The hypothesis was the following, if an egg is placed in water with a higher concentration of dissolved particles on the outside of the membrane the concentration gradient that is formed will cause the water to diffuse into the egg causing the membrane to expand and there fore cytolysize. Hypertonic is the process of having an osmotic pressure greater than that of the solution with which it was compared. Hypotonic refers to a solution having an osmotic pressure less than that of the solution with which it was compared. Isotonic is applied to solutions that have identical concentrations of solute molecules and hence the same osmotic pressure. Plasmolysis is the shrinkage of the cytoplasm and the pulling away of the plasma membrane from the cell wall when there is water loss. Cytolysis is the bursting of a cell. Isomolysis is the process of achieving isotonicity.
The materials used were two 250ml beakers, two eggs, 150ml of tap water for each beaker, ten grams of salt, one stirring rod, 100ml graduated cylinder, and a balance. The two 250 ml beakers were filled with 150ml of tap water by using the 100ml graduated cylinder to evenly measure out the water. In one of the beakers, ten grams of salt was put in and dissolved by using a stirring rod. Then the eggs were measured on a balance in grams and recorded. The eggs were then placed into the beakers, one with the dissolved salt, and one without salt. Then, the beakers were covered with parafilm. The mass of the eggs was taken and recorded during the next three days.
The results that were collected on the first recording show that when egg number one was placed in a solution of water and salt with 150ml of tap water and 10g of salt the egg gained 12.9g from the initial mass of 80.3g to a mass of 93.2g. The results collected during the same time period from egg number two which was placed in 150ml of tap water show that it gained 13.7g from 74g to 87.7g. The next set of data collected shows that egg number one gained an additional 2.9g from 93.2g to 96.1g. Egg number two gained 3.8g from 87.7g to 91.5g. On the last measuring session egg number one gained 0.7g from 96.1g to 96.8g. Egg number two gained 2.3g from 91.5g to 93.8g. See attached graph “Results”. As the results show egg number two gained more mass than egg number one. This was an unexpected result as it was thought that the egg immersed in the solution with dissolved salt would gain more mass.
The materials were chosen as they were because they provided adequate volume and accessibility. A 100ml beaker could have been chosen over the 250ml beaker because the eggs fit in them but there would be no room for expansion as the membrane expands. Therefore the 250ml beaker was chosen. The 100ml graduated cylinder was chosen because if any smaller graduated cylinder was used many more measurements would be required to fill up each 250ml beaker with 150ml water. A stirring rod was used to aid in the dissolving of salt in water. 150ml of water was used in each beaker because it sufficiently covered the eggs. 10g of salt was dissolved into the water of egg number one. This amount was chosen because it was enough to form a sufficient concentration gradient. The data refutes the hypothesis because egg number two without salt gained more mass than egg number one. Also egg number two gained mass more rapidly than egg number one. One possible reason for this is that the dissolved salt in the water of egg number one clogged the pores in the membrane. The data shows that both eggs gained mass at fairly equal rates, gaining the most between the initial and first reading, gaining slightly less between the next readings and topping out between the last two. Some changes and improvements that could be made in the experiment would include adding more levels of salt so that there is an array of beakers each with slightly more salt than the last and also recording results for a longer time period.
In conclusion the experiment showed that in this instance adding salt to the outside of the membrane did not cause more water to enter the egg. Not enough data was gathered to tell exactly why this occurred. The hypothesis could be changed to state that if an egg is placed in water with salt the egg will gain mass at a slower rate than an egg placed in plain tap water.
