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  • Level: GCSE
  • Subject: Science
  • Essay length: 5348 words

Looking at how concentration affects the movement of water particles through a partially permeable membrane

Extracts from this essay...


Investigating how Concentration affects Osmosis? Aim Looking at how concentration affects the movement of water particles through a partially permeable membrane Prediction I predict that when the potato is submerged into highly concentrated sugar solution the mass will decrease. However, when the potato is submerged into plain water the mass will increase. I predict that relationship between the pure water will be linear however the relationship between the sugar solution will be a smooth curve. Scientific background Diffusion Diffusion is the process by which a substance moves from a region of high concentration of that substance to a region of low concentration of the same substance. Diffusion occurs because the molecules of which substance s are made in random motion (kinetic theory). The rate of diffusion depends upon: 1. The concentration Gradient - The greater the difference in concentration between two regions of a substance the greater the rate of diffusion. Organisms must therefore maintain a fresh supply of a substance to be absorbed by creating a stream over the diffusion transported away. 2. The distance over which diffusion takes place - The shorter the distance between two regions of different concentration the greater the rate of diffusion. The rate is proportional to the reciprocal of the square of the distance (inverse square law). Any structure in an organism across which diffusion regularly takes place must therefore be thin. Cell membranes for example are only 7.5nm thick and even epithelial layers such as those lining the alveoli of the lungs are as thin as 0.3µm across. 3. The area over which diffusion takes place -The larger the surface area the greater the rate of diffusion. Diffusion surfaces frequently have structures for increasing their surface area and hence the rate at which they exchange materials. These structures include villi and microvilli. 4. The nature of any structure across which diffusion occurs - Diffusion frequently takes place across epithelial layers or cell membranes.


Use the same apparatus with the same configuration and position. 4. Doing the experiment on the same day therefore, constant environment (i.e. not one day cold, second day hot) 5. Allowed each strip of potato the same amount of time. 6. I will use the same cork borer to take each piece of potato, otherwise the investigation will not be a fair test. The factors, which will affect my investigation, are: 1. Potato weights (i.e. the weights may not be precisely the same). 2. Diameter of the potato. 3. Thickness of the potato. 4. Type of potato (whether the type of potato absorbs well or doesn't absorb well). I will control them by checking to see that the same potato is used therefore the weights will be almost the same and notify what type of potato it is. I will also use the same cork borer therefore the thickness of the potato will be the same. The factors, which I am unable to control, are: 1. Fluctuation in the potato strips. 2. The uniformity of the potato strip diameter. 3. Holes on the potato. 4. The condition of the potato throughout the strip (I.e. one end may be quite flaccid whilst the middle and the other end could be turgid). The apparatus or source of evidence will make my measurements and evidence accurate as when I take the readings from the weigher, the readings will be digital, therefore I will have a precise digit, however the digits fluctuated a bit but settled within a few seconds. The measurements of the potato strip length were precise and accurate as the calculator showed whether the number was positive or negative allowing me to say whether the mass increased or decreased. Safety The safety precautions which we might have to be aware of is: * Not to touch the potato strips when the experiment is in process otherwise it may cause a differ in the results.


5. I made sure I did my experiment on the same day, constant environment (i.e. not one day cold, and the other day hot) 6. I made sure that the weights of the potatoes were reasonable the same. 7. I also made sure that the total volume in each test tube was 20ml therefore the volume will be same through out the whole experiment. 8. I also made sure that each test tube had 20ml of solution so that firstly the potato will be completely covered, (that one wont have a larger surface area covered than another) and secondly there will be a ratio of showing how many parts were pure water and how many parts were the concentrated sugar solution. I think I have collected enough evidence to support my conclusion from my trial and actual experiment however if I had to improve on my results or find more evidence I would do another trial experiment to find more precise length ranges. To do this I would use smaller increments in length. This would help me to verify my final result with more precision and accuracy. The difficulties I had whilst carrying out my investigation was ensuring that I did not run out of time and, as group coordinator that everyone in the group understood, and knew what to do. Typically I ensured that everything was weighed correctly, recorded and a drawing a suitable table (i.e. concentration of solution (1M), Time left for (minutes), Mass of the potato before, Mass of the potato after and Mass gained or lost). If I were to repeat this investigation again the things I would change in my method would be to use a better weigher that would give more accurate readings; use better pieces of potato strips that was more in a straight line and had no holes because a small hole could represent 3mm making my investigation invalid and therefore presenting that my results were incorrect. Overall I would do more experiments, if I had more time, and so obtain more evidence to support my conclusion.

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