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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 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.
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 • 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
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 • 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 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 • 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!
