Xylem and phloem + water movement

Cba to describe it

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Functions of xylem and phloem

Xylem= transports water and mineral ions up the plant

Phloem= transports assimilates up and down the plant

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Locations of xylem and phloem (dicot)

                     Stem                                       Roots                                                Leaves

Xylem         Inside the vascular bundle               X-shaped                               At the top of the phloem

Phloem     Outer edge of vascular bundle           Around the xylem                     Under the xylem

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Structure of xylem and phloem

Xylem                                                                                          Phloem                                                               

Lignified cell walls  (to keep water in the vessels)                                Made of sieve tube elements

Dead cells                                                                                 Live cells

No companion cells                                                                     Companion cells 

No contents                                                                               Few contents

Tube shaped                                                                             Also tube shaped

Pitted walls (to allow movement of water in and out)                    Sieve tube elements attached to companion                                                                                         cells and linked by plasmodesmata

No membrane bound organelles                                                   Small cytoplasm  

                                                                                         Sieve tube elements have no nucleus       


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Symplast= through cytoplasm then through plasmodesmata from cell to cell

Apoplast= through cell wall but is eventually clocked by casparian strip 

Vacuolar= through vacuole

Casparian strip= Blocks the apoplast pathway near the end so water molecules then follow symplast

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Water potential

Trident symbol represents water potential \Psi (http://upload.wikimedia.org/math/3/9/8/398b8c3e58e961cdea0fe626771f3243.png)

Definition= Measure of the tendency of water molecules to diffuse from one place to another

The higher the concentration of dissolved substances in the water, the lower the water potential

Hypotonic= Less water than solute

Isotonic= Equal amounts of water and solutes

Hypertonic= More solutes than water

Water molecules move from less negative regions (higher water potenial), to more negative regions (lower water potential)

In plant cells \Psi (http://upload.wikimedia.org/math/3/9/8/398b8c3e58e961cdea0fe626771f3243.png) is always negative because they contain assimilates

\Psi (http://upload.wikimedia.org/math/3/9/8/398b8c3e58e961cdea0fe626771f3243.png) of pure/distilled water is 0

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