OCR Biology A

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Xylem vessels are very long, hollow structures formed from cells (vessel elements) joined end to end.

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The cells have no end walls which forms a continuous hollow column.

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The cells are dead and contain no cytoplasm and no nuclei.

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Xylem has two main functions: 1. Transport water and mineral ions from the roots to the shoots and leaves 2. To provide support

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Xylem parenchyma are thick-walled cells which pack around xylem vessels, storing food and containing tannin deposits. Tannin is a bitter-tasting chemical that protects plant tissues from attack by herbivores.

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Xylem have lignified walls which helps support walls, stopping them from collapsing inwards. Lignin can be laid in the walls as rings or spirals, which allows flexibility and prevents the stem breaking.

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Xylem have small unlignified areas called bordered pits. This is where water leaves the xylem and moves into other cells.