Example of a Good Lab Report Introduction Osmosis is a specialized case of diffusion that involves the passive transport of water. In osmosis, water moves through a selectively permeable membrane from a region of its higher concentration to a region of its lower concentration. The membrane selectively allows passage of certain types of molecules while restricting the movement of others. The solute concentration in the beaker is higher than that placed in the dialysis bag, and thus the water concentration is lower in the beaker than in the bag. This causes water to move from the bag into the beaker. This can be observed by adding a dye to the solution within the dialysis bag. Procedure The first step of this experiment is to fill an empty beaker with a 0.8M solution given by the instructor, followed by preparing a dialysis semi-permeable bag in which to measure osmosis. To prepare the bag, one must first gently loosen the two semi-permeable walls from one another to open what now looks like a flimsy tube. Gently, tie off one end of the tube tightly with the yarn. Next, fill the bag with a 0.2M solution given by the instructor and add one drop of green food coloring. Finally, tie off the open end of the bag as tightly as possible. Once the beaker and bag has been prepared, the next step is to weigh and record the initial weight of the semi-permeable bag. After completing this step, one is to place the prepared bag into the prepared beaker and wait for about eight minutes. After allowing the bag to sit inside the solution within the beaker, the bag is removed from the beaker and weighed again. Finally, this new weight is subtracted from the initial weight to show how much water the dialysis bag lost due to osmosis. Finally, to further prove osmosis occurred, one is to look at the remaining solution in the beaker. If there is a hint of green, then one can conclude that osmosis took place. Results and Conclusion The results of this lab mirrored what was to be expected. There are often several different types of molecules in a solution. The motion of each type of molecule is random and independent of other molecules in the solution. Each molecule moves down its own concentration gradient, from a region of its high concentration to a region of its low concentration. Though the net movement of molecules is down their concentration gradient, at any time molecules can move in both directions as long as the membrane is permeable to the molecule. Keep this in mind while you take a closer look at the beaker below. Some human errors that could have occurred would be mostly focused around opening and properly closing the dialysis bag. Some participants had issues in gently opening the bag, which resulted in a tear in the bag leading to a leaking of the 0.2M solution. Others did not tie of the bag securely enough which caused a greater outflow of the solution and therefore a greater loss of water. Questions 1. Will there be a net movement of water between two isotonic solutions? An isotonic solution occurs when there is an equal concentration of particles on each side of a semipermeable membrane. In order for particles to move, there needs to be a concentration gradient. A gradient occurs when there are unequal concentrations of particles on either side of a semipermeable membrane. Because there is no difference in concentration between two isotonic solutions, there will be no net movement of water between them. 2. Why don't red blood cells pop in the bloodstream? In order for cell to expand due to osmotic forces, it needs to be placed in a hypotonic solution. A hypotonic solution has a relatively low concentration of dissolved particles, when compared to the amount of dissolved particles on the inside of a cell. The liquid portion of the blood is considered to be isotonic to red blood cells. For this reason, there is no net movement of water inside or out of the cell, causing the cell to remain a constant size. Name: ________________ Period:________________ Yes (4 pts.) Yes, but (3 pts.) No, but (2 pts.) No (1 pt.) Accuracy The lab report The lab report The lab report did The lab report contained logical contained logical not contain any showed no attempt scientific thought. scientific thought, scientific thought, at scientific Each component but some of the but had some thought and contained accurate sections contained accurate contained many information. inaccurate information. instances of information. inaccurate information. Format All four One component is More than one components are missing from the component is clearly visible in lab report. missing from the the lab report. lab report. Creativity The lab report The lab report The lab report The lab report did contained creative contained some included very few not include any ideas that made the creative ideas, but creative ideas. unique or creative reader think about very little forward ideas. possible next steps. thinking was required. Writing Skills There are less than There are 5-10 There are 5-15 There are more 5 spelling, spelling, grammar, spelling, grammar, than 15 spelling, grammar, and/or and/or punctuation and/or punctuation grammar, and/or punctuation errors errors present in errors present in punctuation errors present in the lab the lab report. the lab report. present in the lab report. report. Timeliness The lab report was The lab report was turned in on time turned in late. to Criterion. A hard copy was also submitted in class.
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