Q BankQuestion BankDocsDocuments

D2.3 Water potential

Water potential explains osmosis, solute effects, plant tissue changes, cell swelling, plasmolysis and isotonic medical conditions in living systems and cells.

Syllabus
First assessment 2025
Topic
D2.3
Level
HL

Exam analysis

Chance of appearing17%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–2

Most tested objectives

Common question formats

  • Definition or recall
  • Process explanation
  • Calculation
  • Data analysis
  • Diagram interpretation

Recent exam appearances

November 2025Paper2 ["HL"] · TZ19(c)[ 4 ]D2.3.7—Medical applications
November 2025Paper2 ["HL"] · TZ34(a)[ 3 ]D2.3.10 (HL)—Solute and pressure potential
November 2025Paper1A ["HL"] · TZ120[ 1 ]D2.3.10 (HL)—Solute and pressure potential
May 2025Paper1A ["HL"] · TZ320[ 1 ]D2.3.10 (HL)—Solute and pressure potential
November 2024Paper3 ["HL"] · TZ02(c)[ 1 ]D2.3.5—Effects on cells without wall
Practice this topic

Coverage 2016–2025 · Updated 16 Jul 2026

Objective notes

11 learning objectives
D2.3.1Solvation with water

• Water forms hydration shells around ions and polar solutes

• Hydrogen bonding and charge attraction reduce free water movement

D2.3.2Water movement

• Water moves by osmosis across partially permeable membranes

• It moves from hypotonic/lower solute solutions toward hypertonic/higher solute solutions

D2.3.3Osmosis into/out of cells

• Osmosis direction depends on internal and external solute concentration

• Isotonic conditions have dynamic water movement but no net osmosis

D2.3.4Changes in plant tissue

• Plant tissue changes mass or length when placed in sucrose solutions

• Percentage change graphs estimate isotonic/osmotic concentration

D2.3.5Effects on cells without wall

• Animal cells can lyse in hypotonic solutions and crenate in hypertonic solutions

• Freshwater protists use contractile vacuoles to expel excess water

D2.3.6Effects on cells with wall

• Plant cells become turgid in hypotonic solutions as vacuoles swell

• Hypertonic solutions cause flaccidity and plasmolysis from water loss

D2.3.7Medical applications

• Isotonic saline prevents harmful water gain or loss in body cells

• IV fluids and transplant organ baths must match tissue osmotic concentration

D2.3.8(HL)—Water potential

• Water potential is potential energy of water per unit volume, measured in kPa

• Pure water at standard conditions has water potential of 0 kPa

D2.3.9(HL)—Movement from higher to lower potential

• Water moves from higher water potential to lower water potential

• Solutes lower water potential by restricting water molecule movement

D2.3.10(HL)—Solute and pressure potential

• Water potential equals solute potential plus pressure potential

• Solute potential is zero or negative; pressure potential is often positive in walled cells

D2.3.11(HL)—Water potential in plant tissue

• Water entering plant cells increases pressure potential and dilutes solutes

• Water leaving plant cells lowers pressure potential and makes solute potential more negative

ConceptIB Biology HL