Topic 6: Plant Structures and Their functions

• What makes up the biomass of an orgainsm?


  Complex molecules that the plant needs to grow
• Formula needed for inverse square law


  1/d^2
• Temperature has to be just right for photosynthesis
• Not enough light slows down the rate of photosynthesis
• Too little carbon dioxide slows photosynthesis down
• Root hair cells take in minerals and water
• Phloem tubes transport food both ways
• Xylem takes water up
• Transpiration is the loss of water from the plant
• Stomata are needed for gas exchange
• Guard cells flaccid= closed

  Guard cells turgid = open
• Faster transpiration = faster water uptake
• Transpiration rate is affected by enviromental factors:

  • light intensity (more light = more transpiration)
  • temperature (warmer = faster transpiration)
  • air flow (more wind = more transpiration)
• rate of transpiration = distance moved/time taken
• Palisade layer has lots of chloroplasts
• Upper epidermis is transparent so light can pass through to palisade layer
• Waxy cuticle helps reduce water loss by evaporation
• Auxins are plant growth hormones which control growth in roots and shoots.
• Auxin is produced in the tips and diffuse backwards to stimulate cell elongation process
• Auxin promotes growth in shoots but inhibits grown in roots
• Auxins change the direction of shoot growth
• Shoots are positevely phototropic (grow towards the light)
• Shoots are negatively gravitropic (grow away from gravity)
• Auxins change the direction of root growth
• Roots are positively gravitrophic (grow towards gravity)
• Roots are negatively photographic (grow away from light)
• Plant hormones commercial uses:

  • Selective weedkillers
  • Growing from cuttings with rooting power
  • Controlling flower and fruit formation
  • Producing seedless fruit
  • Controlling the ripening of fruits
  • Controlling seed germination
• Gibberellins are a group of plant hormones responsible for growth and development.