AQA GCSE Biology

Revision Notes

2.5.2 Plant Organ System

Transport in Plants

  • The structure of root hair cells, xylem and phloem are adapted to their functions
  • The roots, stem and leaves form a plant organ system for transport of substances around the plant

Functions of xylem & phloem

  • Plants contain two types of transport vessel – xylem and phloem
  • Xylem vessels – transport water and minerals (pronounced: zi-lem) 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 (pronounced: flow-em)
  • These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles

Vascular tissue in a dicotyledonous plant, IGCSE & GCSE Biology revision notes

Vascular tissue in a dicotyledonous plant

  • 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

Structure of the root, IGCSE & GCSE Biology revision notes

The structure of a root specifically allows it to maximise absorption of water by osmosis and mineral ions by active transport

  • 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, IGCSE & GCSE Biology revision notes

Pathway of water into and across a root


  • 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

Exam Tip

If you are asked to identify the xylem or phloem in a diagram showing a cross-section of a root, stem or leaf just remember that xylem is always on the inside and phloem is always on the outside.

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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