Osmosis lab: potato cores
Question
At what sucrose concentration does a potato core neither gain nor lose mass?
Method
Six 3 cm cores, blotted and massed, then left 24 hours in 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 M sucrose. Re-massed and converted to percent change.
| Sucrose (M) | Mass change |
|---|---|
| 0.0 | +18.4% |
| 0.2 | +7.1% |
| 0.4 | −1.9% |
| 0.6 | −9.6% |
| 0.8 | −15.2% |
What the numbers say
The line crosses zero near 0.35 M, so that is the point where the sucrose solution and the potato cytoplasm sit at the same water potential. Below it the tissue is hypertonic and takes water in; above it the solution is hypertonic and pulls water out.
To do
- Plot percent change against molarity
- Read the x-intercept off the trend line
- Convert the isotonic point into a water potential in bars
- Write the error paragraph on blotting technique