Transpiration and Stomata Flashcards
What is the transpiration rate affected by ?
- Light intensity
- Temperature
- Air flow
- Humidity
How does Light intensity and Temperature affect transpiration rate ?
Light intensity : Brighter light, greater transpiration rate . Stomata closes as it gets darker . Photosynthesis can’t happen in the dark as they don’t need to open to let co2 in. when stomata are closed, very little water can escape
Temperature : Warmer it is, faster transpiration happens faster. When its warm, the water particles have more energy to evaporate and diffuse out of the stomata
How does Air flow and Humidity affect transpiration rate ?
Air flow : The better the airflow around a leaf, greater the transpiration rate. If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away. This means there’s a high concentration of water particles outside the leaf as well as inside it, so diffusion doesn’t happen as quickly. If there’s good airflow the water is swept away quickly, maintaining a low conc of water in the air outside the leaf. Diffusion then happens quickly, from an area of high conc to an area of ,ow conc.
Humidity : The drier the air around the leaf, the faster transpiration happens .
This is what happens with airflow . If the air is humid there’s a lot of water in it already so there’s not much of a difference between inside and outside of the leaf. Diffusion happens fastest if there’s a really high conc in one place and a really low conc in the other
How to estimate the rate of transpiration
1) measure uptake of water by plant. This is because you can assume uptake of water by plant is directly related to water loss by leaves
Set up apparatus ( Check page 41) and then record starting position of air bubble . Start a stopwatch and record the distance moved by the bubble per unit time. e.g. per hour . Keep conditions constant throughout your experiment, e.g. the temperature and air humidity
Check page 41 and memorise diagram
guard cell functions and what occurs when plant has lots of water and short of water
Kidney shape which opens and closes the stomata
When plant has lots of water, the guard cells fill with it and go plump and turgid. This makes stomata open up so gases can be exchanged for photosynthesis
When plant is short of water, guard cells lose water and become flaccid , making the stomata close. This helps stopping too much water vapour escaping.
Thin outer walls and thickened inner walls make the opening and closing work.
What are guard cells sensitive to ?
light and close at night to save water w/o losing out on photosynthesis
You can usually find more stomata on under side of leave rather than on top. The lower Surface is shaded and cooler – so less water is lost through the stomata then if they were on the upper surface.
Guard cells are therefore adapted for gas exchange and controlling water loss within a leaf.
