Find Osmolarity of Potato Cores | Lab Tips

[kenny87]

We did a lab in my class where we put slices of potatoe into solutions with different molar concentrations of sucrose. Now, I am asked to find the osmolarity of the potatoe cores. How do I do this?

 

[iansmith]

Can you give us the details about the observation you had. For example what happen to the potato in the no sucrose vs the highest concentration of sucrose.

What do you think the osmolarity is based on these observation?

 

[kenny87]

Potato Osmolarity...Again

Hi, after doing a diffusion/osmosis lab, I am being asked to determine the osmolarity of a the potato cores. We recorded the cores' initial mass, placed them in sucrose solutions of varying molarities, and then weighed them one day later. Here are my results:

Sucrose Solution Initial Mass (g) Final Mass (g)
1M 3.071 2.202
.8M 2.953 2.162
.6M 2.894 2.271
.4M 2.862 2.511
.2M 3.112 3.201
Distilled Water 3.021 3.783

I determined the molarity of each solution myself and calculated the percent differences, but I don't know how to "determine the osmolarity of the potato cores". My teacher said that it is up to us to figure out how to do this. I've looked up osmolarity on the internet, but all I see are equations about specific number of particles, etc. I have no idea how to do this with a potato. Please help me out! Thanks!

 

[iansmith]

try to remember what happens when a cell is in hypothonic, isotonic and hypertonic solution. Which sucrose concentration fits in the hypothonic, isotonic and hypertonic solution when compared to the potato (hint: Look a the percentage weight change between each sample. Is it negative, positive or neutral). Based on this you should have a idea where the osmolarity of the potato is.

 

[kenny87]

I know that ones with a negative percent difference will be hypertonic, and the ones with a positive difference are hypotonic; but I still don't see how to find the osmolarity... I was looking on the internet and I found a sample AP test with the exact same question potato and all, so I know this is something that has a rather specific answer, but I really have no clue as to how to find it.

 

[iansmith]

Look for osmole value for animal and plant cells.

Check this page
http://faculty.washington.edu/kepeter/119/labs/cell-lab-2005.pdf

 

[kenny87]

I'm sorry, but I'm still really confused. I didn't see any information on that page concerning potato slices and the particles that will ionize, etc. I really, really don't know what to do here. I understand the how to find osmolarity: n*moles where n is the number of particles that will disassociate. I still have no idea how to do this with a potato.

Because this is a potential AP question, it almost seems to me that this is a question that I shouldn't need a specific numbers that will not be given to me, as no formulas are given here: http://www.collegeboard.com/prod_downloads/ap/students/biology/ap05_frq_biology_b.pdf

I appreciate all of the help that I've been given thus far, but I'm still not making the connections that I need to.

 

[iansmith]

There is no formula to sove this problem. This is what you are suppose to do:

First, calculate the osmole value of your glucose solutions.
Second, you have to graph the data (osmole on x-axis and % change in mass on the y axis).
Third, make a best fit curve and find the slope.
Forth, solve for x when y=0.