Question

scenario 3:
you notice a plant is looking
wilted. you water it, and an hour
later the plant is standing up
straight.
q1. tonicity of the solution?
q2. how do the cells respond?
q3. what question could you ask
to confirm?

Explanation:

Q1

The plant was wilted (cells likely plasmolyzed, hypertonic environment before watering). After watering, the plant recovered. Watering adds a solution (water) with lower solute concentration than the plant cells’ interior. A hypotonic solution has lower solute concentration outside the cell, so water enters the cell. For plant cells, this causes turgor. So the water (the solution added) is hypotonic relative to the plant cell sap.

In a hypotonic solution (water has less solute than plant cells), water moves into the plant cells via osmosis (from low solute to high solute concentration, or high water potential to low water potential). Plant cells have a cell wall, so when water enters, the vacuole and cytoplasm expand, pushing against the cell wall. This causes the cells to become turgid (regain turgor pressure), which makes the plant stand upright.

To confirm the tonicity and cell response, we can test variables related to the solution or cell state. For example, asking if the plant would wilt again if we stop watering (to see if it was due to water deficit, related to hypotonic solution effect) or if adding a hypertonic solution (like salt water) would cause wilting (to test osmosis in reverse). Another question: “What happens if we add a concentrated salt solution to the plant now?” (to see if cells lose water, plasmolyze, showing they were turgid from hypotonic water).

Answer:

The solution (water) is hypotonic.

Q2