Content Objective: Explore water potential as a key concept in understanding water movement in plants, focusing on its measurement relative to pure water and the roles of solute and pressure potentials. Examine how water potential influences water movement from higher to lower potential areas and its impact on plant tissues in various solutions.
Language Objective: Discuss the principles of water potential, including solute and pressure contributions, using appropriate scientific terminology and the equation ψw = ψs + ψp. Explain the effects of hypotonic and hypertonic solutions on plant tissue, employing concepts of water potential to analyze changes.
Syllabus Details:
D2.3.8 (HL) —Water potential as the potential energy of water per unit volume - "Students should understand that it is impossible to measure the absolute quantity of the potential energy of water, so values relative to pure water at atmospheric pressure and 20°C are used. The units are usually kilopascals (kPa)."
D2.3.9 (HL) —Movement of water from higher to lower water potential Students should appreciate the reasons for this movement in terms of potential energy.
D2.3.10 (HL) —Contributions of solute potential and pressure potential to the water potential of cells with walls - "Use the equation ψw = ψs = ψ p. Students should appreciate that solute potentials can range from zero downwards and that pressure potentials are generally positive inside cells, although negative pressure potentials occur in xylem vessels where sap is being transported under tension."
D2.3.11 (HL) —Water potential and water movements in plant tissue - "Students should be able to explain in terms of solute and pressure potentials the changes that occur when plant tissue is bathed in either a hypotonic or hypertonic solution."
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