--- title: "Water Potential and Osmosis Quantified" description: "Water potential puts a number on the tendency of water to move, made from solute potential and pressure potential. Cells are then predicted to gain or lose water from the numbers alone." canonical: https://lightmysky.com/learn/science/water-potential-and-osmosis-quantified-mt_dFBz-cE6W0 source: https://lightmysky.com/learn/science/water-potential-and-osmosis-quantified-mt_dFBz-cE6W0.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Water Potential and Osmosis Quantified Water potential puts a number on the tendency of water to move, made from solute potential and pressure potential. Cells are then predicted to gain or lose water from the numbers alone. Subject: Science · Area: Organisms & Life Processes · Ages 17 to 18 Page: https://lightmysky.com/learn/science/water-potential-and-osmosis-quantified-mt_dFBz-cE6W0 ## Ready when they can - Adds solute potential and pressure potential to get the water potential of a cell. - Predicts the direction of net water movement between two solutions from their water potentials. - Explains why pure water sits at zero and every solution sits below it. ## Lesson: Predict which way water will move Water potential is a single number for how much water wants to move. It is built by adding pieces: solute potential, which dissolved stuff drags down, and pressure potential, which squeezing raises and pulling lowers, plus smaller effects from gravity and clinging to surfaces. Pure water with nothing dissolved and no pressure sits at exactly zero, the reference everything is measured against. Water always moves from higher potential to lower potential. **Example.** Take a plant with pressure potential 0.21 and solute potential minus 3.50. Add the two numbers to get its total water potential: minus 3.29. Right after rain the wet soil sits near zero, which is higher, so water flows from soil into plant. After months of drought the dry soil drops below the plant, the flow reverses into the soil, and the leaf pores called stomata close to cut evaporation loss. A U-shaped tube shows the same adding logic. Push the left side with pressure and its water potential rises, so water is pushed right and the right level climbs. Now add solute to the left instead: the solute potential there falls and drags the total back down. Add just enough to cancel the pressure boost and both sides match, so movement stops. Raise the total with pressure, lower it with solute; the total decides. **Tip.** Use the number, not molecule pictures, to predict osmosis. When two solutions sit across a membrane only water can cross, water moves toward the side with more dissolved solute. What matters is the count of dissolved particles, not their size: more particles means lower water potential on that side. So compare the two totals and point the arrow from higher to lower every time. **Recap.** Add solute and pressure potentials, then move water from higher to lower. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Fluid Mosaic Model of the Cell Membrane](https://lightmysky.com/learn/science/the-fluid-mosaic-model-of-the-cell-membrane-mt_-xnAIG5hFc) - [Osmosis in Plant and Animal Cells](https://lightmysky.com/learn/science/osmosis-in-plant-and-animal-cells-mt_XciCLO69xG) ## Opens up - [Tissue Fluid and Its Return to the Circulation](https://lightmysky.com/learn/science/tissue-fluid-and-its-return-to-the-circulation-mt_0jw7uXpK3C) - [Cohesion-Tension and Water Movement in the Xylem](https://lightmysky.com/learn/science/cohesion-tension-and-water-movement-in-the-xylem-mt_9_TORolYIl)