Cellular Processes

1
Cellular Processes

• Diffusion- movement of molecules form a region of
  high concentration to a region of low
  concentration
• Equilibrium The number of molecules moving in
  one direction is equal to the number in the other
  direction system balanced

2
Cellular Processes

• Selectively Permeable Membrane
• allows some substances to cross the membrane
  more easily than others and blocks the passages
  of some substances altogether
• Example Window screen lets air in blocks
  mosquitoes
• http//www.phschool.com/science/biology_place/bioc
  oach/biomembrane1/permeability.html

3
Passive Transport

• Diffusion across a membrane requiring only the
  random motion of molecules with no energy
  expended by the cell
• Example) Water, Oxygen, Carbon dioxide
• http//www.phschool.com/science/biology_place/bioc
  oach/biomembrane1/transport.html

4
Facilitated Diffusion

• Transport proteins provide a pathway for certain
  molecules to pass
• The word facilitate means to help
• Examples Some ions and small polar molecules
  such as water and sugar diffuse into and out of
  the cell

5
Osmosis

• the passive transport of water across a
  selectively permeable membrane
• http//www.phschool.com/science/biology_place/bioc
  oach/biomembrane1/osmosis.html
• http//www.tvdsb.on.ca/westmin/science/sbi3a1/Cell
  s/Osmosis.htm

6
Water Balance in Animal Cells

• In a hypotonic solution an animal cell gains
  water, swells, and may even pop like an
  overfilled balloon
• In a hypertonic environment the animal cell loses
  water, shrivels, and may die
• Animals living in an aquatic environment depend
  on mechanisms within their bodies to help prevent
  a build up of water in the body

7
Water Balance in a plant cell

• A plant cell is firm and healthiest in a
  hypotonic environment
• Example Bathed by rainwater- the cell becomes
  firm as a result of the net flow of water inward,
  pressure applied prevents the cell from taking in
  too much water and bursting
• Plant cells in an isotonic environment become
  limp
• Plant cells in a hypertonic environment are no
  better off than an animal cell

8
Active Transport

• When a cell expends energy to move molecules or
  ions across a membrane
• A specific transport protein pumps a solute
  across the membrane in a direction from lesser
  concentration to greater concentration
• Example potassium ions (K) and sodium ions (Na)

9
Transport of Large Molecules

• Vesicles small membrane sacs that specialize in
  moving products into, out of, and with in a cell
• Exocytosis process of exporting proteins from
  the cell by a vesicle fusing with the plasma
  membrane
• Endocytosis process of taking material into a
  cell within vesicles that bud inward from the
  plasma membrane
• http//www.phschool.com/science/biology_place/bioc
  oach/biomembrane2/cytosis.html
• http//www.bbc.co.uk/education/asguru/biology/01ce
  llbiology/05pathways/09endoexo/index.shtml