Why do herbaceous plants wilt when they do not have enough water and stand erect when they have water?

Answer 1

This relates to the type of solution the plant cells are exposed to. In general, there are 3 distinct types of solutions in nature: hypotonic, isotonic, and hypertonic. A hypotonic solution is one that has a low concentration of a solute relative to the solute concentration inside the cell, such as distilled water. An isotonic solution has the same solute concentration as the inside of the cell. A hypertonic solution has a higher concentration of solute than the inside of the cell.

Back to the plants...
When plants wilt, that means the are exposed to an isotonic solution. When this happens, the net amount of water moving between cells and the environment is equal. As a result, the cell becomes flaccid and the plant wilts.


When plants stand erect, this is a result of turgor pressure. When in a hypotonic solution, such as distilled water, the plant cells absorb the water and store it in its central vacuole. The cell cytoplasm enlarges and pushes up against the sturdy cell walls. This cell is said to be turgid, or stable.