B2.2.5/6 Transpiration Stream And Factors Affecting Transpiration Flashcards
Define transpiration
The loss of water from a plants leaves
The water lost must be replaced by uptake through roots
Transpiration stream
The constant flow of water from the roots through the xylem and out of the leaves
How does water enter the xylem
Diffuses from the soil into the root hairs by osmosis
Once inside the xylem the water can be transported throughout the plant
How is water lost from leaves
While the stomata are open, water evaporates from cells inside the leaf
This creates a concentration gradient between the air inside the leaf and the surrounding air
Water then diffuses out of the leaf
How is uncontrollable water loss prevented
The upper surface of many leaves is covered in a waxy waterproof layer, the waxy cuticle
Most stomata are found on the underside of the leaf
Why do plants wilt
If it loses water faster than it takes in it may wilt
The leaves collapse and drop
This greatly reduces surface area available for evaporation
How do they prevent further water loss
Stomata closes
Plant will remain wilted and will eventually die if it doesn’t receive water but reducing the temperature and light intensity can help to keep it alive for longer
Potometer
Take an air bubble into the capillary tube
As water moves into shoot and evaporates from its leaves, the air bubble moves towards the plant
Measure how fast the air bubble travels
This will give you an idea of how fast the plant is transpiring
Refill capillary tube and repeat. You can change conditions or see how they affect transpiration
Rate of movement formula
Distance/time
Which factors affect rate of transpiration
Light intensity
Air movement
Temp
Humidity
How does light intensity affect transpiration
Stomata open in the light and close in dark
If you increase light intensity, more water evaporates
Try rate of transpiration increases until all stomata are open -it’s now at max rate
How does temp affect transpiration
If you increase temp, water evaporates more quickly from leaf cells
Diffusion of water vapour out of the leaf becomes more rapid
This increases rate of transpiration
How does air movement affect transpiration
When air moves over the surface of the leaf, it moves evaporated water molecules away from the leaf
The faster the air moves, the faster the molecules are moved
This increases concentration gradient between leaf and air since fewer water molecules are present on air compared to in leaf
This means water diffuses quicker out of leaf
How does humidity affect rate oftranspiration
Humidity is the amount of water in the air
The higher the humidity, the more water it contains
If you decrease humidity, this increases concentration gradient between leaf and air so water diffuses put wuicker
Increasing rate of transpiration
