Transpiration Module 10 Flashcards
Leaf gas exchange
Control of gas exchange through the stomata
90% occurs through the stomata, 5-10% occurs through the cuticle, this can vary depending on the size of the cuticle
How does the stomata regulate gas exchange
When they are open water evaporates and CO2 is able to enter for photosynthesis and calvin cycle
When they close water is conserved but CO2 cannot enter
Transpiration is what?
The loss of water through the leaf(its a process)
What is the best control for water loss?
Having less stomatas and closing the stomata
Carbon Dioxide Exchange
approximately 0.04% of air is CO2
CO2 enters through the stomata which drives PS
increasing CO2 entry is accomplished by opening the stomata or increasing number of stomata
When does the atmosphere have more CO2?
In north America it is in December and January because the plants drop their leaves and don’t use CO2
Cost/benefit of Gas Exchange
for every gram of CO2 fixed, the plant loses 250-600g of water
plants are constantly balancing water loss with CO2 entry by controlling the stomatal openings
Function of Transpiration
beneficial, keeps water column intact and moving
cools the leaf by 10-15 degrees celcius
moves nutrients (and herbicides) in transpiration streams from soil to leaf
no energy is required
enables capture of nutrients from a volume of soil
Transpiration Processes
Evaporation and Diffusion
Evaporation
takes place in the sub-stomal chambers
Inside the leaf, water is taken from surrounding cells
this creates a chain reaction, takes from the stem, from the roots, from the soil
Diffusion
the movement of molecules from a region of high to low concentration (dye in water)
as water is diffusing out, CO2 molecules are diffusing into the leaf
Environmental factors that affect transpiration
Temperature
Humidity
Wind
Light
Temperature Factor
very important
evaporation rate doubles per 10C rise in temp, up until a point
transpiration increases with air temperature (until 30 to 35C)
if moisture is available leaf temperature probably does not exceed 30-35C due to evaporative cooling
if restricted, leaf temp will rise
Humidity Factor
refers to the amount of water in the air
transpiration is higher if air in stomates is moist and outside air is dry
Wind Factor
transpiration increases on windy days
air currents move water vapour away from the leaf
affected by the leaf shape, pubescence (little tiny hairs that can block wind, a boundary layer)
Light Factor
light striking a leaf tends to increase leaf temperature, this increasing transpiration rates
light increases PS, which decreases CO2, which causes stomates to open
Daily cycle of transpiration for most plants
early in the morning the day is cooler (low transpiration rate)
midday the stomates close to avoid excessive water loss
later in the day, it is cooler, stomates open
dark period stomates are closed, plants can’t use CO2 at night
Hanging Laundry
think about how quickly clothes dry when they hang outside
sunny quickly
cold wet slowly
transpiration is low at night
When do cacti transpire?
at night
it’s very hot and sunny during the day so they save water and then transpire at night
Midday wilting
transpiration in plants is greatest on moist soils on hot, sunny, windy days
transpiration may exceed the plant’s ability to take up water, and midday wilt occurs
leaves wilt but they may still photosynthesize
overnight the plant moisture is replenished (water is taken up by roots)
if a plant remains wilted overnight, then the plant has severe water deficits (heat stress)
What features do plants have to regulate water loss? (8)
1.reduce stomate numbers (reduces CO2)
2.stomates on the lower leaf surface
3.sunken stomata
4.epidermal hairs (reduces wind velocity against the opening)
5.bulliform cells (plant can roll to reduce SA and light interception)
6.thickened cuticle
7.lower SA surface:volume ratio (pines)
8.C3 vs C4 vs CAM
C3 vs C4 bs CAM
C3 is plant like wheat and cereals
C4 is tropical plants, can withstand drought
CAM is cacti
How does water move through plant parts?
Water pull, root pressure, and capillary action
What is water pull?
as each water molecule evaporates into the substomatal chamber, it pulls another water molecule from below
water is sucked through the plant
possible because of the cohesive properties of water
no energy is required
water columns of cut twigs recede quickly
tree trunk is smaller during the day
