Transpiration

Objective 6.L.1.2: I can explain the significance of transpiration to the survival of the plant. I can explain the structures used in transpiration.

Definition Transpiration is the evaporation of water from the aerial parts of plants. Of all the water plant absorbs, over 90% is transpired to the air as water vapor.

From where water is transpired? Aerial parts (parts surrounded by air) Stomatum (stomatal transpiration) ~ 90% Lenticels (raised pores on stem) 0.1% Cutin (waxy, water repellent part of cell walls) 3%~10%

What is this process called? Stomatal Transpiration What is most likely leaving through the stomata of the leaf picture here? Water (H2O) What is this process called? Stomatal Transpiration 6

Stomatal transpiration Cuticle Prevents water loss Mesophyll Site of photosynthesis Stomata Guard cells Openings allow gases and water to move in and out of leaf Open and close the stomata

Transport in plants H2O & minerals Sugars Gas exchange transport in xylem transpiration evaporation, adhesion & cohesion negative pressure Sugars transport in phloem bulk flow Calvin cycle in leaves loads sucrose into phloem positive pressure Gas exchange photosynthesis CO2 in; O2 out stomates respiration O2 in; CO2 out roots exchange gases within air spaces in soil Why does over-watering kill a plant?

Function of Stomata These stomata (leaf openings) naturally allow water to evaporate out. Why would the plant close stomata with guard cells? Prevent excess water loss through transpiration. (conserve water) So what is the point of having stomata? Allows gas exchange for photosynthesis Guard Cells Stoma Open Stoma Closed Guard cells open by inflating with extra water. They do this by pumping K+ ions into the cell, which causes water to rush in via osmosis to diffuse the high ion concentration. 9

How do the guard cells react to the availability of water? Function of Guard Cells How do the guard cells react to the availability of water? Dry – guard cells CLOSE lots of H2O – guard cells OPEN http://www.ualr.edu/~botany/images.html 10

Factors influencing stomatal aperture Light Temp. CO2 Water content Plant hormone

The driving force of transpiration is the “vapor pressure gradient The driving force of transpiration is the “vapor pressure gradient.” This is the difference in vapor pressure between the internal spaces in the leaf and the atmosphere around the leaf Diffusional resistance comprises stomatal resistance and boundary layer resistance

If you were an aquatic plant where would your stomata be? Fringed Water-lily Stomata are found only on the upper epidermis because the lower epidermis is submerged in water. If the stomata were to be on the underside, they wouldn't be able to perform their function (i.e to allow water to evaporate and thus contribute to transpiration).

Objective check in

What parts of the plant allow water to move in the plant? Objective 6.L.1.2: I can explain transpiration. Objective 6.L.1.2 I can identify the structures used in transpiration. Why do plants wilt? What parts of the plant allow water to move in the plant? What cell parts regulate water evaporation?

Lets see it in action - transpiration lab. Observe Celery Stalk. Answer the Questions