Transport_in_stems - Ioana Dobre Transport in stems-Xylem transports water and minerals to leaf and is essentially passive Phloem = tissue made up

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Ioana Dobre Transport in stems -Xylem transports water and minerals to leaf and is essentially passive Phloem = tissue made up of conducting tubes called sieve tubes - have crossed walls in them, transport sugary sap up from the leaves to any growing or non- photosynthetic tissue. It is a circulatory system - energy is derived from companion cell *huge number of mitochondria* --> the engine that enables transport The dicot stem (in class diagram) - Epidermis – waxy layer + secondary metabolites for protection - Collenchymas has fortified cell walls for protection. Provides cylindrical support - Parenchyma – relatively undifferentiated cells - Pith – extremely large cells that may collapse - Vascular bundle ( xylem, phloem and procambium) Phloem and Sugar transport - Sieve tubes have little structure except transcellular strands, crosswalls - Companion cells provide energy for sap transport through abundant mitochondria - Transport is from source ( leaves) to sink (growing or non-photosynthetic tissue) Phloem anatomy - the pressure inside the sieve tubes is very high. Hard to handle this type of tissue ( very sensitive) -no mitochondria/nucleus/chloroplasts inside the sieve tube. therefore companion cells are highly differentiated P ressure flow mechanism (in class diagram) - Companion cell “loads” sucrose from leaves by active transport into sieve tube
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This note was uploaded on 02/21/2012 for the course BIO Bio2137 taught by Professor Namroud during the Fall '11 term at University of Ottawa.

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Transport_in_stems - Ioana Dobre Transport in stems-Xylem transports water and minerals to leaf and is essentially passive Phloem = tissue made up

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