Use osmotic water movement and cell-wall mechanics to explain turgor pressure, plasmolysis and prevention of bursting in IB Biology HL D2.3.6.
Plants have cell walls composed of cellulose.
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 .
Outline how pressures higher than atmospheric pressure develop inside plant cells.
a. entry of water by osmosis;
b. because solute concentration is higher inside (the cell) / because solute/water potential is more negative inside / because the bathing medium is hypotonic;
c. because cell wall does not expand / cell wall prevents the cell from increasing in volume / cell wall allows high pressure/turgor pressure to build up (without the cell bursting);
Marking guidance:
Reject statements that the cell wall
can prevent water leaving the cell.
2
max
State the importance of cellulose to the plant when the pressure is higher inside the cell than outside.
prevents bursting;
Marking guidance:
Do not accept 'prevents collapsing'