Transpiration

The loss of water vapor from leaves

Advantages

creates transpiration pull at the top of xylem vessel;
stomata needs to be open to allow gas exchange

Disadvantage

losing water as a reactant of photosynthesis

[!def] transpiration pull
A force produced by the loss of water vapor from a leaf because of the pressure difference between roots and leaves

Wilting

[!def] Wilting
occurs then rate of transpiration > rate of water uptake

Plant lose more water than gain
not turgid, flaccid

Transpiration pull

1.  Water molecules are cohesion and adhesion -> forces of attraction between water molecules
2.  Water moves upwards in the xylem against gravity in a continuous column
3.  evaporation/diffusion of water at -> a pressure difference -> pressure at xylem in roots -> pressure at xylem in leaves -> constantly moves upwards

Factors

Light Intensity

$\uparrow$Light Intensity -> $\uparrow$Photosynthesis -> $\uparrow CO_{2}$ in, $\uparrow O_{2}$ out -> $\uparrow$Stomata open -> $\uparrow$water diffusing out ->$\uparrow$transpiration

Temperature

$\uparrow$Temperature -> $\uparrow$Particles diffusion rate, $\uparrow$Air Capacity to hold water vapor -> $\uparrow$Evaporation rate -> $\uparrow$rate of transpiration
Until a certain temperature, plant dies

Wind Speed

$\uparrow$Wind Speed -> moves away the water particles surrounding the leaf -> $\uparrow$concentration gradient -> $\uparrow$rate of transpiration

Translocation

[!def]
Movement of sucrose and amino acids in the phloem from sources to sinks

==Source== (光合产物的源)
Part of the plant that releases sucrose or amino acids to be transported to other parts

==Sink== (光合产物消耗或储藏部位)
part of the plant to which sucrose or amino acids are being transported, and where they are used or stored