explain why plants appear wilted when the surrounding solution is isotonic?

Answer 1

Plants must have water pressure inside the cells in order for the cell walls to be adequately supported with pressure from inside. An isotonic solution allows water to move equally into and out of the plant cells. In order for the plant not to be wilted, the solution should be slightly hypotonic.

Answer 2

The answer is found in the quote "Water water everywhere but nary a drop to drink."

Humans and plants have a chemical reaction that gets water both in and out of individual cells. For humans isotonic water is salt water.

As for plants, water has to get from a plant's capillaries or any internal or external distribution system into the cell. To do this they are like us humans, use a chemical reaction.

Humans can't drink salt water because salt water is isotonic, without going into too much detail, we need salt water inside our cells which is why we do need some salt in our diets and phosphorous. Phosphorous is found in most of our food, both animal and vegetable.

In the human salt/phosphorous water cycle salt water moves from inside the cell and fresh water moves to inside a cell because of the chemical reaction between salt and phosphorous.

So isotonic water for humans would be salt water or more properly water that has a salt ion chemically bound to it. For plants isotonic (which comes from the word ion) the water contains an ion in it which makes it impossible for cellular exchange of water to occur.

So the plant is wilted because it can't use the water in it's environment.

Answer 3

The root cells cannot get enough mineral ions from the soil by diffusion alone. The inside of the cell must be hypertonic to the environment. The soils solution is too dilute. Active transport of these ions must occur. Specific carrier proteins in the plasma membrane attract and carry their specific mineral into the cell. A Proton Pump: H+ is pumped out of the cell causing a change in pH and a voltage across the membrane. This helps drive the anions and cations into the cell. .

Water transported up from the roots must replace water lost by transpiration. Xylem sap rises against gravity, driven by a gradient of water potential. Water flows from an area of high potential to an area of low potential. Water Potential is expressed in units of pressure: 1 bar is the pressure needed to push up a column of water 10 meters. 1 megapascal = 10 bars. Pure water has a potential of 0. Addition of pressure increases water potential. Addition of solutes decreases it.
When transpiration is low, ions pumped into the stele decrease water potential and cause water uptake by the stele. This uptake force is called root pressure. It Cannot keep pace with transpiration, and can only force water up a few meters.

Answer 4

Your plant does not have the proper drainage. Your plant may need to be re-potted to a larger pot and/or the potting soil in the pot needs to be loosen up. Also use a search engine to search for "poor drainage problems in plants" for further information.