Brief Summary
This video explains the dialysis tube lab experiment, focusing on the principles of osmosis and diffusion. The experiment demonstrates how different-sized molecules move across a semipermeable membrane, mimicking a cell. Key observations include the movement of glucose and iodine, the immobility of starch, and the overall change in the bag's weight due to water movement.
- Osmosis involves the movement of water from an area of high concentration to low concentration.
- Diffusion involves the movement of particles from an area of high concentration to low concentration.
- The dialysis tube acts as a semipermeable membrane, allowing certain molecules to pass through based on size.
The dialysis tube lab explores osmosis, the movement of water, and diffusion, the movement of gases and particles. The experiment uses a beaker containing a dialysis tube, which acts as a semipermeable membrane. The beaker is filled with water and iodine, while the dialysis tube contains glucose (15%) and starch (1%). Initially, the water is brown due to the iodine, and the solution inside the bag is clear, possibly slightly cloudy.
The experiment involves observing changes over 30 minutes. Glucose molecules are small, whereas starch molecules are large polysaccharides. The dialysis tube, like a cell, selectively allows molecules to pass through based on size. Given this, it's expected that glucose will move out of the bag due to its smaller size.
After 30 minutes, the water outside the bag tests positive for glucose, indicating that glucose has moved out of the bag. The bag's contents turn black. This colour change occurs because iodine diffuses into the bag and reacts with the starch inside. Starch remains inside the bag because it is too large to pass through the semipermeable membrane.
Iodine diffuses into the bag because it is a small enough particle. The black colour inside the bag confirms the presence of both starch and iodine. This demonstrates diffusion, with glucose moving out and iodine moving in, based on their respective sizes.
The bag's weight increases, indicating water has moved into it. Inside the bag, there's more solute (glucose and starch), meaning less water. Outside, the beaker is full of water with very little solute. Water moves from high to low concentration (outside to inside), a passive transport process. This influx of water causes the bag to swell, a condition known as hypotonic, where water moves into the cell.
The solution outside the bag is hypotonic, meaning the water concentration is higher outside than inside, causing water to move in. This experiment exemplifies both osmosis and diffusion without any energy input, illustrating passive transport.
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Transcript
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0:00 [Music] okay so we want to take a look today at explaining the dialysis tube lab and in the dialysis tube lab we are really looking at two major major phenomena two major concepts and that is osmosis and diffusion taking a little samosas infusion and if you remember back from our notes osmosis was the movement of water and diffusion is movement of gases and particles so let's take a look at the actual experiment so in this experiment we have a beaker and in the
0:45 beaker we have a dialysis tube and that represents a semipermeable membrane and then we put water and we put iodine out here and we'll take a look at that in our data table as to what color that may turn inside we put glucose and we put starch approximately a 15% glucose a 1% starch that's really not that important but it kind of gives you an idea of what's inside of the bag so if we look at the preliminary so the initial colors of everything that's going on we see that in the water it tends to be that Brown the brown color that the iodine
1:31 turns the water on the inside inside the bag we see it's clear if not maybe just a little cloudy but it's it's a whiter color so we take a look at this experiment and again we see that though the water is gonna be our brown color our bag is gonna be clear and cloudy as we let this sit for about 30 minutes we are gonna look at two different two different phenomena here let's look at the glucose and the starch in here the glucose and the starch obviously if we remember back from carbs are two different sizes glucose is rather small very very small you put several hundreds and thousands together and we can make starch so starches are big polysaccharide so if we
2:17 think about this a dialysis tube is just like a cell it's semipermeable it means it allows things to move in and out and it chooses what's gonna move in and out in this case it's gonna allow certain molecules to move in and out based upon size so knowing that we know glucose is a lot smaller we're gonna see glucose start to come out in the bag let's take a look at the final results so that you can see so we can parallel back to what we have when we look at the water after at the very end the water is still brown but it tests positive for glucose we put a glucose test strip in there it'll actually test positive whereas over here it was negative for glucose so that's a big a big conclusion
3:02 the big piece that we wanted to take a look at and then really remember is the idea that somehow glucose has gotten out of the bag and into the water we now take a look at the bag and it's really amazing to see it the bag turns black so what could be turning the bag black we've discussed already that based upon size glucose moves out of the bag that would be diffusion that's movement of a particle so glucose is moving out in the bag which is why the water tests positive for glucose at the very end but starch does not move out here how do we know there's a very important reaction when you mix starch and you mix iodine and you put those two together they make a black color so if the starch were to move out of the bag then the water out
3:49 here would be turning black and it didn't it stayed brown it stayed the color of the iodine so we know that the starch could not move out of the bag which means it was too big of a molecule and that's going to allow this right here to stay our brown color and test positive so now we wonder why did the bag turn black we know that iodine and starch when they meet that turns black but we have the semipermeable membrane looking at this the starch couldn't leave the bag so it stays in but the iodine was able to diffuse in the iodine is a small enough particle as well that you can diffuse into the bag and then it's turning the bag black because that starch and iodine is mixing together so in here we look at this and we see diffusion we have diffusion of glucose out we have
4:34 diffusion of iodine particles in if you were to weigh this bag initially let's say the bag was five grams after we put everything in and of course that's an arbitrary number it's not returning number in that you know I don't it's not the exact number but if we notice if we do our final here we'll see that it maybe goes up to say 12 grams what is causing that gain in water well think about this out inside the bag we have all the school codes out of the starch so talking just in terms of water potential we have more solute which means we have less water inside out here we have a whole beaker full of water and very little substrate very little
5:20 particles or substances so our water is more concentrated outside of them cell than inside the cell which means if we know and I'm going to just going to draw this as sort of a kind of a thing here that if let's give it a number let's say that's five percent water on the inside and let's say it's 20 percent water on the outside again just choosing numbers to show our relationship we know that water moves from high to low concentration that's why it's passive transport so the water is going to move from outside into the cell this causes the cell to swell up which we learned last week or just call it site tolerance
6:05 in the last class and that is where the cell is gonna swell and eventually burst this process where water is more concentrated on the outside than the inside is called what kind of solution that's right is called hi-ho tonic hypotonic remember if you were remember the word hippo hippos are big and fat and taking water water is moving into the cell the opposite of hypotonic of course is hypertonic and that's where the water would have been moving out of the cell but we don't have that situation so this is a quintessential case an experiment that really does show a lot of initial movement of particles for diffusion a movement of water to balance out and
6:52 maintain that homeostasis at equilibrium through a hypotonic where the water is moving in but really just a good example of seeing both osmosis in diffusion happening and yet we didn't put any we can put any energy this is why is passive transport so that is the dialysis tube lab and I hope that that helps
