Transpiration Flashcards
What is transpiration
Transpiration is the loss of water vapour from the surface of the plant leaves
Describe the process of transpiration/transpiration stream
Transpiration starts with the evaporation of water from cells inside the leaf.
The water vapour then diffuses through the air spaces in the spongy mesophyll and out of the leaf through the stomata
Now water passes from the xylem into the leaf to replace the water that has been lost.
Water is drawn into the root hair cells and up the xylem vessels to the leaf
Where does photosynthesis take place
Photosynthesis takes place in the palisade mesophyll
How does water enter the roots of a plant
Water enters the roots of a plant through root hair cells
Why is transpiration important
Transpiration is important as it brings water to the leaf. Water is required for photosynthesis
The transpiration stream transports dissolved mineral ions such as magnesium which play important roles in the plant
The evaporation of water from the leaf cools the leaf down, especially in warm weather.
Factors that affect transpiration
Light intensity
Temperature
Air movement
Humidity
How does temperature affect the rate of transpiration
The rate of transpiration is greater in higher temperatures. This is because evaporation and diffusion are faster at higher temperatures
How does humidity affect the rate of transpiration
Transpiration is slower in humid conditions ( not dry conditions)
This is because the diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air
Diffusion happens faster if there is a really high concentration in one place and a really low concentration in the other
How does air movement affect the rate of transpiration
The rate of transpiration increases in windy conditions
This is because water vapour is removed quickly by air movement, speeding up diffusion of more water out of the leaf
How does light intensity affect the rate of transpiration
The rate of transpiration increases when the light intensity increases.
This is because the stomata (openings in the leaf) open wider to allow more carbon dioxide into the leaf for photosynthesis. Once the stomata have opened, water vapour can now pass out of the leaf.
What are stomata surrounded by
Stomata are surrounded by two guard cells
What happens to guard cells when exposed to a high light intensity. How does this effect the stomata
When the light intensity is high (e.g. during the day), the guard cells swell and change their shape. This causes the stomata to open. Now carbon dioxide can diffuse into the leaf and can be used for photosynthesis.
What does the plant do to it’s stomata in hot conditions
In hot conditions, the plant closes its stomata to reduce water loss by transpiration.
This means that the plant cannot photosynthesise
How do plants have adaptations for controlling water loss - help them to photosynthesise as much as possible while losing as little water as possible
Most leaves have a waxy, waterproof layer (the cuticle) to prevent the uncontrolled water loss. In very hot environments, the cuticle may be very thick and shiny.
Most of the stomata are found on the underside of the leaves. This protects them from the direct light and energy from the Sun.
What do plants do if they begin to lose water faster than it is being repaced by the roots
The whole plant may wilt
The leaves will all collapse and hang down
This greatly reduces the surface area available for water loss by evaporation.
