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IB Biology HL D2.3 Water Potential Questions

Calculate water potential, interpret plant-tissue osmosis data and explain plant and animal cell responses in IB Biology HL D2.3.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Define osmolarity; apply osmosis to root uptake and reduced water movement in saline soil.
  • Plan fair plant-tissue osmosis tests using controlled variables and percentage mass change.
  • Plot percentage mass change against solution concentration and read the zero-change intercept.
  • Interpret plant-tissue graphs relative to the isotonic point to identify or count solutions causing mass loss.
  • Interpret hypotonic and hypertonic effects from red-cell swelling, haemolysis or crenation data.
  • Explain how contractile vacuoles remove excess water from freshwater protists.
  • Explain how water entry builds turgor and cellulose walls support plant cells.
  • Explain how isotonic plasma prevents net osmosis and mismatched fluids damage cells.
  • Use Ψw = Ψs + Ψp to calculate unknown potentials with correct signs and kPa units.
  • Infer plant-cell water and pressure-potential changes from movement between solutions.
  • Predict how hypotonic solutions alter root-cell pressure and solute potentials.

Covered syllabus points

D2.3.1—Solvation with waterD2.3.2—Water movementD2.3.3—Osmosis into/out of cellsD2.3.4—Changes in plant tissueD2.3.5—Effects on cells without wallD2.3.6—Effects on cells with wallD2.3.7—Medical applicationsD2.3.8 (HL)—Water potentialD2.3.9 (HL)—Movement from higher to lower potentialD2.3.10 (HL)—Solute and pressure potentialD2.3.11 (HL)—Water potential in plant tissue

Question 1

[Maximum number: 7]

Hydrogen bonds can exist both within and between molecules in living organisms and have an impact on their structure and function. Explain the importance of hydrogen bonding for living organisms.

Question 2

[Maximum number: 1]

Excessive irrigation can cause increased salinity in the soil. What effect does this have on water transport in the plant roots?

A

Decreases movement of water from soil into the root

B

Absorption of water with a higher solute concentration

C

Increases movement of water from soil into the root

D

Absorption of water with a lower solute concentration

Question 3

[Maximum number: 1]

What would result from drinking large quantities of water?

Table for Question 3 — IB Biology HL
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