Download - Plant Transport
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Plant Transport
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Transport Overview
SugarsWater and minerals
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Vascular Tissue• Xylem
– Water– Dissolved minerals
• Phloem– Water– Sugars– Amino acids– Hormones
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Uptake of Minerals and Water• Lateral movement – soil to xylem
– Diffusion and active transport of minerals• Increased surface area
– Root hairs– Mycorrhizae
• Symplastic and apoplastic movement– All minerals must pass through a selective membrane– Casparian strip prevents direct apoplastic movement
into the xylem
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Lateral Transport of Minerals and Water from Roots
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Bulk Flow Transport Through Xylem
• Root pressure – pushing water– Active transport of minerals into root creates lower
water potential– Water enters cells and is pushed up xylem
• Transpiration – pulling water– Water evaporates from leaves– Water pulled up xylem because of cohesion of water
molecules– Transpiration controlled by openings in leaf called
stoma
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Transpiration
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Control of Transpiration• Stoma open
– K+ enter guard cell– Cell becomes turgid
from influx of water• Stoma closed
– K+ pumped out of guard cell
– Cell becomes flaccid from efflux of water
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Photorespiration• Response to high heat and low water• Stoma close to prevent water loss causing
low CO2 and high O2 levels in leaf• Carbon fixation low
– Carbon is removed from RuBP to produce CO2 – Rubisco runs in reverse
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Loading of Sucrose into Phloem
• Transport is in either direction at different times
• Transport from sugar source to sugar sink
• Sugar is pumped from source to sieve tube member
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Mass Flow in a Sieve Tube