Plant Organ System (AQA GCSE Biology): Revision Note

Transport in plants

Plant organs

• The structure of root hair cells, xylem and phloem are adapted to their functions

Functions of xylem and phloem

• Plants contain two types of transport vessels:

  • xylem (pronounced: zi-lem)

  • phloem (pronounced: flow-em)

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

  • It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream

• Phloem vessels transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem

• These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles

Vascular tissue in a dicotyledonous plant

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• Root hair cells are adapted for the efficient uptake of water by osmosis and mineral ions by active transport

  • Root hairs are single-celled extensions of epidermis cells in the root which increase the surface area of the cells significantly; this increases the rate of the absorption of water by osmosis and mineral ions by active transport

  • They grow between soil particles and absorb water and minerals from the soil

  • Water enters the root hair cells by osmosis

  • This happens because soil water has a higher water potential than the cytoplasm of the root hair cell

Levels of structure in plant roots

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• Osmosis causes water to pass into the root hair cells, through the root cortex and into the xylem vessels:

Pathway of water into and across a root

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• Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells

• The pathway is:

root hair cell → root cortex cells → xylem → leaf mesophyll cells