Monday, October 21, 2013

Diffusion Osmosis Lab

Purpose-
1A) This part of the lab tested permeability. The lab used a glucose/starch solution inside a dialysis bag submerged in an iodine solution (independent variables) to determine whether the dialysis bag was selectively permeable. This was determined by the color of the solutions in the bag and inside the beaker (dependent variables) after 30 minutes of the bag being soaked in the IKI.

1B) In this part of the lab we tested the net movement of water through a selectively permeable surfaces that contained hypertonic and hypotonic solutions by osmosis. The lab used dialysis bags filled with solutions of different molarities (independent variable) submerged in distilled water to figure out how much osmosis would occur with the hypertonic versus the hypotonic solutions. This was determined by the mass of the bag (dependent variable) after being submerged in the water for 30 minutes.

1C) The main concept tested in this part of the lab was water potential. Potato cores were submerged in solutions with different molarities (independent variable) in order to determine the water potential of a potato cell. The mass
of the potato cores (dependent variable) after they were soaked in the solutions overnight revealed the water potential of the cells.

1E) The concept tested is plasmolysis. The lab uses onion cells submerged in solutions of different concentrations (independent variable) in order to determine how much the cell wall would retract from the cellular membrane (dependent variable) as a response to the different concentrations.
Introduction-

1A) Diffusion is the random movement of the molecules from an area of higher concentration to an area of lower concentration. Osmosis is the diffusion of water through a selectively permeable membrane (a membrane that allows diffusion of certain solutes and water) from a region of higher water potential to a region of lower water potential. Water potential is the measure of free energy of water in a solution.

1B) A hypertonic solution is the one with less solute. A hypotonic is the one with more solute. Whether the solution is hypertonic or hypotonic determines the net movement of water.

1C) Water potential has 2 components: a physical pressure component and the effects of solutes.

Water Potential = Pressure Potential + Solute Potential

Water will always move from an area of higher water potential to an area of lower water potential.

1E) Plasmolysis is the shrinking of the cytoplasm of a plant cell in a response to diffusion of water out of the cell into a hypertonic solution surrounding the cell membrane. During plasmolysis the cell membrane pulls away from the cell wall.

Methods-

1A) We took a dialysis bag and filled it with a solution made up of 15% glucose and 1% starch. Then we soaked it in the iodine solution. We used the urine strips to measure the glucose content, and then recorded the initial content and color. It was left to sit for 30 minutes . After, we measured the glucose again and recorded the results.

1B) We took 6 dialysis bags. Each bag had a different amount of sucrose in it, the sucrose went up increments of .2 mole . The first bag was distilled water and had 0 M. The sixth bag had 1.0 mole sucrose. After, the bags were filled with the sucrose they were weighed. Then each bag was put in beaker filled about 2/3 of the way with distilled water. We let the bags sit in the beaker for 30 minutes. After 30 minutes was up, we dried the remaining water off the bag and weighed them again. Last, we recorded the weight change.

1C) In this experiment we cored a potato to get 24 different pieces. We split up the potatoes between 6 beakers. Each beaker got 4 potatoes. After the potatoes were cut and split up, we weighed each group of potatoes. Then they were placed in their assigned beakers. Each beaker was filled with a different concentration of sucrose. The first beaker was distilled water and the beakers concentration of sucrose went up by .2 mole. The last beaker was filled 1.0 mole of sucrose. The beaker were left to sit for 1 day. The next day, we took the potatoes out of their beakers and dried them off. Then we weighed the potatoes again and recorded the data.

1E) In this experiment we cut 3 small pieces of onion epidermis. We observed the pieces of epidermis under 100x microscope. Then, we added 2 to 3 drops of 15% NaCl to the onion epidermis. Finally, we flooded the onion cell with fresh water, and then looked at the change in the cell under the microscope.

Data-
 



Discussion-

1A) By emerging the bag of 15% glucose & 1% starch into the beaker of H2O & IKI solution, the weight of the bag increased because iodine passed into the bag. This bag is a perfect demonstration of a selectively permeable membrane: it only lets glucose and iodine pass. Starch is not allowed to leave the bag, therefore there is no color change in the iodine solution. After letting the bag sit in the iodine solution for approximately thirty minutes, iodine eventually makes its way into the bag through its selectively permeable membrane, which explains the color changing from colorless to a deep blue. There was no chemical or color change in the iodine because the starch molecules were too large to fit through the membrane pores. Starch could not leave the bag and it's the only substance that would've effected it.IMG_2878.jpg
 IMG_2811.jpg Dialysis bag after sitting in the solution for 3o minutes.

1B: Dialysis Bag
Sugar molecules take up the most room in the bag, which leave a small amount of 'space' for water. Because water always strives for equilibrium, it constantly tries to diffuse into the bag, causing the bag's mass to increase. Osmosis occurs in this experiment because it is a type of passive diffusion, meaning it happens on its own. Water travels in and out of the membrane pores with the help of aquaporfins to reach equilibrium.When the bag of distilled water was emerged in distiller water, its mass went down because water was striving to reach equilibrium. It left the bag trying to equal it's self out, doing so by passing through the membrane pores. In an ideal trial of this experiment with no traces of sugar left on the bag, the mass would've stayed the same. Water + water = water therefore no major changes occurred. The 1M solution was the heaviest out of all of them because it contained the least amount of space for water (hypotonic) and it had the highest amount of sugar. Therefore the most amount of water has to go into the bag out of all of them. Osmosis is when water moves in and out the cell membrane. The water wants to equal out the concentration to reach equilibrium Osmosis is a type of passive diffusion, osmosis can be speed up by aquaporfins.

1C: Potato cores
The mass of the potato cores went down as the molarity of the solution went up. This happened because the molarity of the solutions were higher, water had to leave the potato in order to reach equilibrium. In the solution of the distilled water, the mass in fact went up because of the amount of the water in the solution. Since the solution was pure water with no sugar, the potato core was in a hypotonic solution. This means that water diffused into the potato cores, causing it's mass to go up, and it to become turgid. The solutions that were hypertonic to the potato such as 1M solution, water left the potato by osmosis. The mass went down and the became flaccid.IMG_7133.jpg

1E: Onion Cell
In this experiment  there were 3 onion cells . One onion cell was in plasmolysis . This is when the cells in hypertonic, the cell looks shrivels a. It becomes shriveled because water leaves the cell .The onion cell was  then flooded with water the cell became  turgid or hypotonic. Under the microscope the cell looked imploded.  It looked like that because for plants when they become hypotonic their cell walls push back , this is different from humans because when human cells become hypotonic they explode. Plants cells push back. The last onion cell become flaccid or isotonic. This is when the water content and the outside content are equal. The for humans this is a normal and good state to be in. For plants this is below normal levels, plants need to be in hypotonic. It is better for them to be bursting with water.IMG_2221.jpgIMG_2852.jpgIMG_0416.jpg Pink picture: Plasmolysis. Red picture: flaccid Blue picture: turgid
Conclusion- Conclusion

1A: During the 1A experiment , the results we collected showed us that glucose and iodine can pass through a selectively permeable membrane and will pass through when the concentrations are not equal.  This was shown when the color of the liquid in the bag turned from a color less to a dark blue.  The starch solution did not pass through the selectively permeable membrane into the bag because the starch molecules were too large.  We concluded this from the fact that the starch solution started out color less and after the 30 minutes of soaking remained color less.

1B: In The 1B experiment, the results showed that sucrose cannot pass through a selectively permeable membrane.  Instead the water move in and out of the membrane trying to reach equilibrium. This is done through osmosis I which is when water tries to equal out the concentration on either side of the selectively permeable membrane.

1C:  In the 1C experiment we concluded that potatoes contain sucrose molecules which make it unable to pass through a selectively permeable membrane. This was shown when the cores took in water while they were sitting in the water for 30 minutes.  We came to this conclusion when the onions weighed more after they sat in the distilled water. This means they contained less water and more solute potential than the distilled water, which is why the eater rushed in to try and reach equilibrium.

1E:  If we had done the 1E experiment, the onion cells would have plasmolyzed due to the addition of NaCl to the cells.  This shows that the onion cells had a higher water concentration that outside the cell.  This is why the water rushed out of the onion cell trying to equal out the water concentration.
References-
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/bio%20101%20lectures/cells/cells.htm
http://www.biologyjunction.com/ap_lab1_osmosis_sample_3.htm
http://encyclopedia2.thefreedictionary.com/Permeability+of+Biological+Membranes


No comments:

Post a Comment