When testing tonicity in Elodea cells, once Elodea cells were placed in distilled water, what did you observe? Select all that apply.
A.
Cell membranes pressed tightly against the cell walls.
B.
Many of the cells had burst.
C.
Full central vacuoles.
D.
Many of the cells had become crenated.
The Correct Answer and Explanation is:
When Elodea cells are placed in distilled water, the correct observations are:
A. Cell membranes pressed tightly against the cell walls.
C. Full central vacuoles.
Explanation:
Elodea cells are plant cells that have a rigid cell wall and a central vacuole. Understanding their behavior in different tonic environments helps elucidate the concept of osmosis and tonicity.
1. Cell Membranes Pressed Tightly Against the Cell Walls:
Elodea cells, when placed in distilled water, experience a hypotonic environment. In a hypotonic solution, the concentration of solutes outside the cell is lower than the concentration inside the cell. This difference in solute concentration causes water to enter the cell through osmosis.
As water enters the cell, the central vacuole fills up and exerts pressure against the cell membrane. This pressure, known as turgor pressure, pushes the cell membrane against the cell wall. The cell wall provides structural support and prevents the cell from bursting under this pressure. Hence, the cell membrane presses tightly against the cell wall.
2. Full Central Vacuoles:
In a hypotonic environment, the central vacuole of the Elodea cell fills with water. This accumulation of water occurs due to the influx of water into the cell, which is trying to balance the solute concentration inside the cell with that outside. As the vacuole fills, it increases in size, contributing to the turgor pressure mentioned above.
Why the Other Options are Incorrect:
- Many of the cells had burst (B): This is incorrect because plant cells generally do not burst in a hypotonic environment due to the protective nature of the cell wall, which prevents excessive expansion.
- Many of the cells had become crenated (D): Crenation refers to the process where cells shrink and develop a scalloped edge due to water loss in a hypertonic environment. This does not occur in Elodea cells placed in distilled water, as distilled water is hypotonic, not hypertonic.
In summary, in a hypotonic solution like distilled water, Elodea cells will show cell membranes pressed tightly against the cell walls and full central vacuoles due to the osmotic movement of water into the cell.