrane is Selectively Permeable
  • Membrane selects which molecules can permeate
    (pass through) into the cell.
  • Like a window screen allows what you want in
    and keeps others out.

3
Structure of Plasma Membrane
  • Lipid Bilayer (2 layers of phospholipids)
  • Lipids with phosphate heads attached
  • Head of phospholipid is polar
  • Hydrophilic (points outward, likes watery
    environment)
  • Fatty acids (tails) are nonpolar
  • Hydrophobic (points inward, avoids water)

4
Other Membrane Molecules
  • Membrane Proteins - (transport)
  • Allow substances/waste to move in and out of the
    cell.
  • Creates a tunnel that can be closed or open.
  • Carbohydrates/ Other Proteins-
  • Stick out of cell surface (id card for other
    cells to see)

5
Cell Membrane Structures
6
How stuff gets into the cell
  • 2 ways cell gets nutrients it needs and gets rid
    of waste
  • Passive Transport
  • Requires no energy
  • Active Transport
  • Requires an input of energy

7
PassiveTransport
  • Occurs due to concentration gradient
  • Molecules naturally move from areas of higher
    concentration to lower concentration (no energy
    required)
  • Diffusion natural movement of molecules
  • Facilitated Diffusion through protein channels
  • Osmosis diffusion of water molecules

8
Diffusion
  • In nature, molecules ALWAYS move from areas of
    higher concentration to areas of lower
    concentration, as is shown in this picture.
  • They move to reach equilibrium
  • This also happens across the cell membrane!

These odor molecules are diffusing from the
bottle (area of high concentration) to the
surrounding air (lower concentration)
9
Facilitated Diffusion
  • Diffusion of molecules through protein channels
    in the cell membrane
  • Used for substances that the cell needs but
    cannot pass through the membrane
  • Large molecules
  • Charged (ions)

10
Osmosis
  • The diffusion of water molecules is called
    osmosis
  • Just like diffusion
  • Water molecules move from areas of higher conc.
    to areas of lower water conc.
  • They will move until there are equal
    concentrations of water (and solute) molecules
    everywhere
  • Called equilibrium
  • Molecules still diffuse, but at equal rates

11
Osmosis
  • The movement of water molecules across a membrane
  • Water moves from areas of high water conc. to
    areas of lower water conc.
  • This is how cells maintain a stable internal
    environment
  • Homeostasis reacting to environment

Blue water molecules, easily pass through
membrane Red large (or charged) molecules,
cant pass through membrane
12
Passive Transport Video
13
Isotonic Solutions - Iso equal
  • Cells that are in equilibrium with the
    surrounding solution do not experience osmosis.
  • These cells have the same concentration of solute
    (and water) as the surrounding solution

14
Hypotonic Solutions hypo lower
  • solute (solute concentration) is lower outside
    the cell
  • More water outside, so water moves into the cell,
    to try to reach equilibrium
  • The cell swells with the extra water.
  • Animal cells may swell so much, they may burst
    (especially in pure water)
  • Plant cells cell swells and membrane pushes
    against the cell wall
  • Like celery in water crisp/ rigid from pressure
    on cell walls

15
Hypertonic Solutions - hyper higher
  • solute is higher outside of the cell.
  • Less water outside the cell, more inside. Water
    moves out of the cell.
  • Animal cells shrivel because of water loss.
  • Plant cell membranes move away from cell wall as
    water moves out.
  • Why plants wilt.

16
Other Forms of Transport
  • Active Transport (needs energy)
  • Large particle transport
  • Endocytosis cell surrounds molecule(s), which
    are then engulfed by cell
  • doesnt pass through membrane
  • Exocytosis - expulsion/secretion of materials.
    Opposite of endocytosis

17
Active Transport (cont)
  • Movement of molecules against (up) the
    concentration gradient
  • From areas of lower concentration to areas of
    higher concentration
  • For instance, if a cell needs a high
    concentration of something (that would normally
    diffuse OUT of cell)

18
Summary!
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