Water uptake + movement up the stem

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  • Created by: Steff06
  • Created on: 27-03-16 15:57
Where are root hairs and what do they do?
In the epidermis. The root hair cells increase surface area of the root.
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How do cells absorb minerals from the soil?
By active transport using ATP energy.
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What effect do minerals have on the cell cytoplasm?
Minerals reduce the water potential of the cell cytoplasm so water is taken up across the plasma membrane by osmosis as the molecules move down the water potential gradient.
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What is the endodermis and what does it consist of?
It is a layer of cells surrounding the xylem. It consists of special cells that have a waterproof ***** in some of their walls - known as the Casparian *****.
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What does the casparian ***** do?
Blocks the apoplast pathway, forcing water into the symplast pathway.
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How do endodermis cells move minerals and where do they take them from and to?
Move minerals by active transport from the cortex into the xylem.
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What effect does moving the minerals have on the xylem?
It reduces the water potential in the xylem so water moves from the cortex through the endodermal cells into the xylem by osmosis.
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What is the effect of the cells moving by osmosis?
Reduces the water potential of cells just outside the endodermis which creates a water potential gradient across the whole cortex.
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After the water potential gradient is created across the cortex where is the water moved?
Along the symplast pathway from the root hair cells across the cortex and into the xylem.
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As water is moved along the symplast pathway, what happens at the same time?
Water can move through the apoplast pathway across the cortex.
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After the water has moved across the cortex, where does it move next?
It moves into the cells to join the symplast pathway just before passing through the endodermis.
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What is the role of the Casparian *****?
To block the apoplast pathway between the cortex and xylem.
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What does blocking the apoplast pathway ensure?
Water and nitrate ions have to pass into the cell cytoplasm through cell membranes.
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What are present in the cell membranes and what do these do?
Transporter proteins are in the cell membranes. Nitrate ions are actively transported from the cytoplasm of cortex cells into the xylem.
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What do actively transporting the nitrate ions cause?
Causes the water potential to reduce in the xylem so water from cortex cells flows into the xylem by osmosis.
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What happens once water has entered the xylem?
It cannot pass back into the cortex as the apoplast pathway of the endodermal cells is blocked.
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What are the 3 processes that help to move water up the stem?
Root pressure, transpiration pull and capillary action.
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Describe the action of root pressure
Action of endodermis moving minerals into xylem by active transport drives water into the xylem by osmosis which forces water into the xylem and pushes water up the xylem.
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How much can root pressure push water up the stem?
A few metres up the stem, but cannot account for water getting to the top of tall trees.
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What is the effect of transpiration pull?
Loss of water by evaporation from leaves must be replaced by water coming from the xylem. Water molecules are attracted to each other by cohesion.
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What is the role of cohesion?
Cohesion bonds are strong enough to hold molecules together in a long chain which creates the transpiration stream.
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What can the pull from above create?
Can create tension in the column of water which is why xylem vessels must be strengthened with lignin.
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What does lignin do?
Prevents vessels from collapsing under tension (cohesion-tension theory). Relies on plant maintaining an unbroken column of water all the way up the stem.
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What happens if the water column is broken in 1 xylem vessel?
The water column can still be maintained through another vessel via the pitts.
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What does capillary action do?
The same forces that hold water molecules together also attract the water molecules to the sides of the xylem vessel.
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Why does this force of attraction have this effect?
Because the xylem vessels are very narrow, so the forces of attraction can pull the water up the sides of the vessel.
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How does most water leave the leaf?
Most water that leaves the leaf exits through the stomata which are tiny pores in the epidermis.
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Where does a tiny amount of water leave through?
A tiny amount of water leaves through the waxy cuticle. Water evaporates from the cells lining the cavity below the guard cells.
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What does this evaporation of water cause?
Water potential to lower causing water to enter them by osmosis from neighbourhing cells.
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How does water enter these cells?
From cells deeper in the leaf until water leaves the xylem and enters into the innermost leaf cells.
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Other cards in this set

Card 2

Front

How do cells absorb minerals from the soil?

Back

By active transport using ATP energy.

Card 3

Front

What effect do minerals have on the cell cytoplasm?

Back

Preview of the front of card 3

Card 4

Front

What is the endodermis and what does it consist of?

Back

Preview of the front of card 4

Card 5

Front

What does the casparian ***** do?

Back

Preview of the front of card 5
View more cards

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