Potometer

Question 1

What is a potometer used for>

Answer 1

• measure the rate at which leafy shoots cut from plants abosrb water

Question 2

What is a common misconception about potometers?

Answer 2

• potometers measure water absorbtion and not the rate of transpiration

Question 3

How can rate of transpiration be measured?

Answer 3

• if placed on a sensitive balance they measure both water uptake (by following movement of the bubble of air) and rate of transpiration (water loss in mass)

Question 4

What are the precautions when using a potometer?

Answer 4

• leafy shoot cut under water and placed into the potometer under water
  
  • so that air does not enter the xylem vessels and block them
• the leafy shoot should be left in the potometer from some time to adjust before any readings are taken
• reading plotted on graph and the rate of uptake calculated when at least 3 ratings are on a straight line
  
  • rate is gradient
• conditions around the the leafy shoot should remain constant while reading are tkaen
  
  • repeat readings used to ensure the movement of the bublbe is consitent
• condition can be changed by altering temp, humidity, wind speed, and light intensity
  
  • while invesitgating one factor, all others hsould be kept cosntant
  • difficult in school unless you have an environmental chamber that maintains constant conditions

Question 5

How is volume of water used calculated?

Answer 5

• readings are given as distance travelled over a certain period time
• find radius of narrow tube
• volume of cylinder = πr²h