Chapter 9 - Transport in Plants

Need for plant transport systems

• meet metabolic demands

  • internal parts don’t photosynthesise so need oxygen and glucose transported to them

  • waste products need to be removed

  • mineral ions need to move from roots

• size

  • some plants are very large

  • need to transport substances up and down

• surface area : volume ratio

  • leaves have a high SA:V but stems/trunks etc are complex and big

  • can’t rely on diffusion

Dicotyledonous plants

• have a series of transport vessels - vascular system

• xylem and phloem

• arranged in vascular bundles

Stem

Root

Dicot leaf

Xylem

• non-living

• transports water and mineral ions

• support

• flow is one way - roots → shoots

• columns of cells fused at the end

• thick lignified walls

• non-lignified pit - water leaves xylem

• no end walls

• rings, spirals or tubes of lignin running around the lumen

• surrounded by xylem parenchyma

Phloem

• living tissue

• transports food

• up and down

• sieve tube elements

• non-lignified walls

• walls are perforated to form sieve plates between cells

• have companion cells attached

  • linked to sieve tube elements by plasmodesmata (microscopic channels through the cellulose cell walls)