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Diffusion and Osmosis. Bio 21L Spring 2003. Molecular Motion. Molecules posses kinetic energy. Random motion Rotational, translation & vibration movements Brownian Movement: random, zigzag movement, arising due to collisions of molecules with particles. BM is typical of colloids.

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diffusion and osmosis

Diffusion and Osmosis

Bio 21L

Spring 2003

molecular motion
Molecular Motion
  • Molecules posses kinetic energy.
  • Random motion
  • Rotational, translation & vibration movements
  • Brownian Movement: random, zigzag movement, arising due to collisions of molecules with particles.
  • BM is typical of colloids.
diffusion
Diffusion
  • Net movement of molecules from an area of high concentration to one of lower concentration
  • Fick’s First law of Diffusion:

Rate of diffusion is directly proportional to concentration

osmosis
Osmosis
  • Diffusion of molecules across a semi-permeable membrane from a place of higher concentration to one of lower concentration until the concentration on both sides is equal
  • Osmolarity: Concentration of osmotically active particles
  • Tonicity: The osmotic pressure/tension of a solution wrt blood
  • Hypertonic solutions: are @higher osmotic pressure than the reference solution
slide5
Hypertonic solutions: are @ higher osmotic pressure than the reference solution. Exosmosis
  • Hypotonic: are @ lower pressure than reference. Endosmosis
  • Isotonic: are @ the same osmotic pressure as reference; e.g. 0.9% NaCl Sol; 5% sucrose sol with human blood cells
dialysis
Dialysis
  • Separation of molecules based on size, using a semi-permeable membrane.
  • Semi-permeable membranes: natural-cell membranes; synthetic- nitrocellulose memb.
  • Factors affecting rate: Pore size of memb; Size of molecule; polarity of molecules; tonicity of solution outside dialysis bag
water potential uptake of water by plants
Water Potential ۴ & Uptake of Water by Plants
  • Forces of adhesion & cohesion
  • Evaporation & transpiration at leaf tip
  • Generation of water potential
  • Endosmosis into root cells
  • Water uptake
haemeolysis crenation ghost studies
Haemeolysis & Crenation: Ghost Studies
  • Loss of water by cells- cell shrinkage or crenation
  • In RBCs-leaves just membranes-used extensively to study memb structure
  • In plant cells- cell shrinkage- allows plant cell memb to be seen
  • Plasmolysis-rupturing plant cells by dunking in hypotonic solution.
  • Turgid cell- plant cells that maintain a good osmolarity & tonicity- appear round & happy!