Rate of transpiration Flashcards
What are the 2 types of factors effecting rate of transpiration?
Plant physiology and environmental
What are plant physiology factors?
Number, size and position of stomata, number of leaves and presence of cuticle
What are environmental factors?
Air movement/wind speed, relative humidity, temperature, light, soil water availability and carbon dioxide levels
What is light used for?
As an energy store for photosynthesis
How does light affect stomata?
Stomata open in light for gas exchange to get carbon dioxide in and oxygen out
What is te effect of increase is light intensity?
More stomata open
What is the effect of rate of transpiration with increased light intensity?
Diffusion of water vapour out increases so rate of transpiration increases
How is light intensity drawn?
It plateaus at a certain point as maximum rate of photosynthesis is reached
What is relative humidity?
Total amount of water vapour in the air of possible max water vapour air can hold
What is the effect of increased relative humidity?
More water vapour molecules therefore remain in air spaces inside the leaf
How does increased humidity affect rate of transpiration?
Transpiration rate decreases
What is the effect of increased temperature?
Increases kinetic energy so they infuse out more quickly
What is the effect of increased kinetic energy?
Increases rate of evaporation of after vapour molecules from spongy mesophyll cells into air spaces as the temperature increases, energy provided to break hydrogen bonds
What is the effect of temperature on relative humidity?
Temperature increases which increases max saturation of the air with water vapour molecules
What is still air?
Leaf/stomata has a layer of still air trapped by shape/hairs
What is the effect of still air?
Water vapour molecules diffuse out of the leaf and are trapped in still air so water vapour around stomata increases and air becomes more saturated
What is the effect of saturated air?
It decreases the water vapour diffusion gradient
How does air movement affect transpiration?
Increased air movement increases the rate of transpiration by maintains diffusion gradient
How do you measure transpiration?
A potometer
What is a potometer?
A device used for measuring the rate of water uptake of a leafy shoot
What is the cause of water uptake?
99% of water taken up is lost by transpiration
What is the stages of setting up a potometer?
- A cut plant stem is sealed into the potometer using a rubber bung.
- Air bubble is introduced to capillary tube and the distance the bubble travels shows how much water has been taken up
How can potometers measure effects on rate of transpiration
They can be set up in different environmental conditions
What are issues with setting up a potometer?
Air can enter the stem when its cut or air leaks in tubing
What are ways of reducing air entering set up?
Cut stem at angle under water and join to rubber tubing under water, seal the join between rubber bung and tubing with vaseline and use waterproof tape to seal the join between plant stem and rubber tubing
How can rate of transpiration be calculated?
By timing how long it takes the bubble of air to move a set distance (or vice versa)
How a the volume of water be calculated?
V = π x r² x l
Why does the potometer only gives an estimate of the rate of transpiration?
It measures water uptake and not all water taken up is lost as some is used in photosynthesis or making cells turgid
