Transpiration and Translocation Flashcards
What is transpiration?
Loss of water vapour by evaporation through stomata
Function of transpiration:
Cool plant down
Causes transpiration stream
~~> delivers H2O + mineral ions
Describe the process of transpiration?
Water evaporates out of stomata.
Diffuses out leaf into air
Higher WP to lower WP
As water leaves leaf, it creates tension that pulls more water into leaf (transpiration pull)
~~~> cohesion-tension theory
Capillary action : water moving against gravity
Due to adhesion + cohesion
Evidence for cohesion-tension theory:
Changes in the diameter of trees.
When a xylem vessel is broken
How does the stomata control rate of transpiration?
When turgor is low the asymmetric configuration of the guard cell walls closes the pore.
When the environmental conditions are favourable guard cells pump in solutes by AT, increasing their turgor (rigidity).
Cellulose hoops prevent the cells from swelling in width, so they extend lengthways.
Inner wall = less flexible than the outer wall,
~~>cells = bean-shaped and open the pore.
What are the factors that increase rate of transpiration?
Higher temperature
Lower humidity
Higher air movement
Higher light intensity
Soil-water availability
What does a potometer do?
Measures water uptake by plants
Estimates transpiration rate
The water can be used in:
Photosynthesis
Maintaining turgor pressure
Calculation?
Measure distance travelled by air bubble
Calculate volume of H2O
uptake
^r2 x d (cylinder)
What is translocation?
Transport of assimilates (products of photosynthesis) from source to sink in plants.
Describe phloem loading in the apoplast pathway:
Require energy
—> released in form of ATP by respiration in mitochondria.
H+ ions pumped out companion cell through H+ pumps by AT
H+ conc higher outside companion cell
H+ = diffuse back to CC
—> co-transported with sucrose into CC via co-transporters
What happens to the sucrose in the CC?
Sucrose diffuses from CC into sieve tube element through plasmodesmata
—>lower water potential in STE
H2O moves into STE by osmosis
—> generates turgor pressure (pressure exerted by fluid that presses cell membrane against cell wall)
for mass flow.
What is mass flow?
Assimilates moving from the source (high pressure) to the sinks (low pressure) down pressure gradient.
