Transpiration

• What is transpiration 


  Loss of water through plant by evaporation + diffusion
• Why do plants need water

  • Reactant for photosynthesis
  • Supports leaves + shoots by keeping cells rigid
  • Cools leaves by evaporation
  • Transports dissolved minerals around plant
• How do plants absorb water and minerals

  Root hair cells
• What do the 'hairs' on the surface of roots do?


  Gives plant large surface area for absorbing water and mineral ions from soil
• What is the process called when absorbing water 


  Osmosis
• What is osmosis 


  Movement of water from a dilute to concentrated solution through a partially permeable membrane
• What is the process called when absorbing mineral ions 


  Active transport
• What is active transport 


  Movement of particles from an area of low- -> high concentration against a concentration gradient (needs energy)
• What is the role of the xylem 


  Transport water = mineral ions form roots->leaves
• How are xylem vessels adapted for their role 


  -Made of dead cells

  -Continuous column of water

  -No end walls (to not disrupt the flow)

  -Walles thickened with lignin
• What are stomata 


  Tiny pores that allow CO2 + O2 to diffuse in and out
• Where are stomata found


  Lower surface of the leaf
• What other gas does stomata allow to diffuse out 


  Water Vapour
• What surrounds the stomata 


  Guard cells
• What are the guard cell's role

  Change shape -> control size of the pore (changes shape depending on amount of water within them)
• How do you describe the guard cells when they have a sufficient amount of water 


  Turgid (swollen with water)
• What happens to the stomata when the guard cells are turgid 


  They're open
• How do you describe the guard cells when they have have a low amount of water 


  Flaccid
• What happens to the stomata when the guard cells are flaccid 


  Closed
• How can the guard cells be turgid


  Due to osmosis water moves into the cells
• What causes transpiration 


  Evaporation and diffusion of water from plants leaves
• Describe the transpiration stream


  • Water evaporates + diffuses by osmosis through stomata
  • Loss of water creates shortage of water in leaf
  • Leads to more water being drawn up xylem
  • More water drawn up from roots ->constant stream of transpiration
• Describe how mineral ions are transported from roots to the leaves 


  Mineral ions dissolve in water + use active transport + then through the xylem + diffusion
• What are the 3 facts affecting rate of transpiration 


  • Light intensity
  • Temperature
  • Air flow
• How does light intensity affect rate of transpiration 


  • Brighter the light -> greater rate of transpiration
  • In dark, stomata closes
  • Photosynthesis cant happen in the dark
  • So little water can escape
• How does temperature affect rate of transpiration 


  • Warmer temp -> faster transpiration rate
  • Water particles have more energy so can evaporate + diffuse out of stomata
• How does air flow affect rate of transpiration 


  • Better air flow -> faster transpiration rate
  • So water vapour has diffused out + swept away
  • Water concentration low in air surrounding leaf
  • If no air flow -> water vapour would surround leaf and won't be able to diffuse out due to no concentration gradient
• What can you use to estimate the rate of transpiration

  Potometer
• What is the role of the potometer 


  Measures water uptake which is = to rate of transpiration
• Describe the practical to estimate rate of transpiration


  • Record apparatus as shown
  • Record start position of air bubble
  • Start stopwatch + record distance it moved in a specified amount of time
  • Calculate speed (s=d/t)