Experiment: Cell Membranes and Homeostasis
Objective(s): The reason for this experiment is to see how starch and iodine affect each other and how a plastic bag works similar to a membrane in certain situations. Introduction: I know prior to doing this experiment that iodine mixed with starch creates a dark color and that most objects, organic and inorganic, naturally experience isotonic reactions. Hypothesis: I think that the potato will absorb more starch than the sweet potato and they will both absorb relatively similar amounts of water.
Procedure: Variables: Controlled- water and size of potatoes. Manipulated variables- potatoes growth based on contents of solution. Data:
- Data and Observations
- Bag ContentInitial color of water/iodine solution in the cup
- Final color of the solution in the cup Starch and Water
- Dark blue, purple Blackish Blue
- Water Orangey Orange
- Analysis Questions
Part 1
1.Restate your hypothesis and discuss if the observed results supported the hypothesis.
-Based off what I observed, my hypothesis, stating that the potato will absorb more starch than the sweet potato, was correct.
2.Identify the control and variables in your experiment.
-Variables: Controlled- water and size of potatoes. Manipulated variables- potatoes growth based on contents of solution.
3.Why do we observe the color of the solution before adding the sandwich bags to each cup?
-To make sure that the solutions contain the necessary contents.
4.Based on your observations, is the sandwich bag permeable to starch? To iodine?
-Iodine is permeable to the sandwich bag, while starch is not.
5.Look up the molecular structures of starch and iodine, and use those structures to explain your observations.
-Starch is a more complex compound than iodine, making it easier for iodine to pass through objects.
6.If a balance was available, describe how you could use it in this experiment and what the purpose would be.
-The balance could be used to also see the difference is the potatoes before and after the observation time.
7.Living organisms are made of cells. Those cells must receive nutrients and gases in order to undergo the metabolic processes that maintain homeostasis. In paragraph form, explain how you think the nutrients and gases enter the cell. Distinguish between the molecules that can enter by diffusion by simply moving across the membrane and those that must expend energy to cross the cell membrane.
-Nutrients enter cells in to major ways, through active and passive transport. When a molecule uses diffusion or other processes that require no energy, they are using passive transport. An example molecule for this would be water or glucose. Other molecules, that need to use energy to enter a cell use active transport. Many molecules that use this are macromolecules, like proteins. Molecules use one of these two transports to enter a cell.
8.List three criteria cells use to select materials to enter or leave the cell. Then explain the role of each criterion in determining the type of transport a cell will use for different sized molecules. For instance, small molecules move across the membrane by diffusion, given they are moving with the concentration gradient.
-Water can enter the cell in order to balance the amount inside to the amount of the environment. This is passive due to the fact that it happens without any external energy. -Some molecules can pass into the cell by facilitated diffusion. This is passive due to the nature of diffusion and because the solute is moving down its concentration gradient.
– Sodium is moved out of an animal cell while potassium is moved into the cell by the sodium-potassium-pump. This is through active transport because it uses energy.
9. Restate your hypothesis and discuss if the observed results supported the hypothesis.
-Based off what I observed, my hypothesis, stating that the potato will absorb more starch than the sweet potato, was correct.
10.Use your observations to explain if each type of cell (potato, sweet potato/pear/apple) was isotonic, hypertonic, or hypotonic to each of the solutions. Explain what happened to each type of cell in response to the type of solution it was in.
-Potato- it was hypertonic and gained water in the water solution. In the starch solution, it was hypotonic.
-Sweet Potato- it was hypertonic in the water solution and went through plasmolysis in the starch solution.
11.Based on the observed volume changes, which of the vegetables/fruits used in this experiment has a greater amount of sucrose in its cells? Explain your answer.
-The Sweet Potato seemed to have an originally larger amount of sucrose in its cells.
Conclusion
In conclusion, it seems like the hypothesis was relatively correct.
From the data collected from the experiment, the two potato samples were subjected to different solutions. The potato was hypertonic to the distilled water and hypotonic to the starch solution. The sweet potato, on the other hand, was a little harder to determine, though it was obvious that it was hypertonic to the distilled water, it was hard to determine if it was hypo-,hyper-, or isotonic. Since it was hard, I did a little research and realized that what I was seeing was the sweet potato going through plasmolysis. This experiment was somewhat difficult due to the fact that I was observing periodically, but it seems like it was a success.
