CourseCourseConceptConceptDocumentDocument

IB Biology SL D2.3 Water Potential Questions

Explain osmosis, interpret plant-tissue mass data and predict plant, animal and protist cell responses in IB Biology SL D2.3.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam points

  • State osmosis requirements and infer water movement toward higher solute concentration.
  • Use isotonicity to explain no net osmosis and predict lysis or crenation in wall-less cells.
  • Explain how contractile vacuoles remove excess water from freshwater protists.
  • Predict plant-cell turgor or plasmolysis from hypotonic or hypertonic exposure.
  • Calculate percentage mass change and use the zero-change intercept to estimate tissue isotonic concentration.
  • Assess plant-tissue osmosis methods using controls, scatter, trends and outliers.
  • Choose isotonic transplant storage solutions to prevent net water movement.

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 applications

Question 1

[Maximum number: 3]

The figure represents a water molecule.

Water-molecule diagram with a circle labelled O joined by solid lines to two smaller circles labelled H, one to the right and one below.

Water has important solvent properties. Explain these properties using an example to illustrate your answer.

Question 2

[Maximum number: 2]

Question (a)

(a)

A study was done on the osmolarity of semen and sperm movement (motility).

Figure for Question (a) — IB Biology SL
[ 1 ]

Question (i)

(i)

The same study showed that blood plasma has a lower osmolarity than semen. Explain how that would affect the movement of water between blood plasma and semen.

[ 1 ]

Question (b)

(b)

Explain a change that would take place in sperm placed in a hypotonic solution.

[ 1 ]

Question 3

[Maximum number: 3]

The electron micrograph shows the surface membrane of an animal cell.

Electron micrograph of an animal cell membrane with a densely textured region X on the left and a smoother surface with scattered raised features on the right. Scale bar: 0.1 μm.

Explain the reason that animal cells and tissues under investigation must be maintained in solutions with the same osmolarity.

Question 4

[Maximum number: 1]

A study was done on the osmolarity of semen and sperm movement (motility).

Figure for Question 4 — IB Biology SL

The same study showed that blood plasma has a lower osmolarity than semen. Explain how that would affect the movement of water between blood plasma and semen.

Question 5

[Maximum number: 3]

An experiment was carried out to determine the change in mass due to osmosis. Potato cubes were soaked in different concentrations of sodium chloride for 12 hours. The table shows the mean data for the mass of potato before and after the 12-hour period.

Table for Question 5 — IB Biology SL

Question (a)

(a)

Explain how the data may be used to determine the solute concentration of the potato tissue.

[ 2 ]

Question (b)

(b)

Estimate the solute concentration of the potato tissue.

[ 1 ]

Question 6

[Maximum number: 1]

Explain a change that would take place in sperm placed in a hypotonic solution.

Question 7

[Maximum number: 7]

Water is one of the most abundant molecules on Earth. Living organisms must maintain homeostatic levels of water to survive.

Explain the process of osmosis with reference to its effects on plant cells.

Question 8

[Maximum number: 1]

A human organ is being prepared for transplant. In what type of solution must it be bathed?

A

A hypertonic solution

B

A hypotonic solution

C

Pure water containing no solutes

D

A solution with the same osmolarity as the organ tissue

All question bank results loaded