biology- osmosis investigation

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Preliminary work

Before I started my investigation I spent time deciding how I was going to find the results. I looked at various possibilities for variables and how I could keep these the same. I also did small separate experiments to make sure that the measurements that I had chosen were suitable in comparison to what was being tested.

It is important to do preliminary work so that you have a clear method, and know what you are specifically what you are doing for each part of the experiment. This is to prevent too much variation between the results data due to different methods (even if only slightly) when carrying out the experiment.

The preliminary work informs my plan of the method and also checks that the method is a reachable one that it can be carried out with my facilities. The preliminary work has showed me the measurement I need to use and the apparatus will need. Here are the questions that I asked myself when doing the preliminary work:

  • How to cut the chip? Out of a range of possible apparatus for cutting the potato I decided to use a cork borer. There was also a range of sizes that the cork borer came in I decided to use the size 6 version. This cut a cylinder of the potato that i called a chip. I then measured these and cut them using a scalpel so that they were 5cm in length. This made all the potatoes the same size.
  • The size of the chip? The size of the chip was determined by the size of the cork borer and was then cut down so that each chip was a cylinder 5cm in length. This had already been decided once I knew how to cut out the chip
  • Length or mass? I decided to measure the chips in length rather then mass because when i tested trying the get the mass the same some were the same mass but looked different sizes which made it very difficult to judge. The benefit of judging by length is that it meant that the surface area of each chip if accurate should be the same.
  • Type of potato? Although i had to use more than one potato for the experiment because they were not big enough for all the chips i used the same type of potatoe, which was the way to keep the chip types the same. I standardised the type of potatoes I used by using only “King Edwards”.
  • How much liquid is needed? When I was deciding how much liquid was needed for the experiment I decided that it must be enough to completely submerge the potato chip. I decided to use 30cm3 of the liquid because this was enough to submerge the potato chip but was not too wasteful at the same time because it is pointless to use too much exceeding the need of the whole chip being submerged.
  • What consistencies of sucrose are needed?  I decided to use 6 different concentrations of sucrose. There concentration was measured in molar. The first concentration was distilled water, which was the control to compare the other results to. The other measurements were 0.2 molar, 0.4 molar, 0.6 molar, 0.8 molar and 1.0 molar.
  • How long should you leave them? I decided to leave the chips in the sucrose solutions for 24 hours. Although this was a very difficult because it was very difficult to control the time and i had to try and arrange it around the school day. I tried to collect the results as close to as possible to 24 hours.
  • Blotting? I decided to blot the potatoes with filter paper before weighing their mass after the 24 hours in the sucrose this is because I didn’t want any excess water that hadn’t actually gone through the potato’s partial membrane to upset the results.
  • Temperature of the sucrose? The sucrose (and distilled water) were all kept at room temperature this was important because it the temperature was hotter that it would have caused the particles to move around more and faster possibly speeding up the experiment and if all the temperatures were different but this was not the variable you wanted to change then the results would not be very accurate.
  • How can I ensure reliability?  With this experiment I decided to make the results more reliable because I decided to repeat the experiment 3 times. I will then take and average from theses individual experiments so that my results are more reliable.
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Main Experiment

Aim: to investigate the effect of osmosis on potatoes when places in different concentrations of sucrose (sugar solution).

Apparatus

  • Cork Borer (size 6)
  • Potatoes (King Edward)
  • Sucrose (30ml of each) Concentrations (molars) – 1.0, 0.8, 0.6, 0.4, 0.2,distilled water
  • Measuring cylinder
  • 6 test tubes
  • Beaker
  • Pipette
  • Ruler
  • Scales
  • Funnel
  • Tile
  • Scalpel
  • Stopwatch
  • Test tube rack

All of the above x3 for the repeat experiments

Method

  1. My first step was to cut out the chips using the cork borer this was done using the method that I devised when doing ...

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*** An okay attempt at the investigation but it is still largely incomplete. The aim of the investigation was investigate the effect of osmosis on potato chips at varying concentrations, but there was no analysis of the results. The experiment seemed to have been completed accurately but the results were not recorded in an appropriate fashion to clearly show the reader how much length / mass had been gained or lost. The graphs reflected this, it was unclear what they were showing. The analysis should have gone through the effect each concentration had on the potato chip and this should have been explained in an evaluation using the theory of osmosis. The theory that was included on osmosis was very good but it was not linked to the results; the control of the variables at the start of the report was also very good.