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Phloem Loading

OCR AS-level BiologyMass Transport in PlantsLesson 9 of 18

Active phloem loading uses the apoplast pathway and uses energy and membrane-bound co-transporter protein and a proton pump to move sucrose into the sieve tubes.

Passive phloem loading transports sucrose freely through plasmodesma in the symplast pathway.

Apoplast Pathway

Diagram

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Key terms in this lesson

ATP
Adenosine triphosphate, a nucleotide that acts as the immediate energy source of a cell, releasing energy when hydrolysed to ADP and inorganic phosphate.
diffusion
The net movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient.
facilitated diffusion
The passive movement of molecules or ions down their concentration gradient through a channel or carrier protein.
osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane.

More in Mass Transport in Plants

All 18 lessons in Mass Transport in Plants · All OCR AS-level Biology topics