Xylem

• What are the two main functions of xylem in a plant?

  1. Support

  2. Transport of water and mineral ions
• What is a feature of most cells found in the xylem?

  Most are dead when functioning in the plant
• What determines the rigidity of the xylem?

  The shape of the lignin- some shapes give more support than others
• What is the main part of xylem and what is its structure?

  Xylem vessels, which are made up of long tubes of dead cells with no cytoplasm or end cell walls, thick, lignified walls and lots of unlignified 'bordered pits' in the walls for the movement of water
• What are the two main tissues associated with xylem vessels in dicots?

  1. Xylem parenchyma

  2. Xylem fibers
• If lignin is the 2nd most common natural polysaccharide, then what is the first?

  Cellulose
• What is tannin and what is its purpose?

  A bitter, astringent-tasting chemical which protects plant tissue from attack by herbivores
• What is xylem parenchyma and where is it found?

  Thick-walled cells packed around the xylem vessels which store food and tannin deposits
• What are xylem fibres?

  Long cells with lignified secondary walls which provide additional strength, but do not carry water
• How is lignin laid down in xylem vessels' walls?

  Can be a number of ways- rings, spirals or even relatively solid tubes with lots of small unlignified areas called bordered pits