Plant Experiments

• What device is used to measure transpiration?

  potometer
• Can the air bubble move to the right in a potometer?

  No, only to the left
• The movement of water up the length of the xylem can be modelled using capillary tubing, filter or blotting paper and porous pots
• A potometer is a device that is used to estimate transpiration rates by measuring the rate of water loss/uptake  
• When a plant is affixed to the potometer, transpiration can be indirectly identified by the movement of water towards the plant
• Water movement in a potometer can be assessed as a change in meniscus level or by the movement of an air bubble towards the plant
• Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action)
• Capillary action is is due to a combination of surface tension (cohesive forces) and adhesion with the walls of the tube surface
• The thinner the tube or the less dense the fluid, the higher the liquid will rise during capilliary action
• Filter paper (or blotting paper) will absorb water due to both adhesive and cohesive properties
• The movement of water up filter paper is comparable to the movement of water up a xylem
• Porous pots are semi-permeable containers that allow for the free passage of certain small materials through pores
• The loss of water from the pot is similar to the evaporative water loss that occurs in the leaves of plants
• When measuring transpiration rates with a potometer, it is important to remember that not all water is lost to transpiration
• Water is also lost in what other methods?

  ~2% is used in photosynthesis and to maintain viable turgidity
• Potometers can be used to test variables that may affect the rate of transpiration in plants like: temperature, humidity, light intensity and wind exposure
• What effect does an increase in temperature have on the rate of transpiration?

  increase in the rate of transpiration
• What effect does an increase in humidity have on the rate of transpiration

  decrease in the rate of transpiration
• What effect does an increase in light intesity have on the rate of transpiration?

  increase in the rate of transpiration
• What effect does an increase in wind exposure have on the rate of transpiration?

  increase in the rate of transpiration