13 Review the diffusion experiment involving starch and gluc

13). Review the diffusion experiment involving starch and glucose in the dialysis bag: a) What happened to the glucose? b) What happened to the starch? c) What happened to the water? d) Why did you use silver nitrate, BaCl2, Biuret and Lugol tests? e) Why did the weight of the dialysis bag change? f) How would your experiment change if we change the water in the beaker to 30% glucose and 60% starch?

I have a biology lab exam coming up this is one of the review topic questions. I would appreciate the help.

Solution

Starch molecules are large and are not able to pass through the semi permeable membrane of the dialysis bag, but glucose molecules are smaller. a) Glucose will pass through membrane and come out in beaker, provided its concentration is higher inside the dialysis bag, than outside. b)Starch molecules will remain inside the dialysis bag because of their large size. c) The total volume of water will remain the same. d) Lugol\'s Iodine (IKI) test is for the presence of starch: Iodine dissolved in an aqueous solution of potassium iodide - reacts with starch producing a deep blue-black color. Iodine molecules being small could pass inside the dialysis bag and react with starch inside the bag.This reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine. e) The weight of the dialysis bag will change due to reduction in total weight as it was before the reaction (glucose molecules came out).

f) If we change, the concentration of glucose and starch, glucose will flow from region of higher concentration to lower concentration and starch will remain as it was before because of its large size.