Estimating water potentialWhen and by whom was osmosisdiscovered? Osmosis was discovered by a French physiologist Henri Dutrochet in1826.
What is osmosis? Osmosis is the spontaneous transference of watermolecules through a semi-permeable membrane from a weak or dilute solution to astrong concentration, to equalize the amount of H20 on both sidereaching an equilibrium. The time taken to reach an equilibrium depends on thetissue type, temperature and size of the molecules. Water molecules are smallenough to pass through the semi-permeable easily.
However, if a molecule suchas glucose is added to one side of the membrane it cannot pass through as themolecule is too big. Dutrochet proved that osmosis is a vital process inbiological systems.Theprediction of this experiment is as follows: the author believed a decrease inwater concentration would occur within the potato pieces decreasing the totalmass. The definition of osmosis is water moleculesmovement across a semipermeable membrane from a high water concentration area toa low concentration area, predicting that decreasing water concentration in thepotato pieces the length and mass will decrease too. The higher the increase inthe sucrose concentration the greater the change in mass and length of thepotato pieces. At the end of this experiment the prediction is that the potatopiece in zero concentrate of sucrose will weigh the most because water willenter the vacuole through osmosis to dilute them as those cells have a largerconcentration in them.
Therefore, resulting in those cells becoming full ofwater and causing them to become turgid.Through this experiment, water molecules will pass through thesmall holes of the membrane in the potato piece. Which will pass in and out ofsolution and the potato piece. This depends on the concentration of the water/sucrosesolution.Molarity 0 of glucosesolution, in these pieces of potato the mass should increase as the water concentrationwithin the potato is lower than of that in the specimen tube.
Molarity 0.2 of glucose, thereshould be a slightly lower change than in the previous specimen, because of thelow amount of glucose used. Molarity 0.4 of glucose, thepotato pieces should decrease in weight as the water should transfer from thepotato into the glucose solution as it will be trying to obtain equilibrium.The author believes as thespecimens amount of glucose increases the mas of the potato will decrease dueto the process of osmosis.Methodobtain all items on theequipment lit as listed in appendix 1.Label all of the specimen tubes0, 0.
2, 0.4, 0.6, 0.
8 and 0.9.Fill each specimen tube usinga pipette with a solution as marked.
labelled 0 distilled water, labelled 0.28ml of distilled water and 2ml of glucose, labelled 0.4 6ml distilled water 4mlglucose, labelled 0.6 4ml distilled water 6ml glucose, labelled 0.8 2mldistilled water 8ml glucose, labelled 0.9 1ml distilled water 8ml glucose.Using cork borer, bore 6 equalpieces from the potato.Dry all pieces with a drypaper towel.
Measure and cut using thescalpel and ruler provide each into six 1cm pieces.Weigh every six pieces asaccurately as possible, then place each group of six into every specimen tube.When all six groups of potatopieces have been placed in the specimen tubes, time or 20 minutes.
Enter all results in the tableprovidedDrain, dry the potato piecesand re-weigh recording the result on the table.Calculate the change in massin grams and the % change by (change in mass / initial mass x 100)Enter all results onto agraph.Theexperiment showed that as the glucose concentration increased the mass of thepotato decreased. The results shown on the table inappendix one shows that when the concentration of sucrose is higher than thedistilled water, water will cross from the potato into the water through thesemi permeable wall to attempt to gain an equilibrium of water on both sides.
Showingthat osmosis will take place from the higher concentration to the lower concentrationof water. The higher sucrose in the solution the more osmotic activity tookplace causing a decrease in length and mass of the potato pieces. The potatopiece that was just in distilled water increased in mass and length because theconcentration of water was greater on the outside of the potato than withinbecause of starch held in the potato piece, drawing the water into the vacuolecausing it to become turgid. Translating these results onto the graph shown in appendixshows the increase and decrease in the mass of the pieces of potato.As stated within the hypothesis the prediction was correct, thatthere would be a decrease in length and weight of the potato pieces that werein the sucrose solution and a gain in weight, length of mass in the potatopiece in the distilled water. Meaning that when placed in a higher solution ofsucrose water was drawn from the potato pieces by osmosis into the solutiontrying to balance the concentration.