Cell Membranes and Transport

Topics: Osmosis, Diffusion, Temperature Pages: 5 (1354 words) Published: July 21, 2013
Cell Membranes and Transport
Hands-On Labs, Inc. Version 42-0033-00-01

Exercise 1: Diffusion

Data Table 1: Rate of diffusion in different temperatures| | ºC| Minutes|
Temperature| InitialTemp.| InitialColor| 5| 10| 15| 20| 25| 30| 60| Cold| 10°celsius| clear| clear| clear| clear| clear| clear| light purple| light purple| Ambient| 25°celsius| clear| clear| clear| clear| light purple| light purple| med purple| med purple| Hot| 75°celsius| clear| purple| purple| purple| purple| dark purple| dark purple| dark purple|


A. Write a one-paragraph analysis of the results for the procedure. Provide reasons for the difference in the rate of diffusion at the different temperatures.

- In this experiment three zip-loc bags were filled with a solution of starch. Each bag was placed in different beakers filled with IKI indicator and placed at different temperatures. When Iodine reacts with starch, it turns purple. The rate that a solution diffuses along a grain or membrane Is related to the concentration, the type of membrane and the temperature. Because the concentration of the solutions and type of membrane is the same, the only factor to determine the rate of diffusion in this experiment is the temperature. When molecules are placed in a hot temperature they become excited; And the higher the temperature the higher the rate of diffusion.That is why in this experiment, the zip-loc placed in the hot water bath achieved the fastest rate of diffusion when compared to the solutions placed in the refrigerator and in ambient room air.

B. Did the sizes of the molecules affect their movement?

-Yes sizes of molecules affect their movement during diffusion. In this experiment, the size of the iodine molecules were small enough to pass through the semi-permeable membrane causing the reaction with color change. On the contrary, the starch molecules were too large to pass through the membrane. This is tested by the fact that the surrounding solution in the beaker was not contaminated or cause a reaction, only that in the zip-loc.

C. Give an example of diffusion between: a solid and a liquid; a gas and a liquid; between two different solids.

- I have a perfect example of diffusion between a solid and a liquid. I have a paper cup that was left in the cup holder of my car for a couple of days, and when I finally decided to throw this cup away, I realized that the liquid soaked through the cup and spilled into the cup holder. The reason that this is diffusion is because the cup was left in a hot car and this not only made the diffusion rate increase but it also eventually weakened it. An example of a gas and a liquid is liquid nitrogen being poured into a cryogenic tank. Liquid nitrogen stats off as a gas and when placed into a container, it eventually fills the container while becoming a liquid in the process. An example of diffusion between two solids includes sand and marbles, when both placed into a container each will fill the container without changing forms or reacting within one another. If the membranes are permeable enough to allow diffusion than it will move from the higher concentration to a lower, if not it will just stay the same in both forms.

Exercise 2: Osmosis

DataTable 2: Potato Mass|
| Initial Mass of Two Potato Strips| Final Mass of Two Strips| MassDifference| % Change inMass| Class Average Percent Change in Mass (if available)| a) Distilled Water| 1.2g| 1.2g| 0g| 0%| n/a|

b) 1.0 M Sucrose| 1.1g| 1.0g| 0.1g| -10%| n/a|
c) 0.8 M Sucrose| 0.9g| 0.7g| 0.2g| -22%| n/a|
d) 0.6 M Sucrose| 0.9| 0.7g| 0.2g| -22%| n/a|
e) 0.4 M Sucrose| 0.9g| 0.8g| 0.1g| -11%| n/a|
f) 0.2 M Sucrose| 0.9g| 0.9g| 0g| 0%| n/a|

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