Stages of Transpiration 1. Water uptake from soil. o Roots absorb water . o Water flows into root cells by osmosis. 2. Cohesion and adhesion to xylem. o Cohesion in xylem causes water to form a

continuous stream. (Brooker , et. al 2008)

o Water molecules carry a slight electric charge causing attraction which links molecules in long chains.

o Surface tension increases in the intercellular spaces of cells, pulling on water stream in xylem. (Brooker , et. al

2008)

3. Transpiration o Water is transported through xylem (long

continuous tubes). o Water escapes the leaves through microscopic pores

called stomata. o As each molecule breaks loose it pulls up another

molecule to create a continuous pulling tension all the way down the xylem to the root.

http://0-www.fofweb.com.lib.epcc.edu:80/activelink2.asp?ItemID=WE40&SID=5&iPin= WCR0766&SingleRecord=True.

XYLEM

•A plant vascular tissue that conducts

water, minerals, and organic

compounds. (Brooker, et. al 2008)

•Non-living tissues

•More than 90% of water transpired from

plants is lost through the stomata.

•Stomata closes to retain water.

•Stomata closes to allow entry of CO2 needed

for photosynthesis and to allow oxygen and

water vapor to exit.

(Brooker, et. al 2008)

Elizabeth Gallardo 2009

Water Potential and the leaf

Evaporation from the leaf sets up a water potential gradient

between the outside air and the leaf's air spaces. The gradient is

transmitted into the photosynthetic cells and on to the water-

filled xylem in the leaf vein. (Wallace) http://home.earthlink.net/~dayvdanls/plant_transport.html

Cross Section of oak Xylem

STOMATA

Facts about Transpiration: Water vapor from plant transpiration is an important source

of rainfall. (¾ of rainfall received by the Amazon tropical

rain forest comes from plant-transpired water vapor, it is

visible as a mist.) (Brooker, Widmaier, Graham, Stiling 2008)

It cools plant surfaces, local and global climate. (Brooker, e t. al 2008)

99% of water entering plants is lost as vapor during

transpiration. (Brooker, e t. al 2008)

A typical tree loses 400 L of water per day through

transpiration. (Brooker, e t. al 2008)

Transpiration is affected by heat:

The force can be so strong that on a hot day, when the

evaporation rate from the leaves is very high, water moves

through the plant at up to 30 inches (76 cm) a minute and

the sides of the xylem vessels are pulled in, making a

measurable difference in the diameter of the stem. (http://0-www.fofweb.com.lib.epcc.edu/activelink2.asp?ItemID=WE40&SID=5&iPin=EWCR0766&SingleRecord=True)

Stomata are small openings

found on the underside of

leaves that are connected to

vascular plant tissues. http://www.physicalgeography.net/fundamentals/8i.

html

Diagram abstracted from http://0-www.fofweb.com.lib.epcc.edu/Electronic_Images/Onfiles/SVRbio134.pdf

PHLOEM

•It is a specialized conducting tissue at the

center of the plant’s stem.

•Phloem loading-is the process of conveying

sugars to sieve-tube elements for long-distance

transport.

(Brooker, et. al 2008)

•Tall trees are able to transport water and

minerals to amazing heights and in some cases

more than 110 m.

•They are able to do this through an extensive,

branched, long-distance vascular system made

up of xylem and phloem tissues.

•Bulk flow-is the mass movement of liquid in

a plant caused by pressure, gravity, or both.

(Brooker, et. al 2008)

Phloem

BULK FLOW