The purpose of lab 1A was to demonstrate what a selectively permeable looks like. The independent variable was the solution we put in the dialysis bags. The dependent variable was the color that the solution turned. This demonstrated selective permeability because we could actually see that only iodine could come through the bag.
The purpose of 1B was to provide an example of osmosis. The independent variable was the solution that we put in the dialysis bag and the dependent variable was the weight when the experiment was done. This shows osmosis because we could see how things went from a high concentration to a low, which caused the change in weight.
The purpose of 1C was to show how water potential works. We could see how the potatoes swelled or shrunk. The independent variable was the solutions that we put the potato cores in and the dependent variable was the weight of the potato cores.
The purpose of 1E was to show how the cells react to diffusion and osmosis. We could see how the cells swelled or shrunk.
A selectively permeable membeane allows certain molecules in and out of the cell. Molecules will diffuse from a higher concentrition to a lower concentration until the each equilibrium-the point that there is equal quantities on both sides-and there will no longer be any net movement of particles. Osmosis refers to the diffusion of water and dialysis refers to the diffusion of solid particles. Water potential is a property which predicts which way water will flow. It is determined by solute concentration and pressure. Water will move from areas of high water potential to low areas of water potential.
In this portion of the experiment we took a dialysis bag and filled it with sugar water in the cup. We took this bag and placed it in a iodine-water mixture. We waited for around 25 minutes and took out the dialysis bag to see the new concentration of the sugar water. The dialysis bag acted as a semi permeable membrane.
In this part of the experiment we took 6 dialysis bags and filled them with different concentrations of sucrose. We placed each bag in a cup of water and proceeded to wait for 30 minutes to see if the mass of the bags had changed. Again, the dialysis bag acted as a semi-permeable membrane.
We used a cork borer to cut 24 potato cylinders (4 per cup). Then we weighed and recorded the 4 cores that went in each cup. Each cup had a different solution in it. After letting the potato cylinders sit for a while, we pulled them out and weighed and recorded them again.
In this part of the experiment we looked up picture for onion cells to see when it would look like in Hyper, hypo and iso tonic environments.
1a Before the dialysis bag was dropped into the iodine solution, it tested negative for glucose. The bag was clear and the iodine solution was scarlet. After letting the bag sit, it turned a black/blue color and both the bag and iodine solution tested positive for glucose.
1b For each bag, the mass increased after it was dropped in the water. The change in mass varied from 3.16% to 16.88%.
1c For every bag, the mass increased after the were left to sit in the sucrose solutions. For the most part as the molarities of the sucrose went up, so did the weight that the bag gained.
Graphs and charts
In these experiments we demonstrated how semi permeable objects work like the cell membrane. As well as presenting how a semiPermeable membrane works, we demonstrated osmosis, water potential, and how cells react to diffusion and osmosis. We saw in experiment 1a that the dialysis bag only let in glucose into the bag, instead of letting all parts of the iodine in. The strips changed to show that glucose was in fact present. In experiment 1b when we took the dialysis bags and filled them with solutions with different levels of sucrose, and we saw that the higher the molar it's of sucrose, the higher the mass went up. In 1c, where we took the potatoes, we saw that the potato cores gained in Mass while it sat In the sucrose solutions. In 1e, we looked at photos of onion cells in hypertonic, isotonic, and hypotonic solutions. This let us see how our cells react to the different environments around it.
Throughout all the experiments, there wasn't a question that we were to answer. They were more to demonstrate the concepts we learned in class. 1A showed how a membrane can be selectively permeable by only letting iodine through. 1B showed how water flows in osmosis. 1C showed what water potential is, using the potato as an example. 1E gave an example of how diffusion and osmosis affects the cells in our body.