Plant Organ System (AQA GCSE Biology): Revision Note

Transport in plants

• The roots, stems and leaves are plant organs that together form an organ system for the transport of substances around the plant

• These organs are made up of specialised tissues and cells, which are adapted to carry out this transport function

  • Tissues: xylem and phloem

  • Cells: root hair cells

Transport tissues

• Plants contain two types of transport tissue:

  • xylem (pronounced: zy-lem)

  • phloem (pronounced: flow-em)

Xylem

• Xylem vessels transport water and mineral ions from the roots to the stem and leaves

• This continuous upward movement of water from the roots to the leaves, via the xylem, is known as the transpiration stream

• Features that aid xylem transport include:

  • hollow cells: the lack of internal structures allows the continuous flow of water

  • absence of end walls: this also aids continuous flow

  • cell walls strengthened by lignin: this prevents the vessels from collapsing under pressure

Phloem

• Phloem vessels transport dissolved sugars (and amino acids) either upwards or downwards

  • The direction depends on whether sugars are being produced by photosynthesis or released from storage organs

• Features that aid phloem transport include:

  • pores in the end walls: this allows movements of substances between phloem cells

  • reduced cell contents: a lack of organelles and reduced volume of cytoplasm provides more space for transport

Use this image