Two major forces help in the transport of water in a plant. Force A is the driving force in the movement of water during the day, whereas force B helps the movement of water in a plant during the night or during the day when humidity is very high.
(a) Identify force A and force B.
(b) Describe how each of these forces helps in the movement of water in a plant.
(a) Force A: transpirational pull
Force B: root pressure
- Root pressure is a force or the osmotic pressure generated in the roots .
- It drives the fluids and other ions from the soil in upwards directions into the plant’s vascular tissue .
- Evaporation of water from leaves of a plant is called transpiration.
- Reduced pressure at the top of the xylem vessels creates a suction which pulls up water through the xylem.
- Thus transpiration cannot occur at night/on a humid day when rate of evaporation is low.