tissue water如何测定

The Water Potential of Plant Tissue Aim: To find the water potential of plant tissue by investigating the effects of varying concentrations of sugar solutions on the amount of osmotic activity between the solution and potato cylinders. Hypothesis: Osmosis is defined as the net movement of water from regions of high water potential to regions of low water potential. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other. Prediction: Pure Water has the highest water potential (zero). For this particular investigation I think that the lower the concentration of the sugar solution in the test tube the larger the mass of the potato will be. This is because the water molecules pass from an area of high sugar concentration, i.e. in the water itself, to an area of low concentration, i.e. in the potato chip. Therefore, the chips in higher water concentrations will have a larger mass than in higher sugar concentrations. Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what makes the green parts of the plant "stand up" into the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The contents of the potato cells shrinks and pulls away from the cell wall. These cells are said to be plasmolysed. When plant cells are placed in a solution, which has exactly the same osmotic strength as the cells, they are in a state between turgidity and flaccidity. This is called incipient plasmolysis. Incipient means 'about to be.' Variables: The independent variable of this investigation is the molarity of the sugar solutions. I will be mixing many different concentrations of solutions and errors in the making of these concentrations can occur. The dependent variable of this investigation is the change in mass of potato. This should occur by changing the independent variable. Other Variables include: · Solution concentration Surface area · Solution volume · Duration of experiment · Temperature · Solution · Conditions which experiment is kept in Preliminary Results These results were achieved by putting potato chips in different concentrations of sugar solution. Concentration of solution Mass Before Mass After % Change inMass 0.00m: 1st attempt 1.66 1.74 4.819277108 2nd attempt 1.58 1.66 5.063291139 0.25m: 1st attempt 1.7 1.62 -4.705882353 2nd attempt 2.06 2.07 0.485436893 0.50m: 1st attempt 1.69 1.62 -4.142011834 2nd attempt 1.78 1.67 -6.179775281 0.75: 1st attempt 1.76 1.6 -9.090909091 2nd attempt 1.71 1.56 -8.771929825 1.0m: 1st attempt 1.74 1.59 -8.620689655 2nd attempt 1.4 1.25 -10.71428571 Percentage change Concentration Average % change 0.00m 4.94128412 0.25m -2.11022273 0.5m -5.16089356 0.75m -8.93141946 1.0m -9.66748768 These preliminary results gives me the overall impression of the change in mass, gain and loss when placing potato chips in varying concentrations of sucrose solution. To carry out this investigation I will use the following apparatus: · Sucrose Solutions · 2 different sized measuring cylinders (10ml and 25ml) - More accuracy · Ceramic Tile - To cut potato on using scalpel · Ruler - To Measure potato chips · Scalpel - To cut potato into appropriate sizes · Forceps - to hold the potato chips · Stopwatch - to measure the time the experiment is taking accurately · 10 boiling tubes - to place potatoes and sucrose solutions in · A boiling tube rack - to hold boiling tubes · Potato borer - To cut pieces from potato - more accurate than cutting · Scales - To measure mass of the potatoes (g) · 2 Large Potatoes Originally, when I conceived my plan, I had intended to only use 5 different concentrations of salt solutions and only have the tubes of potato in the concentrations for 20 minutes. Since reading up on the biology internet sites (www.Studentcentral.com and www.biologybook.com) as well as many other biology books which refer to osmosis, I believe using 10 concentrations of sugar solution and one of water would give more reliable and accurate results. I will also be leaving the potatoes in the solutions for 30 minutes instead of twenty. This reduces chances of anomalous results. This is the method I have planned to use to achieve the experiments outcome: · A range of sucrose sugar solutions will be prepared with concentrations 0 molar, 0.1 molar, 0.2 molar, 0.3 molar, 0.4 molar 0.5 molar, 0.6 molar, 0.7 molar, 0.8 molar, 0.9 molar and 1.0 molar. · Sections of potato will be taken from the potato by a potato borer to a ceramic tile, then cut using a scalpel and will be measured using a ruler. For this experiment I am going use potato pieces of 2cm length. This part of the preparation must be done very accurately as a change in the surface area may allow more or less osmosis to occur. · After this the potatoes are going to be weighed on scales with its measurement in grams. · Three chips will be placed in each boiling tube each time so that I can take an average for each tube. Before pouring in different concentrations of sugar solution, I will label each tube so as to remember when I have poured the solutions in, which solution I have · I will then pour 10 ml of each concentration of sugar solution into the selected boiling tubes. · I will then observe for 30 minutes before removing the potatoes from the solutions. I will then measure and weigh them. I will then write all results in a table like this: All length and masses in this table are averages taken from three different potato chips per solution. Molarity of Sucrose Solution Starting mass Starting Length Mass 10min Length 10min Mass 20min Length 20min Final Mass Final Length 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 To Make this a fair test, all Variables (except the independent variable), must be kept constant to allow for a fair test. Some of these are: · The length, mass, diameter of the potato tubes. · The volume of solutions used, giving consistency · The temperature, increasing temperatures lead to an increase in kinetic energy and thereby the rate of diffusion will increase. · The time the potato tubes are left in their solutions. More exposure equals more osmosis taking place. · To follow consistency, the same apparatus used. · It is best not to touch the potato to avoid contact with cell surface membranes, so I will use forceps. When working on an experiment, it is easy forget how to handle things safely and conduct yourself in a safe manor. · Unused surfaces to be kept clear during the experiment. · Wash your hands before and after using the lab · Proceed with care when working with glassware and electrical light sources. · Always take care when handling chemicals.