1. 4rth
Summary- Experiments with Membranes, Osmosis& Selective Transport Dr.
Matt Holden March 29, 2014
Osmosis is the spontaneous net movement of solvent molecules through a partially
permeable membrane into a region of higher solute concentration, in the direction
that tends to equalize the solute concentrations on the two sides. It is also a physical
process in which any solvent moves across a semipermeable membrane separating
two solutions of different concentrations. Cell membranes are impermeable to large
and polar molecules, such as ions, proteins, and polysaccharides. They are
permeable to non-polar and/or hydrophobic molecules like lipids as well as to small
molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Cell membranes
consist of the phospholipid bilayer with embedded proteins. In this lab we observed
the relationship between lipid membrane and osmosis or transport. In order to
observe this, we put two aqueous droplets of lipid solution in oil, and after a few
minutes we saw the pairs of droplets rolling together and forming a lipid bilayer. We
did this to observe how the membrane influences transport of water and other
substances. When the membrane fused some of the droplets broke while others
formed a bilayer and osmosis occurred. The second part of the experiment consisted
of creating more lipid bilayers between A vesicles and resorufin dyed vesicles, which
must be amphipathic so that the dye can pass from one molecule to another. After
the DIBs are formed, a diffuser is placed on top of the chip containing the DIBs to
diffract the light for better quality of the image. Then, the DIBs are illuminated using a
laser pointer, which excites the electrons in the dye when absorbing a photon. The
excess energy is given off as heat or fluorescence light, and since the fluorescence
concentration was high, residence energy transfer between molecules occurred. As a
result, the membranes were selectively permeable because polimers in the
membrane did not let the dye molecules pass. In this lab, transport rates of water
and other molecules depending on the composition of membranes were observed as
osmolytes and dyes were inserted into droplets of DIBs. This experiment can be
applied to cure diseases related to lipids by changing its composition so it can either
absorb more water or inhibit its water absorption. This experiment helps scientist to
understand the influence the cell membrane has on transporting substances.