In my Bio 1 lab class we did what I am assuming is a fairly standard Bio 1 lab o

Question

In my Bio 1 lab class we did what I am assuming is a fairly standard Bio 1 lab on osmosis. We placed core pieces of potatoes into different concentrations of sucrose and measured the weight change to determine the molarity of the potato. I graphed our data and found that the potato was isotonic around .3M sucrose. I understood all of this but now I am confused about calculating osmolarity of the potato. Since sucrose does not dissociate into multiple particles (like NaCl would), is the osmolarity the same as the molarity in this circumstance or am I missing something here?

The other question was about further experiments, asking "What will determine net water movement (change in potato weight) in potato tubers, relative molarity, or osmolarity, of the surrounding solution?"

Explanation / Answer

molarity is the number of moles that are dissolved in 1L of solution and in the case of osmolarity, it is the molarity multiplied by the number of particles that are produced in the solution. Consider H2O(which obviously wouldn't break up in a solution) but lets assume you broke it into particle you would get 2 particles of H and 1 particle of O, which gives you 3 particles all together. You take the molarity that you get from H2O and multiply it by 3. By doing this you will get the osmolarity of H2O. To get osmolarity you use the formula: Osmolarity=M( molarity) x i(particles).

In the experiment which you performed in Biolab, you place the potato in the different concentrations of sucrose solution and measure the weight change to calculate molarity. after plotting your data to make a graph, it is possible to set up linear function, where you get an equation in the form of y= mx+c

using this function, it is possible to calculate the value of the sucrose at 0% change in weight - this value is equal to the osmolarity of the potato.

In order to determine net water movement in potato tubers, we need to determine the natural potato sucrose molarity. If the solution contains a higher molarity than the potato does, water will move out of the potato into the solution and this will cause potato to lose water, hence losing weight.
If the sucrose molarity of the solution is lower than the potato sucrose molarity, then water will move into the potato, hence it will increase weight.

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