Final answer:
The phenomenon observed when Elodea cells are placed in a hypertonic solution, leading to the loss of water and the plasma membrane detaching from the cell wall, is known as plasmolysis.
Step-by-step explanation:
When Elodea cells are placed in a hypertonic solution, the phenomenon observed is called plasmolysis. This describes the process where the cell loses water and the plasma membrane detaches from the cell wall, resulting in the constriction of the cell membrane.
Unlike animal cells, plant cells have a rigid cell wall that prevents them from bursting in a hypotonic environment, but in a hypertonic environment, the fluid movement is out of the cell causing it to become flaccid as it loses turgor pressure. Plasmolysis can be observed in plant cells that have been underwatered and become wilted due to the absence of adequate turgor pressure to keep the cells turgid and the plant upright.