Transport of water

• The plant root:

  • The roots, stem and leaves form a plant organ system for the transport of substances around the plant.
  • Plant roots are adapted to maximise absorption of water and mineral ions from the surrounding soil.
  • Many epidermal cells in the root have 'hair-like' extensions that project into the soil.
  • Roots contain millions of these 'hairs' to increase the surface area for absorption.
• The structure of a root specifically allows it to maximise absorption of water by osmosis and mineral ions by active transport:

  
• Root hair cells (part 1):

  • 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.
  • They are long and thin so they can penetrate between soil particles and absorb water and minerals from the soil.
  • Root hairs increase the surface area to volume ratio which increases the uptake of water and mineral ions.
• Root hair cells (part 2):

  • The high proportion of dissolved minerals and sugars in the cytoplasm (of the root hair cell) gives it a low water potential.
  • As soil water has a higher water potential than the cytoplasm, water moves into the root hair cell by osmosis.
  • Mineral ions move into the root hair cells by active transport as the concentration of mineral ions in the soil is usually much lower than in the root hair cells.
  • They need to move into the cell against the concentration gradient which requires energy.
• A root hair cell: