Osmosis：練習題

What term describes the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane?

A student investigates osmosis by placing a dialysis tubing bag containing a 15% sucrose solution into a beaker of distilled water. Which statement describes the initial movement of molecules across the membrane?

The table below shows the results of an experiment where identical potato cylinders were immersed in various concentrations of sucrose solution for 24 hours. The initial mass of each cylinder was \( 5.00 \text{ g} \).

\( \begin{array}{|c|c|} \hline \text{Concentration (mol/dm}^3) & \text{Final Mass (g)} \\ \hline 0.0 & 5.85 \\ \hline 0.2 & 5.30 \\ \hline 0.4 & 4.75 \\ \hline 0.6 & 4.20 \\ \hline \end{array} \)

Based on this data, what is the approximate concentration of the sucrose solution that is isotonic to the potato cells?

Water moves into and out of cells via which specific process, through the partially permeable cell membrane?

A plant is growing in a field where the soil is well-watered. Which condition within the root hair cells allows the plant to maintain turgor pressure for support?

Through what type of membrane does water diffuse during osmosis?

Explain how the turgor pressure within a plant cell contributes to the overall support of a non-woody plant structure.

In an experiment, an identical potato strip is placed in an unknown solution. After several hours, the strip becomes flaccid. Deduce the relative water potential of the unknown solution compared to the potato cells and explain the underlying osmotic movement.

(a) Define osmosis as the net movement of water molecules.
(b) Describe the effects of immersing a plant cell in a dilute solution and a concentrated solution, using the terms turgid, flaccid, and plasmolysis.
(c) Explain the importance of osmosis in the uptake of water by plant root hair cells.

The bacterium Vibrio cholerae causes severe dehydration through a mechanism involving the movement of ions and water in the small intestine.

(a) Explain how the toxin produced by the bacteria causes chloride ions to move into the lumen of the small intestine, and identify the specific transport process involved.
(b) Describe the effect this accumulation of chloride ions has on the water potential of the intestinal lumen.
(c) Use the principles of osmosis to explain why this leads to the symptom of watery diarrhea and extreme dehydration.