When Elodea leaves were placed in 10% NaCl, what was the result?
a. The cell membrane shrank away from the cell wall because the solution was hypertonic.
b. The cell membrane shrank, but the central vacuole remained full.
c. The cells burst because the solution was hypotonic.
d. The cell became turgid.
The correct answer and explanation is :
The correct answer is a. The cell membrane shrank away from the cell wall because the solution was hypertonic.
Explanation:
When Elodea leaves (a freshwater plant) are placed in a 10% NaCl (salt) solution, the surrounding solution becomes hypertonic relative to the interior of the plant cells. This means that the concentration of solutes (in this case, salt) outside the cell is higher than inside the cell. In a hypertonic solution, water molecules tend to move from areas of lower solute concentration (inside the cell) to areas of higher solute concentration (the outside solution). This process is called osmosis.
As water leaves the plant cell through osmosis, the volume of the central vacuole decreases, and the cytoplasm shrinks. This causes the cell membrane to pull away from the rigid cell wall. The cell wall remains intact and does not shrink because it provides structural support. However, the shrinkage of the cell membrane is noticeable and is called plasmolysis, which is a characteristic response to hypertonic conditions in plant cells.
Here’s why the other options are incorrect:
- b. The cell membrane shrank, but the central vacuole remained full: This would not happen in a hypertonic solution because the water from the vacuole would exit the cell to balance the concentration difference, causing the vacuole to lose water and shrink.
- c. The cells burst because the solution was hypotonic: This is incorrect because a hypotonic solution (lower solute concentration than inside the cell) would cause water to enter the cell, leading to swelling or potential bursting. A hypertonic solution, on the other hand, causes water to leave the cell.
- d. The cell became turgid: This is a characteristic response to a hypotonic solution, where the plant cell fills with water, and the cell wall prevents bursting. In a hypertonic solution, the opposite occurs, and the cell loses water, not gaining it.
In conclusion, when Elodea leaves are placed in a 10% NaCl solution, the cells undergo plasmolysis, and the cell membrane shrinks away from the cell wall due to the hypertonic nature of the solution.