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Flashcards in water transport in plants Deck (11)
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what is root pressure

can be demonstrated by cutting off the shoot of a plant at soil level. fluid will exude from the xylem
- the pressure of the fluid being pushed out of the cut xylem can be measured
- we know it is an active process


what is the endodermis

- waxy, water repellent band called the casparian strip in its cell wall. this forces water in the root travelling towards the xylem to leave the vacuolar pathway and pass through the endodermis cell membrane


how is root pressure created

- active transport of mineral ions into xylem by endodermal cells creates less negative water potential in xylem
- due to casparian strip all water is passing through the endodermal cells
-this water now moves into xylem by osmosis down the water potential gradient
- this creates force that helps move water up then xylem of the plant
- this is root pressure


what is cohesion

the forces of attraction between like molecules


what is adhesion

the forces of attraction between 'unlike' molecules


what is capillary action

if a narrow tube is placed in a beaker of water the water rises up the tube by capillary action


what is cohesion-tension theory

a wide capillary tube has a small surface area to volume ratio; a relatively small number of molecules in contact with the wall of the tube are trying to pull (cohesion) a relatively large number of molecules up the tube
a small capillary tube has a large surface area to volume rating this means a large number of molecules in contact with the wall of the tube (adhesion) are pulling a small number of water molecules up the tube


what are xylem vessels

very narrow and form continuous columns up the stem due to the loss of their end walls
they act as capillary tubes which support long columns of water
if air bubbles form in a xylem vessel (which breaks the column of water) it can move through a pit into an adjacent vessel
water being lost from the leaves pull the water out of the xylem in the leaves and this force is passed down the xylem due to cohesion


what is a transpiration stream

movement of water vapour down its concentration gradient from the air spaces in the leaf through the stomata
the water has evaporated from the surface of the mesophyll cells
water in the xylem of the leaf travels to the spongy mesophyll cells by osmosis down the water potential gradient


what is transpiration

- movement of water vapour out of a leaf down a water potential gradient through the stomata
water evaporates from the surface of the spongy mesophyll cells into the air spaces in the leaf
this means there is higher concentration of water vapour in the leaf than outside the leaf
water vapour infuses through the stomata


what is a potometer

used to measure the transpiration rates from plant shoots
as water vapour transpires from the leaves it is replaced by water from the capillary tube
this can be recored as the movement of the air bubble in a known period of time
opening the tap on the reservoir allows the air bubble to be returned to the end of the capillary tube so repeats can be taken