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Transport in Plants: The Xylem | A-level Biology | OCR, AQA, Edexcel
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The key points covered of this video include:
1. Structure of the Xylem
2. Formation of Xylem
3. Adaptations of Xylem to its Function
Structure of the Xylem
Xylem vessels are dead cells stacked end-to-end. Xylem cells have no cell walls at their ends that would slow the flow of water. Xylem cells are lined with a waterproof coat made of the polysaccharide lignin. In a vascular bundle xylem vessels are continuous hollow tubes that run through the plant.
Formation of Xylem Vessels
Immature xylem vessels are waterproofed when lignin is deposited on the inside of their cell walls. This process of lignification kills the cells and allows for maximum flow of water through the hollow tubes.
Adaptations of the Xylem
There are holes in the xylem with no lignification - these are called bordered pits. The vessels are narrow enough to ensure that water travels upwards in an unbroken column. There are no end walls or organelles to impede water flow
Summary
Plants have different transport requirements for different substances
Xylem transports water and mineral ions from the roots upwards
Phloem transports assimilates up and down the plant
Xylem vessels are formed from the lignification of early xylem cells
Xylem vessels are well adapted to transporting water
Incomplete lignification
Bordered pits
Narrow vessels
No cytoplasm or cell contents
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