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.

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 water D2.3.2—Water movement D2.3.3—Osmosis into/out of cells D2.3.4—Changes in plant tissue D2.3.5—Effects on cells without wall D2.3.6—Effects on cells with wall D2.3.7—Medical applications

[Maximum number: 3]

The figure represents a water molecule.

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

[Maximum number: 2]

(a)

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

[ 1 ]

(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 ]

(b)

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

[ 1 ]

[Maximum number: 3]

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

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

All question bank results loaded

a	water molecule is polar OR water has «weak» positive and negative charges
b	substances that dissolve in water are hydrophilic
c	water forms hydrogen bonds with polar substances
d	positive/hydrogen side/pole of water attracted to negative ions OR negative/oxygen side/pole attracted to positive ions
e	glucose/other example dissolves because it is polar OR sodium chloride/other example dissolves because ions are attracted to water

a	to prevent osmosis;
b	cells placed in the incorrect osmolarity might swell/burst/shrink;
c	hypotonic solution would cause water to enter cells/tissues;
d	hypertonic solutions would cause water to leave cells/tissues;
e	water loss would hinder (metabolic) reactions in cell cytoplasm OR distort appearance of the cells (for the investigation);

Covered syllabus points

Question 1

Question 2

Question (a)

Question (i)

Question (b)

Question 3