Bio 2.4

• Epidermis


  Protects roots as they grow through the soil
• Cortex


  Can act as a storage organ, intercellular spaces allow movement of water and ions
• Endodermis


  Has a waterproof layer that forces water and ions into the cytoplasm of the endoderm cells and controls transport into the xylem
• Pericycle


  Has a role in controlling transport into the xylem, site of lateral root growth
• Xylem


  Transports water and ions from the roots to the stem and leaves
• Phloem


  Transports the products of photosynthesis to the roots from the leaves
• Cambium


  A meristematic tissue that can undergo mitosis to produce more xylem and phloem
• Root hairs


  • Presence for the uptake of water and mineral ions
• Root hair cells


  Extensions of the root epidermal cells to increase surface area
• More surface area


  More absorption
• Water and ions


  Absorbed mainly through the root hair cells
• The images below show the external appearance of root hairs under high power and a drawing to show the structure of an individual root hair cell
• Adaptations of root hairs to increase absorption


  • Thin cellulose cell wall on root hair extension so the distance for transport is short
  • Large numbers of root hairs each with a long and thin extension into soil to increase the surface area for absorption
  • Large number of mitochondria to produce ATP for active transport of ions
• Ways water can be absorbed

  • Passively into the cell wall which acts as a sponge
  • Move into the cell cytoplasm through osmosis
• Ways ions can be absorbed

  • Passively with water into the cell wall
  • By active transport into the cell cytoplasm
• Mycorrhizae are fungal associations with roots that greatly increase surface area. As much as three meters of fungal hyphae can extend from each centimetre of root. This is an example of mutualism/symbiosis and is an ancient association; some of the oldest terrestrial plant fossils have fungal associations
• Cuticle


  • Reduces water loss through evaporation
  • Transparent to allow light to pass through for photosynthesis (in green stems)
  • Protection of the stem
  • May have hairs to deter insects/animals from eating them
• Collenchyma


  • Cell walls thickened with cellulose to strengthen the stem while remaining flexible
• Cortex parenchyma


  Can act as a storage organ
• Xylem


  Transports water and ions from the roots to the stem and leaves
• Phloem


  Transports the products of photosynthesis to the roots from the leaves
• Stem


  • Intercellular spaces allow movement of water and ions and gases
  • Thin-walled cells that act as packing tissue-often breaks down in older stems
  • Lignified cells that provide strength and support to the stem
• MacBook Air