9700 · 7.1
Structure of transport tissues flashcards
Revision flashcards for Cambridge 9700 Structure of transport tissues (syllabus 7.1). Flip, recall, then mark a real past-paper question.
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Main function of xylem?
Transport of water and mineral ions from roots to leaves; also provides structural support via lignin.
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Why are xylem cells dead?
No cytoplasm or organelles in the lumen minimises resistance to mass flow of water.
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Role of lignin in xylem?
Waterproofs walls, prevents collapse under tension, and strengthens stems.
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What are sieve plates?
Perforated end walls between sieve tube elements allowing flow of phloem sap.
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Role of companion cells?
Provide ATP and proteins for loading/unloading sucrose into sieve tubes via plasmodesmata.
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What is translocation?
Mass flow of organic solutes (mainly sucrose) through phloem from source to sink.
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What are pits in xylem?
Non-lignified regions allowing lateral water movement between vessels.
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Xylem vs phloem transport direction?
Xylem: unidirectional (upward). Phloem: bidirectional depending on source and sink.