Australia's Science Forum

Hiya,

a cheap & cheerful tip for digestion & absorption pracs....instead of dialysis tubing, you can use tiny zip-lock bags.

Livingstone International have them in all sizes, 40mm x 75mm $3.50 for a box of 1000, 50mm x 75mm $3.65 for a box of 1000.
They're semi-permeable & the kids don't have trouble like they do with the dialysis tubing

wow! thanks for the tip, will try that next year, much cheaper

Do you mean for osmosis and diffusion??

We use dialysis tubing for digestion prac with starch and sugars.
Great tip. Will make life a lot easier.
Lada

Do you use enzymes??

Yes, we use amylase to break down starch into simple sugars.
Use iodine to check for starch and benedicts to check for sugars.
Lada

Bindibadgi,
would you have catalogue number for those bags. Cannot find them
Thanks,
Lada

Freezer bags from the supermarket work also.
Even cheaper

40 x 75 cat # is BPEZ040X075
50 x 75 cat # is BPEZ050X075

Do a search for 'zip-lock' & it'll show all the sizes...the biggest is 360mmx x400mm!

Ditto what Lada said too, we get the kids to set up 3 bags: glucose, starch, starch+amylase all in beakers of water....then test for sugar & starch with the benedict's & iodine straight away, & 24 hours later (I always spike the beakers with a little glucose too of course )

A cute little visual demo to do while they're getting their bags & beakers set up is to fill a bag with some starch solution & pop it in a beaker of diluted iodine. Within 10-15 mins the starch in the bag's turning blue-black, but the iodine in the beaker stays the same.

Thank you will take that on board, l am new to this site but am loving reading all your ideas and saving a heap of them.

HI guys
I tried this out for the prac we do, with starch and glucose solution inside the dialysis tubing, in a beaker of iodine solution. Iodine moves into the tubing, glucose moves out. With the snap lock bags the starch/iodine bit worked really well but the glucose didn't transfer at all. I was using just some Hercules ones from the supermarket rather than Livingstones ones. I even left it over night and no glucose was detectable. Is it just that the bags are different?

Could be. For this to work they have to be permeable (semi-permeable).
Lada

So the glucose definitely works with the Livingstone ones? Maybe I'll have to order some. If I can get that bit to work it is so much easier than the dialysis tubing.

Hey guys - I have done this with freezer bags, not zip-lock bags! Not to say that the zip-locks don't work, just that the freezer bags do work, especially for the starch/iodine exp.

Just bumped this page again.

Thanks Labbie