Transpiration - Cohesion Tension Theory Flashcards
(20 cards)
Write all the components of a plant in order of top to bottom
Waxy cuticle
Upper epidermis
Palisade Mesophyll
Xylem
Phloem
Spongy mesophyll
Lower epidermis
Stomata and guard cells
Waxy cuticle
What does the waxy cuticle do
Prevents water loss (transpiration)
What is the upper epidermis
Transparent layer on top of the leaf to allow light through for photosynthesis
What is the palisade mesopyll
Where photosynthesis occurs
What is the spongy mesophyll
Where gas exchange occurs
What is the stomata
A pore in the lower epidermis which allows co2 and 02 to enter and leave
What are guard cells
Control opening and closing of stomata
Describe the cohesion tension theory
1: water evaporates from the mesophyll cells through stomata (transpiration)
2: which leads to a decreased water potential in the cell
3: therefore water enters from the cells next to it via osmosis
4: water forms a continuous unbroken stream thru xylem called the transpiration pull
5: water forms hydrogen bonds which stick together called cohesion
6: some water sticks to the xylem wall and pulls the xylem wall inwards known as tension
7: the transpiration pull will draw water from the soil into the root hair cells
Adaptations of the xylem
1: elongated tube made out of dead cells joined tg meaning there are no organelles that obstruct/ block the continuos flow of water
2: no end walls so no interrupted stream of water
3: thick walls made out of lignin which stops the xylem from collapsing due to water tension and cohesion
What is the assumption made when measuring the transpiration rate
Rate of uptake = rate of transporation
Why is the leaf shoot cut underwater in a potometer
To stop air from entering and forming more air bubbles
Why is the leaf short cut at an angle
To increase surface area
Why is a reservoir needed in a potometer
To carry out repeats of the experiment bcs u can more the air bubble back to the start
What are 2 adjustments made to the leaf shoot in a potometer
1: leaf shoot is cut underwater to prevent air from entering and forming more air bubbles;es
2: leaf shoot is cut at an angle to increase surface area
Formula for transpiration rate
Pi x r^2 x l / t (hours)
How does humidity affect the rate of transpiration
As humidity increases transpiration decreases because the water potential gradient b/w leaf and atmosphere is smaller reducing water loss.
In low humid the water potential gradient is larger causing more evaporation and therefore more transpiration
How does temperature affect the rate of transpiration
As temperature increases rate of evaporation also increases as the molecules in water gain more kinetic energy. The warm air also holds more moisture so increases the water potential gradient b/w leaf and air leading to a faster rate of transpiration
What are the 3 factors affecting transpiration
Light intensity
Temperature
Humidity
How does light intensity affect the rate of transpiration
As the light intensity increases the transpiration rate also increases. During the day when the light intensity is high the stomata opens to allow gas exchange for photosynthesis leading to water loss. So the greater the light intensity more stomata opens so more water is lost. High light intensity can also raise the temperature of the leaf
How does wind affect transpiration rate
wind removes the humid air around stomata.
This maintains a steep water potential gradient for faster diffusion of water vapour.
