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right today we're going to look at the
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required practical for osmosis looking
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at the effect of different
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concentrations of solutions on some
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plant tissue our plant tissue being a
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potato and we'll talk more about the
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different concentration of solutions in
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a moment but what I want to do first is
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prepare my potato my plant tissue to do
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that we have a cork board this is going
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to allow me to take samples and potato
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that are all the same diameter and
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that's going to important so I can
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compare my results more easily so here
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is one cylinder now I'm going to cut
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three cylinders I'm just going to set up
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three different concentrations of
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solution today so one cylinder to
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cinders and my third potato
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cinder notice these are all coming from
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the same potato that should help keep my
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results more consistent each other
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easier for me to compare my results with
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each other now what I want to do now is
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just going to cut the ends off the ends
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of these as a potato skin it's going to
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move those they are impermeable they
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will not allow water into the tissue
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that's not what we're looking for this
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experiment all about water either moving
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into the plant cells or out of the plant
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cells and that's really what osmosis is
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I've now got where cylinders they are
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all the same length which is vital or
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approximately the same length so again
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helping me to compare my results later
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on but the instructions asked me to
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measure them into three centimeter
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lengths so I'm just going to go with
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that but they are about same length
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which is fine so the cut each one now
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I'm only using a ruler here not the most
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accurate way of measuring these but
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we'll get will go with it
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I'll talk about that in a moment I've
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got one
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- so that's again three centimeters get
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getting as close as I can to three
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centimeters while using a ruler three so
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I now have three as identical I can get
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them pieces of potato tissue
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well I now need to do is measure them
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very accurately as best as I can I'm
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going to measure both their lengths
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using a ruler and also their maths using
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the top pan balance so the ruler I can
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measure them and that one is exactly
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thirty millimeters so they are all
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exactly 30 minutes millimeters now I
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need to record those results I need to
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note sure that I know the length of each
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sender if they're different they're all
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the same in this case it doesn't really
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matter so need to recall those in my
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results table and then it's away their
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mass so on this balance what I'm using
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here is a balance that has two decimal
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places on it so it is accurate to a
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hundredth of a gram so I'm using a very
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high resolution top top and balance here
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to get very accurate result we're going
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to see probably very small changes in
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our mass here which is why we need to
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use this piece of equipment why it's
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appropriate and we have a mass of 2.92
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grams so I need to record that in my
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results table having recorded the length
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and mass this potato cylinder it now go
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to my boiling tube boiling tube I need
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to place some liquid into it now I'm
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going to start with distilled water so
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this is pure water so it's our first one
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so the puts in here I'm going to get
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down level I level of the measuring
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cylinder so I can very measure very
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accurately 10 millimeter milliliters of
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distilled water so go try to keep
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everything exactly the same between all
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my expense to help me compare my results
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there's my distilled water very
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important and I'll label this so I know
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what's in here
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so I can't mix up my samples which would
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be make it very hard to work out what's
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happened this experiment it's so hot at
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the moment I am going to add a bun to
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this not necessary if we only do this
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experiment for a short period of time or
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if the weather is not too hot this will
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help prevent any evaporation liquid out
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of the tube so this is my first sample I
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need to do that for my remaining two
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cylinders adding 0.25 molar sucrose so
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this is slightly sugary solution so it's
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got some sugar added to the water so
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this is sort of slightly sugary water
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and I'm going to add to another one 0.5
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molar sucrose this is a stronger
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solution of sugar and we need to see how
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these three solutions affect the potato
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now I have set some up earlier I did
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this yesterday allowing this to run for
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24 hours to help my results hopefully
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increase a bit so it should get bigger
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results and if I just do it for a short
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period time so Blue Peter moment income
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some that I made earlier so I no need to
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collect my results having left my
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samples overnight and so we're going to
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show you how to do that so get my
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distilled water sample first which is
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this one now I need to pour away the
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water I'm going to collect the potato
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cylinder into a sieve it's off camera
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but I'm just going to pour it into a
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sieve it's quite damp it's quite wet
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wetter than when I first got it from
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potato so we just remove the excess
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water on the outside of this that might
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affect the results quickest way to do
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that it's very quickly roll it onto the
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main paper towel it does not want to sit
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on the green paper towel that could draw
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liquid out of the tato which would
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affect my results but I have now removed
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the excess liquid so now measure my
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length again I'm using a ruler as I did
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before and has increased to 32
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millimetres length it's an increase of
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two millimeters there is another piece
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of clip we could use to measure length
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called vernier calipers these measure
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length more accurately so we could use
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these as an improvement to the expense
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but we're not going to do that today
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I now need to measure the mass of my
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potato after it's being distilled water
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for 24 hours on to the balance and it is
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now three point 1/2 grams that is that's
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actually increased from 2.9 for grams so
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again we have an increase here in in our
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results an increase in length and an
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increase in mass with distilled water
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these results must be written down in
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your results table so I've gotta click
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those results and I need to do the same
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for the other two solutions so they're
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0.25 molar sugar solution again so get
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pour away the water
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Claire toss cylinder quickly dry it
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measure the length it should thirty
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millimeters no real change there measure
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the mass which is three point zero six
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grams which is a very small increase
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yesterday's result before putting into
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the sugar solution was two point nine
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six grams so a very very small increase
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hit so having measured that one I need
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to write the results down and move on to
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my third sample which is the potato left
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in the strongest solution of sugar
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naught point five molar sugar solution
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so again collect my potato cylinder
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quickly dry on the paper removing excess
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liquid now I can actually feel this one
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it's quite floppy compared to the others
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which gives us a clue as well how
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results may look in a moment I measure
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the length hasn't particular changed may
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have gone down very slightly I can't
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really tell the actress's ruler so the
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length may decrease slightly I think
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that was about thirty millimeters hasn't
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really changed measure the mass and the
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mass is now two point six two grams
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there's a decrease yesterday I measured
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this at two point eight seven grams so
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it has decreased in mass so the other
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two samples so an increase in mass this
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one has decreased in mass so there's a
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difference there need to be thinking
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about why the two different results have
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occurred
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so we've now collect our results
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the next stage is to think about what we
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can do with that data so you need to
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calculate the difference in mass and the
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difference in length from yesterday to
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today you some of them the mass would
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have increased and for some of them the
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mass will have decreasing you to work
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that out okay so I've measured my length
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of my cinders yesterday
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and today I've made my mass my cinders
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yesterday and today my potato tissue and
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we've seen this in difference already we
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need to calculate the exact differences
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so what I'd like what you now need to do
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is take your length today your final
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length and minus the initial length to
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get a difference has it increased or
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decreased in length so you may get a
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negative number just decrease in length
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you may get a positive number is
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increase in length so you do the same
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for all three senators then do the same
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for mass so again mass today your second
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mass minus the initial mass and get
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looking you may get a positive number an
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increase in mass you might get a
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negative number a decrease in maths
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unfortunately because potations were not
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actually all identical to start now I
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did try very hard to keep them identical
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but they were not all the same mass at
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the start that makes it very hard to
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compare my results what I need to do is
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a little calculation that makes it much
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easier to compare my results a
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calculation called percentage change so
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now you've got your change in results
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you take that change in mass so your
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mass today
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minus your initial mass divide it by
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your initial mass multiply that number
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by a hundred and you have a percentage
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change so again if it is increasing mass
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to have a positive percentage increase
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and if you have decreasing mass with a
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negative percentage change and some
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potato did increase in mass and some did
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decrease in this nation okay you should
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be thinking about why that has happened
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if I did quite a few results more than
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I've done today you might get a graph
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that looks something like this
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so here's a what I've just sketched
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earlier it's not not particularly
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accurate but does show you the pattern
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you would
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expect to see so you can see here over
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here we've got a very pure water and our
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potato should gain a mass and as our
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concentration of sugar increases so as
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we add more and more sugar dissolve more
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more sugar in in the water
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we increase the sugar concentration you
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might talk about decreasing the
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concentration of the water we might see
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that the results decrease so initially
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our gaining mass gets less and less and
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less notice the language i've used there
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the gain in mass is decreasing
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we then get a point where our mass may
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or may not change we might not see that
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in our experiment but from a line of
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best fit we can see there's a point
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where there is no change in mass that's
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a very useful bit of information this
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tells you actually how much sugar is
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within the potato tissue itself though
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the the water concentration the sugar
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concentration within the sugar or in the
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potato is here so we can estimate that
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by where this line of best fit crosses
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this axis and then down here so down
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below this axis we have a loss of mass
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that is getting bigger and bigger so an
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increasing loss of mass so the more
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concentrated sugar the more water the
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more mass the potato should lose so
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that's down here so this is what's
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happening down here and that is osmosis
