Transpiration

• Factor affecting the rate of transpiration

  -Humidity -Temperature-Wind speed of air movement -Light intensity
• Why the potometer does not truly measure the rate of transpiration

  -Maintain turgidity -Use water for photosynthesis -Produce water in respiration -Apparatus is not sealed
• Precautions when setting up the potometer

  -Dry the leaves-Sample under water -Cut shoot under water -Shut the tap -Ensure the apparatus is airtight and watertight
• Reservoir of water

  To return bubble to the start for repitition
• Leave the end of the capillary tube out of the water


  until an air bubble forms. Then put the end into a beaker of water
• Remove apparatus from water and DRY the leaves

  water on the leaves may make the air around the leaf more humid and reduce transpiration rate
• Assemble the potometer under the water and insert the shoot with the apparatus still under the water

  no air can enter. The apparatus is water and air tight
• Cut it at a slant


  to increase SA available for water uptake
• Cut a shoot underwater


  to prevent air from entering the xylem
• Where is the most common sink?

  Roots/meristematic tissue
• Where is the most common source?

  Leaves
• What causes mass flow to occur?

  Hydrostatic pressure in the source
• How does sap move from source to sink?

  Mass flow
• How are protons moved into the sieve tube during translocation?

  Active transport
• What is the name given to plants which are adapted to living in wet environments?

  Hydrophytes
• What is the name given to plants which are adapted to living in dry environments?

  Xerophytes
• Plants have a waxy cuticle, stomata on the underside of the leaf and lose their leaves in autumn for what purpose?

  Reduce water loss
• What is the name given to the movement of water up a xylem due to it's thin lumen?

  Capillary action
• What does the active loading of mineral ions into the xylem effect?

  Root pressure
• What stops the apoplast pathway in the cortex of the root?

  Casparian strip
• Increasing humidity


  Decreases rate of transpiration
• Increasing light intensity, wind speed, temperature and water availability

  Increases rate of transpiration
• What is transpiration?

  The loss of water vapour through the stomata of leaves.
• What is the name given to the pathway where water diffuses between cell vacuoles?

  Vacuolar
• What is the name given to the pathway where water diffuses between cell cytoplasms?

  Symplast
• What is the name given to the pathway where water diffuses between cell walls?

  Apoplast
• What is the name given to the gaps/junctions between cytoplasms?

  Plasmodesmata
• What is an important adaptation of cellulose cell walls?

  They are fully permeable to water
• How do companion cells produce a lot of ATP?

  They have a lot of mitochondria
• Why is it useful that phloem cells contain no nucleus and very little cytoplasm?

  It allows mass flow of sap to occur
• What is the importance of the growing pattern of xylem (i.e spiral, annular or reticular)?

  It allows the xylem to bend without breaking
• Why are bordered pits in the xylem important?

  They allow water to move from xylem to xylem
• What are the gaps in the lignin known as?

  Bordered pits
• Before xylem is killed and lignified, what is it known as?

  Proto-xylem
• What is the name given to the undifferentiated groups of meristematic cells in between phloem and xylem in the stem?

  Cambium
• What are the two types of specialised tissues that provide support to the leaf and stem?

  Sclerenchyma and collenchyma
• In the stem, where is the xylem located in the vascular bundle


  Towards the inside
• Where is the xylem located in the root of a dicotyledonous plant?

  The outer edge
• Which part of the vascular bundle does water travel along?

  Xylem
• What is the process of transporting sap from source to sink known as?

  Translocation