Water potential, represented by Ψ, describes the potential energy of water relative to pure water under standard conditions. It is expressed in megapascals (MPa), a unit of pressure. By definition, pure water at atmospheric pressure has a water potential of zero.
Water potential is useful because it predicts the direction water will move between systems, such as soil, roots, stems, leaves, and the atmosphere. Water moves from a region of higher water potential to a region of lower water potential. It continues moving until the difference, ΔΨ, is reduced toward zero.
All flashcards
What is water potential?
Water potential (Ψ) is the potential energy of water relative to pure water. It predicts the direction water moves between systems and is expressed in megapascals.
What is the total water-potential equation?
Ψtotal=Ψs+Ψp+Ψg+Ψm: total water potential is the sum of solute, pressure, gravity, and matric potentials.
How do solutes affect water potential?
Dissolved solutes lower solute potential, making it more negative and thereby lowering total water potential.
What is turgor pressure?
Turgor pressure is positive pressure inside a plant cell pushing against its cell wall. It helps keep tissues firm.
What is matric potential?
Matric potential is the reduction in water potential caused by water adhering to hydrophilic surfaces, such as cell walls. It is especially significant in dry tissues and soils.
Quiz questions
What generates the tension that pulls water upward through xylem?Answer: Evaporation of water from moist mesophyll cell walls into leaf air spaces.
What substances are transported from roots toward stems and leaves by xylem?Answer: Water and dissolved mineral nutrients.
How do guard cells regulate a stoma?Answer: They change shape to open or close the pore.
What determines the direction of phloem transport in a particular tube?Answer: The locations of the sugar source and the sink that uses or stores it.
How is sucrose often loaded into phloem sieve-tube elements?Answer: A proton gradient drives uptake through a sucrose–H⁺ symporter, using metabolic energy.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.