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Why does the concentration of both glucose and sucrose decrease in this bag?
Hi this is a biology question my wife doesn't understand:
A 2% glucose and 3% sucrose solution is added to a bag made from a membrane that is permeable only to water and glucose. The bag was then placed in a beaker of water containing a 1% glucose and 1% sucrose solution. What would happen to the concentration levels of sucrose and glucose inside the bag after one hour? (My wife thinks that sucrose is still going out of the bag somehow. I don't think so though, but I'm not a bio expert. I theorize that with more "elbow room" after the glucose has diffused evenly, the sucrose has also spread out in the bag and thus diffused).
Hi the first answer given below by the Bio-Instructor makes sense to me.
However, my wife's Bio-Text-Book says the correct answer is this:
Both glucose and sucrose concentration would decrease in the bag.
In particular what we need to know this:
The question says the "Membrane is only permeable to water and glucose", but is sucrose still going out somehow? , or else, how is the concentration of sucrose going down in the bag? (like the Text Book Answer Key Says).
2 Answers
- 1 decade agoFavorite Answer
Ok, lets recap. You have a selectively permeable membrane (the bag) that contains pores large enough to allow glucose to pass through, but too small to allow sucrose (a large molecule) to pass through. There is 2% glucose (98% water) and 3% sucrose (97% water) in the bag. The bad is then place into a beaker containing 1% glucose and 1% sucrose (99 % water). Since the sucrose can not pass through the bag because it is too large the concentration of sucrose in the bag will not change, but water will move from the beaker (99% water) and inter the bad (less then 99% water), because water molecules are small enough the diffuse through the bag.
Now the glucose, since the glucose is a small enough molecule to move through the bad it will diffuse from where it is high in concentration, inside the bad, to where it is low in concentration, outside fo the bad, until it reaches equilibrium, 2% glucose inside the bad and in the beaker. In this case the sugar movement is based on their molecular size and concentation differences.
I hope this helps.
Source(s): I'm a biology instructor... - 1 decade ago
The concentration of glucose and sucrose decrease due to osmosis. As you mention that the bag contains a solution of 2% glucose and 3% sucrose and that of the solution in the beaker contains 1% glucose and 1% sucrose, this makes the solution in the bag a hypertonic solution, i.e., a solution of high concentration or less water content and that of the solution in the beaker a hypotonic solution, i.e.. A solution of low concentration or high water content. As we know, in osmosis, movement of solvent molecules is from hypertonic to hypotonic solution through a semi-permeable membrane, the concentration of the hypertonic decreases. In your case, the 2% glucose and 3% sucrose moves to the 1% glucose and 3% sucrose solution until an equilibrium is achieved between the two. As a matter of fact, sucrose in the bag will have a higher rate of osmotic diffusion as it has a higher concentration than glucose. Also the difference in concentration between the glucose in the bag and beaker is 1% while that of sucrose is 2%. So sucrose in the bag loses its concentration more rapidly as compared to the glucose in the bag.
