Transpiration and stomata

Created by

Sadiya Uddin

Cards (10)

Transpiration 
The process of water movement through a plant and its evaporation from aerial parts, especially leaves
Stomata 
Pores in the surface of a leaf or stem through which gases and water vapour pass
Factors affecting transpiration rate 
Light intensity
Temperature
Air flow
Humidity
Light intensity 
Stomata begin to close as it gets darker
The brighter the light, the greater the transpiration rate
Temperature 
The warmer it is, the faster transpiration happens
Water particles have more energy to evaporate and diffuse out of the stomata
Air flow 
The better the air flow around a leaf, the greater the transpiration rate
If air flow is poor, water vapour just surrounds the leaf and doesn't move away, so diffusion doesn't happen as quickly
If there's good air flow, the water vapour is swept away maintaining a low concentration outside the leaf, so diffusion happens quickly
Humidity 
The drier the air around a leaf, the faster transpiration happens
If the air is humid, there's not much of a difference between the inside and the outside of the leaf, so diffusion doesn't happen as quickly
Measuring transpiration rate 
1. Set up apparatus with air bubble
2. Record starting position of air bubble
3. Start stopwatch and record distance moved by bubble per unit time
4. Keep conditions constant throughout experiment
Guard cells 
They have a kidney shape which opens and closes the stomata
When the plant has lots of water, the guard cells fill up and become plump, opening the stomata
When the plant is short of water, the guard cells lose water and become flaccid, closing the stomata
Thin outer walls and thickened inner walls make the opening and closing work
They're sensitive to light and close at night to save water without losing out on photosynthesis
There are usually more stomata on the undersides of leaves than the top
Guard cells are adapted for gas exchange and controlling water loss within a leaf