Osmotic Pressure: Study Notes

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Osmotic Pressure/Potential

Water Potential (ΨW)

• Water molecules possess kinetic energy, and a higher concentration of water results in higher kinetic energy, or water potential.
• Pure water has the highest water potential, set at zero at standard temperature and pressure.
• Water moves from regions of higher water potential to lower water potential.
• Water potential is measured in pascals (Ψ).

Solute Potential (ΨS)

• Solute potential refers to the reduction of water potential due to the presence of dissolved solutes.
• Solute potential is always negative; the presence of more solute decreases ΨS further.

Relationship (ΨW = ΨS)

• At atmospheric pressure, water potential (ΨW) equals solute potential (ΨS).

Osmotic Pressure

• Osmotic pressure is the negative of osmotic potential.

Pressure Potential (ΨP)

• Pressure potential increases when water enters plant cells, causing them to become turgid.
• It is usually positive but may be negative in the xylem, where it plays a crucial role in water transport.

Water Potential Equation

• Water potential (ΨW) is affected by both solute potential (ΨS) and pressure potential (ΨP).
• It is expressed as: ΨW = ΨS + ΨP.

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