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Thread: help--? why use potato in osmosis experiment

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    Junior Member yinyin's Avatar
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    help--? why use potato in osmosis experiment

    Hey guys~~~
    i'm doing an osmosis experiment for my biology experiment~
    and i'm doing what factors affect the rate of osmosis. Ive look through the net and most of them use potato to carry out the experiment~
    But why potato?????
    Ive look through all the bio books i could find but still no solution~~~
    Please help~
    thank you ^_^
    Chasing after my dreams


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    salty rhia's Avatar
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    Re: help--? why use potato in osmosis experiment

    i don't really know: maybe because it retains its shape well when cut into a cube, is readily absorbent and probably also something to do with the colour. but don't worry too much about the potato, just... the experiment.

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    Ancient Orator Survivor39's Avatar
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    Re: help--? why use potato in osmosis experiment

    Maybe potato allow more water to enter its cells. It is easy to weight etc. It is cheap as well.

    PhD, University of Cambridge, 09-12
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    Re: help--? why use potato in osmosis experiment

    Correct Survivor "It is cheap as well"

    Im currently doing biology olympiad at Sydney Uni, we did osmosis yesterday with live human blood. I asked my lecturer why is the potato most commonly used, the answer was "because its cheap".

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    Banned The_highwayman's Avatar
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    Re: help--? why use potato in osmosis experiment

    could it be something to do with the starch in the potatoes?

    even tho that is more a diffusion thing than osmosis

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    Re: help--? why use potato in osmosis experiment

    potatoes act as the semi-permiable membrane.. allowing the solution outside enter ...
    the experiment is actually in the EXCEL textbook

    have a nice day ;]

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    Re: help--? why use potato in osmosis experiment

    Anything with a lot of water in its cells would work. Cucumber works a treat as would I imagine watermelon. Potato has the added advantage of having starch as its primary solute rather than a sugar. The sugar could readily diffuse out of the cells affecting/changing the osmotic pressure, but starch is made of larger molecules and won't diffuse through the membranes as readil, thus staying put in the cells.
    Cheers!

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    Re: help--? why use potato in osmosis experiment

    Actually, sugar is a collective term for carbohydrates. So starch, really, is a sugar.

    Sugars can be large or small. They don't have to be smaller than starch, which is a type of sugar.

    PhD, University of Cambridge, 09-12
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    Re: help--? why use potato in osmosis experiment

    Ahh, but if the sugars are the smaller di-saccharides or monosaccharides, they are water soluble and become even smaller, and they simply diffuse through the differentially permeable mebrane (cell membrane) producing isotonic solutions between the cytoplasm and the external environment - thus osmosis will no longer occur.

    By having larger sugar molecules the polysaccharides (aka starches), that are generally not water soluble, and so remain large, you will maintain a hypertonic solution for longer and thus osmosis will occur for a longer period of time - the starches won't diffuse out - hence use the potato.

    Cheers

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    Re: help--? why use potato in osmosis experiment

    Quote Originally Posted by yinyin
    Hey guys~~~
    i'm doing an osmosis experiment for my biology experiment~
    and i'm doing what factors affect the rate of osmosis. Ive look through the net and most of them use potato to carry out the experiment~
    But why potato?????
    Ive look through all the bio books i could find but still no solution~~~
    Please help~
    thank you ^_^
    I would assume they use potato because of the starch in it. Our osmosis prac involved dialysis tubing filled with starch and it was submerged in iodine solution. The iodine makes the starch turn a blue/purple colour and the iodine solution just becomes clear. Obviously due to osmosis. It seems like the easy solution to me.

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    Re: help--? why use potato in osmosis experiment

    Osmosis is a form of equalling out the concentration of particles. If you were to place a piece of potato in a beaker of salty water, the potato will either
    1. expel the water it contains in order to try and make the concentrations the same, and therefore become shrivelled and soft or
    2. take the salty water into its cells in order to equal the concentrations, and it will then expand and become hard and possibly even explode.

    I'm not sure which of the two it is, i learnt this from the analogy of a gold fish in salt water, so i assume its the same sort of thing. i don't think i need to mention the fate of the gold fish when placed in salt water........

    hope this has helped.

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    Ancient Orator Survivor39's Avatar
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    Re: help--? why use potato in osmosis experiment

    ange310. I think it's BOTH. You can't really have one and not the other.

    If you place a potato into highly concentrated salt water, water from the potato will move out, AND salt ions will diffuse into potato cells. The potato won't explode like you have suggested there.

    PhD, University of Cambridge, 09-12
    MSc, UNSW, 08-09
    BMedSc (Hons I), UNSW, 04-07

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