1. Transpiration

2. 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.

3. 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.

5. 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%

6. 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

7. 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

8. 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?

9. 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

10. 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 10

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

13. 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

14. 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).

15. Objective check in

16. 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?

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