Transport in plants

The structure and function of the xylem and phloem vessels, transpiration, translocations & adaptions of xerophytes.

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  • Created by: LexiLNye
  • Created on: 24-01-14 15:56
Function of xylem
To transport water and minerals around plant by transpiration
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Function of phloem
To transport assimilates (e.g Sucrose) by translocation
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Function of cambium
Layer of meristem cells between xylem and phloem, which can divide to produce more xylem + phloem.
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The unavoidable loss of water from a plant through the stomata in the leaves (loss of water vapou from the aerial parts of a plant- as a consequence of stomatal opening for gas exchange, necessary for photosynthesis)
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The transport of orangic solutes (Assimilates) through a plant via the sieve tube elements of phloem tissue by MASS FLOW
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External factors affecting transpiration
Light intensity, Temperature, Humidity, Wind & Water availability
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Internal factors affecting transpiration
Number of leaves, Density and distribution of stomata, Thickness of waxy cuticle, Roots
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What are xerophytes?
Plants that are adapted to reduce water loss (as they live in dry conditions: e.g sand dunes, frozen plains, deserts)
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What do the xeromorphic adaptions do?
Reduce the water vapour potential gradient between the plant and the atmosphere.
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Examples of xerophytes
Cactus, Marram Grass, Succulent plants (e.g Aloe vera)
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Adaptions of Marram grass
1) Leaf rolled up to trap air inside- HInge cells 2) Hairs - reduce movement of air trapped in the centre with high water potential and 3) Sunken stomata (in pits) to trap moist air close to the stomata - reduces water vapour potential gradient
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Adaptions of Cactus
1) Small surface area minimised evaporation- have ridges that tighten the stem (reduces water loss) 2) Spines instead of leaves 3) Stems that can store water 4) Widespread root system
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Where substances are made or stored, and loaded (actively) into sieve tube elements (E.G leaves, tubers)
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Where the substances are removed (actively/ by diffusion) for use and storage (E.G Root tips, roots, meristems, developing buds)
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Phloem sap contains?
Sucrose, Ions (K, CI, NO3, PO4, Mg, Na, Ca), Amino Acids, Adenosine tri phosephate (ATP), Growth substances (auxins, cytokinins)
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Increase in hydrostatic pressure is in
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Decrease in hydrostatic pressure in
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Sucrose is loaded into companion cells by...?
1) Hydrogen (proton) pump -active transport. 2) Co-transporter protein - faciliated diffusion
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1) Hydrogen (proton) pump -active transport
Pumps H ions actively out of companion cells. Requires engery (ATP). Creates high conc of H ions in mesophyll issue OUTSIDE companion cells.
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2) Co-transporter protein - faciliated diffusion
H ions diffuse (re-enter) into the companion cell down a conc gradient. Transports sucrose simultaneously against conc grandient- co - transport
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Evidence FOR mechanism of translocation
Ringing a tree (girdling), Radioactive carbon tracing, Aphids (insects),
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Card 2


Function of phloem


To transport assimilates (e.g Sucrose) by translocation

Card 3


Function of cambium


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