Transpiration, Translocation and the Stomata Flashcards
what is the role of phloem tubes?
*They transport food (sugars)made in the leaves to the rest of the plant for imimediate use or for storage.
*the transport goes in both directions in a process called translocation
what is the role of xylem tubes?
•They carry water and mineral ions from the roots to the stemn and leaves.
•This is called the transpiration stream.
what is transpiration?
1)Transpiration is caused by the evaporation and diffusion of water from a plant’s surface
2) This evaporation creates 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.
3) This in turn means more water is drawn up from the roots and theres a constant transpiration stream through the plant
where does transpiration occur?
mostly at the leaves
how does water escape from the leaves?
by diffusion as there is more water inside the plant than outside so water escapes from the leaves through the stomata by diffusion
when do stomata close?
Stomata begin to close as it gets darker. Photosynthesis can’t happen in the dark, so they don’t need to be open to let CO, in. When the stomata are closed, very little water can escape.
what factors affect transpiration rate?
1) LIGHT INTENSITY - the brighter the light, the greater the transpiration rate.
2) TEMPERATURE - the warmer it is, the faster transpiration happens.
3)HUMIDITY - the drier the air around a leaf, the faster transpiration happens.
4) AIR FLOW - the better the air flow around a leaf (e.g. stronger wind), the greater the transpiration rate
how does temperature affect transpiration rate?
When it’s warm the water particles have more energy to evaporate and diffuse out of the stomata.
how does airflow affect 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 air flow, the water vapour is swept away, maintaining a low concentration of water in the air outside the leaf.
•Diffusion then happens quick from an area of higher concentration to an area of lower concenfration.
how does humidity affect rate of transpiration ?
•the drier the air around a leaf, the faster transpiration happens.
•If the air is humid there’s a lot of water in it already, so there’s not much of a difference between the inside and the outside of the leaf.
•Diffusion happens fastest if there’s a really his concentration in one place, and a really low concentration in the other.
how can you estimate the rate of transpiration?
you can measure the uptake of water by a plant by setting up a potometer and recording the starting position of air bubble. you would then use a stopwatch to record distance moved by bubble per unit at a time
how are guard cells adapted to open and close stomata?(5)
1) They have a kidney shape which opens and closes the stomata in a leaf.
2) When the plant has lots of water the guard cells fill with it and go plump and turgid.This makes the stomata open so gases can be exchanged for photosynthesis.
3) When the plant is short of water, the guard cells lose water and become flacold, making the stomata close. This helps stop too much water vapour escaping.
5) They’re are sensitive to light and close at night to save water
7)You usually find more stomata on the undersides of leaves than on the top. The lower surface is shaded and cooler - so less water is lost through the stomata than if they were on the upper surface.
