The question
Name: ______________________ Date: ____________ Plasmolysis in onion cells (4 points)
Data table
Plasmolysis in onion cells
Students peeled thin layers of epidermis from two groups of red onions: onions grown with normal watering and onions grown under drought. They placed pieces in sucrose solutions for 20 minutes and, under a microscope, counted 100 cells per piece, recording how many were plasmolyzed. Each value is the mean of four pieces.
| Sucrose concentration (mol/L) | Normally watered onions (% plasmolyzed) | Drought-grown onions (% plasmolyzed) |
|---|---|---|
| 0.0 | 0 | 0 |
| 0.2 | 2 | 0 |
| 0.3 | 18 | 3 |
| 0.4 | 51 | 16 |
| 0.5 | 83 | 48 |
| 0.6 | 97 | 80 |
| 0.8 | 100 | 99 |
(a) Describe the relationship between sucrose concentration and the percent of plasmolyzed cells in the normally watered onions. [1 point]
(b) Using the data, calculate the difference, in percentage points, between the two groups at 0.4 mol/L sucrose, and identify the sucrose concentration at which about half of the drought-grown cells are plasmolyzed. [1 point]
(c) Explain, in terms of water potential, why cells become plasmolyzed in the stronger sucrose solutions. [1 point]
(d) A student claims that drought-grown onion cells contain a higher concentration of dissolved solutes than normally watered cells. Justify the claim using the data, and explain how this difference could help a plant growing in dry soil. [1 point]