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.

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 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 D2.3.8 (HL)—Water potential D2.3.9 (HL)—Movement from higher to lower potential D2.3.10 (HL)—Solute and pressure potential D2.3.11 (HL)—Water potential in plant tissue

[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.

[Maximum number: 1]

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

Decreases movement of water from soil into the root

Absorption of water with a higher solute concentration

Increases movement of water from soil into the root

Absorption of water with a lower solute concentration

[Maximum number: 1]

What would result from drinking large quantities of water?

[Maximum number: 3]

Data was collected on rabbit red blood cells that were exposed to sodium chloride (NaCl) and scorpion venom. Under some osmotic conditions red blood cells swell and burst, releasing hemoglobin (hemolysis). The graph shows the response of red blood cells to different concentrations of sodium chloride, with and without scorpion venom.

Describe how the variables would be controlled in an experiment to estimate the osmolarity of plant tissue.

[Maximum number: 2]

Outline the effect of the venom on the hemolysis of red blood cells.

[Maximum number: 3]

Plants have cell walls composed of cellulose.

(a)

Hydrostatic pressure was measured in onion (Allium cepa) epidermis cells bathed in pure water. The mean pressure inside the cells was 250 kPa . Atmospheric pressure is usually close to 100 kPa .

[ 3 ]

(i)

Outline how pressures higher than atmospheric pressure develop inside plant cells.

[ 2 ]

(ii)

State the importance of cellulose to the plant when the pressure is higher inside the cell than outside.

[ 1 ]

[Maximum number: 4]

Living organisms have mechanisms for preventing or reducing change.

Explain the need for isotonic conditions in human blood plasma and tissue fluid.

[Maximum number: 1]

The water potential of a plant cell is -0.24 kPa . If the pressure potential of the cell is 0.46 kPa , what is the solute potential of that cell?

\Psi_{\mathrm{w}}=\Psi_{\mathrm{s}}+\Psi_{\mathrm{p}}

0.22 kPa

-0.22 kPa

0.70 kPa

-0.70 kPa

[Maximum number: 3]

(a) Explain how the pressure potential and solute potential change inside a plant root cell when it is placed into a solution that is more hypotonic than the cell's cytoplasm.

Explain how the pressure potential and solute potential change inside a plant root cell when it is placed into a solution that is more hypotonic than the cell's cytoplasm.

a. (when cell is placed in a hypotonic solution) surrounding/outside (of the root hair cell) is more dilute / has higher water potential

OR

water will enter the root hair cell

OR

water moves from high water potential to low water potential;

b. (positive) pressure potential will increase / become more positive;

c. (negative) solute/osmotic potential will increase / become less negative;

d. water potential inside the cell will increase / become less negative;

e. $\Psi_{w}=\Psi_{s}+\Psi_{p}$ ;

f. when cell's water potential equals that of the solution, (net) water movement stops;

For e. allow word equation:

$\Psi_{w}=$ water potential

$\Psi_{s}=$ solute potential

$\Psi_{p}=$ pressure potential

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question (a)

Question (i)

Question (ii)

Question 7

Question 8

Question 9