How does stuff get in and out of cells?

1
How does stuff get in and out of cells?

• Active and passive transport across the
• Plasma Membrane (PM)
• Diffusion and Osmosis

2
2 categories of transport across PM

• passive transport no cell energy required.
  Moves along a concentration gradient from areas
  of high concentration to areas of lower
  concentration.
• diffusion
• osmosis
• active transport requires cell energy because
  molecules are transported against a concentration
  gradient

3
Passive Transport

1. Diffusion net movement of particles from an area
   of high concentration (overcrowding) to an area
   of lesser concentration.
2. Osmosis the diffusion of H2O molecules through
   the PM.

4
Diffusion (in detail)

• All objects in motion have kinetic energy move
  in straight line until they collide w/ something
  else.
• 1827 Robert Brown (Scotland)
• Studied pollen under microscope
• Observed random movements of grains
• Called it Brownian motion

• What happens when you put a drop of food coloring
  in water?

5
Diffusion (cont.)

• The goal is to get as far away from other
  molecules as possible?
• From area of high concentration to area of low
  concentration.
• Eventually the particles will be as far apart
  from each other as possible

Fig 2
6

• Key terms
• Concentration gradient diffusion cannot occur
  unless theres an area of high concentration
  (overcrowding).
• Selective permeability The phospholipid bilayer
  of the PM is selective about what passes through
  by diffusion.

7
OSMOSIS
WHAT Diffusion of H2O molecules from higher
concentration to lower concentration. PM lets
water pass through.
concentration of H2O is higher OUTSIDE the cell
than inside the cell so H2O molecules move IN
increases pressure in the cell and cell may
burst
concentration of H2Ois THE SAME inside outside
the cell so there is No Gain or Loss of H2O
molecules Turgor pressure stays the same cell
maintains homeostasis
concentration of H2O is higher INSIDE the cell
than outside so H2O molecules move OUT Turgor
pressure decreases and cell may shrivel up
8
Passive Transport (in detail)

• Substances can pass through PM because it is
  permeable.
• They move WITH a concentration gradient
• They do this via diffusion, osmosis, etc
• Facilitated Diffusion
  Carrier (Transport) Proteins

Membrane protein