Flowering plants (transport, storage, gas exchange)

• Plant mode of nutrition

  Autotrophic
• How does water enter root hairs?

  Osmosis
• Plant metabolism


  Respiration, photosynthesis, and reactions that contribute to other processes such as cell division, elongation and reproduction
• Root hairs adaptions

  • Thin walls
  • Large surface area
  • No cuticle so water is able to enter
• Osmosis

  The movement of water form high water concentration to low water concentration across a semi permeable membrane
• The cytoplasm of root hairs is _ concentrated than the water in the soil

  More
• What is the cortex?

  The area occupied by ground tissue
• Water uptake by the roots

  1. Water enters root hairs
  2. Osmosis
  3. Movement of water across cortex into the xylem tissue
  4. Continues to diffuse until it reaches the centre of the root
• When can root pressure be weak?


   During summer
• Transpiration

  The loss of water vapour from the leaves [and other aerial parts of a plant] by evaporation
• Most transpiration takes place...

  Through openings called the stomata found on the underside of the leaf
• Adaptation of stomata

  Found on underside of the leaf
• When transpiration occurs it leaves the ground tissue less swollen and turgid →more concentrated than xylem cells
• When ground tissue is less turgid, water passes from xylem tissue to ground tissue due to an osmotic gradient (concentration difference)
• As water molecules are pulled from xylem cells by osmosis, they pull the water molecules → cohesion.

  Water is being sucked from the roots to fill the space left by the water leaving the xylem tissue
• Wilted plant

  The plant has lost more than its weight in water
• How do plants control transpiration?

  • Waxy cuticle
  • Stomata on underside of leaf {adaption}
  • Guard cells
• Guard cells


  Regulate the opening and closing of the stomata
• Cohesion tension model

  • Water evaporates from the xylem into the air space in the leaf and eventually out through the stomata
  • As transpiration pulls each water molecule out of the xylem the next is pulled with it due to their high cohesion
  • Once there is a continuous supply of water in the xylem tube this will work through the entire plant. Xylem narrow tube
  • The water molecules pulling causes the xylem to stretch, putting the water under tension
  • The cohesion ability is strong enough to withstand the pressure and this tension can pull water to a height of 150m
• • The stomata open during the day -tension causes xylem to become narrower (can see in stem)
  • Transpiration stops at night when stomata close, xylem return to original shape