B2.2.5 - Transpiration Stream Flashcards Preview

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What causes water to move through xylem vessels?



What is transpiration?

The process where plants lose water which is then replaced by uptake of the roots


What is a transpiration stream?

The constant flow of water from the roots, through the xylem and out of the leaves


How does water enter the xylem vessels?

It diffuses into the root cells via osmosis, and then moves from cell to cell until it reaches the xylem vessel


What does the stomata do?

Allows carbon dioxide to diffuse in for photosynthesis


What cells allow the stomata to open or close?

Guard cells


What happens to the water when the stomata is open?

It evaporates from cells inside the leaf into the leaf’s air space, which creates a concentration gradient between the air and the leaf.


What happens to the water once the concentration gradient is formed?

The water vapour inside the leaf, which is high concentration, diffuses into the air, which is low concentration.


What does the loss of water in the vessels mean?

It means the pressure in the vessel in the leaf is reduced


Describe the process of transcription.

When a stomata opens, the water on the surface evaporates into the leaf’s air space. This creates a concentration gradient, so the water can diffuse through the leaf and outside. This water loss reduces the pressure at the top of the xylem vessel, allowing the water to flow upwards from high to low pressure.


What do most leaves have to prevent uncontrollable water loss?

The cuticle (waxy waterproof layer on the upper surface)


What is the cuticle like in hot environments?

Very thick and shiny


Where are most stomata found on a leaf?

On the underside


What happens when a plant loses water faster than it can take in?

It wilts


Why does the evaporation greatly decrease when a plant wilts?

Its leaves droop, which greatly reduce the surface area for respiration


What will help a wilted plant stay alive for longer?

Reduced light intensity
Reduced temperature