Movement of water through roots

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  • Created by: Alice
  • Created on: 30-05-14 11:26
What is the job of root hair cells?
Plant exchange surfaces responsible for water and ion absorption
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Why must they bring water into the plant?
Must replace water lost by transpiration.
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Why are root hairs efficient surfaces for water and ion exchange?
Large SA - fast diffusion rate from being very long. Thin surface area, so short diffusion rate
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How does water reach the root hair cell?
Soil is mainly water - higher water potential than in cell - creates water potential gradient and water moves into the root by osmosis which is more negative
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What are the two pathways the water then follows?
Apoplastic and Symplastic Pathways
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What happens in the apoplastic pathway?
Water drawn into endodermal cells, pulls water along cohesively (molecules stick together) through cell walls from tension created. Walls are made of mesh-like cellulose which has little resistance.
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What happens in the symplastic pathway?
Water moves by osmosis into root hair cell - high water potential, less negative so creates a water potential gradient as cortical cells are more negative in terms of water potential. Creates continuous column of water through cytoplasms with WP grad
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How does the casparian strip come into play?
Apoplastic pathway's movement of water is blocked by waterproof Casparian ***** which diverts the water to the cytoplasm with symplastic pathway water
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How is water transported into the xylem?
Active transport of ions and salts into xylem creates more negative water potential. Establishes water potential gradient so water moves in by osmosis to dilute xylem - creates ROOT PRESSURE, helping water move up the plant
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How does water move through the stomata?
Guard cells open and close stomata. If stomata open, water diffuses out of air spaces into air. Water which is lost from air spaces is replaced by evaporating water from mesophyll cells.
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What happens when there is a change in the size of stomatal pores?
There is a change in the rate of transpiration
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How does water move up the stem in the xylem?
Cohesion tension theory - water molecules stick together due to hydrogen bonds and create continuous column. Tensions between each molecule allows transpirational pull to make negative pressure and pull the molecules up the plant.
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How does water move across leaf cells?
Water lost from mesophyll to air spaces. Mesophyll cells have lower water potential so water enters by osmosis and establishes water potential gradient from neighbouring cells. Pulls water across the leaf from xylem then out to the atmosphere.
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Other cards in this set

Card 2

Front

Why must they bring water into the plant?

Back

Must replace water lost by transpiration.

Card 3

Front

Why are root hairs efficient surfaces for water and ion exchange?

Back

Preview of the front of card 3

Card 4

Front

How does water reach the root hair cell?

Back

Preview of the front of card 4

Card 5

Front

What are the two pathways the water then follows?

Back

Preview of the front of card 5
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