Transpiration in flowering plants Flashcards
What is transpiration?
The loss of water from the plant
What is transpiration caused by?
Evaporation and diffusion of water from a plants surface - most transpiration happens in the leaves
What does the evaporation create?
A slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it
What does the more water drawn up from the roots cause?
A constant transpiration stream of water through the plants
What is a transpiration a side effect of?
The way leaves are adapted for photosynthesis
What is the importance of the stomata?
They let gases exchange easily - because there is more water inside the plant than in the air outside, the water escapes from the leaves through the stomata by diffusion
What four things affect transpiration?
- Light intensity - Temperature - Wind speed - Humidity
How does light affect transpiration?
-The brighter the light, the greater the transpiration rate Very little water escapes when the stomata closes when it gets dark. Photosynthesis cant happen in the dark so they don’t need to open to let out CO2
How does temperature affect transpiration?
- The warmer it is, the faster transpiration happens When its warm the water particles have more energy to evaporate and diffuse out of the stomata
How does windspeed affect transpiration?
- The higher the wind speed around a leaf, the greater the transpiration rate If it is windy the water vapour is swept away maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly from an area of high concentration to an area of low concentration
What happens if the wind speed is low around the leaf?
The water vapour just surrounds the leaf and doesnt move away. This means there a high concentration of water particles outside the leaf as well as inside the leaf so diffusion doesn’t happen as quickly
How does humidity affect transpiration?
- The drier the area around a leaf, the faster the transpiration happens If the air is humid theres a lot of water in it already so theres not much of a difference between the inside and outside of the leaf. Diffusion happens faster if theres a really high concentration in one place and really low concentration
What can be used to estimate transpiration rate?
A potometer
What is a potometer?
A special piece of apparatus used to estimate transpiration rates - it actually measures water uptake by a plant, but it is assumed that water uptake by a plant is directly related to water loss by the leaves (transpiration)
How do you set out a potometer?
