Everything Life Sciences Grade 10

1. Cut the stem of the leafy shoot (at an angle to increase the surface area)under water
   . The reason we cut it under water is to prevent air bubbles entering the xylem vessel.
   You must use a very sharp knife or new scalpel and cut at an angle in order to increase
   surface area for water uptake in the xylem. Florists who cut plants before immersing
   them in water follow the same procedure for this reason.


2. Test to make sure the stem of the leafy twig will fit snugly into the top of the straw.


3. Remove the leafy shoot from the straw and set aside.


4. Fill the straw with water. Place your finger over one end of the straw to stop the water
   from running out.


5. Put the leafy shoot into the open end and seal it with play dough/ putti/ prestick while
   removing it from water KEEPING YOUR FINGER ON THE STRAW! Perform the fol-
   lowing steps above water.


6. Seal with Vaseline. Make sure it is air tight and water tight. If not, all the water will
   run out when you take your finger off the straw.


7. Mark the water level on the straw.


8. Place your potometer under one of the following conditions for one hour:
   
   
   • as is, in a warm, sunny place (no wind);
   
   
   • as is, in a warm, windy place;
   
   
   • with a plastic bag tied around the leaf, in a warm, sunny place; or
   
   
   • a shady place.
   
   
   
   


9. Every 10 minutes use a marking pen to mark the change in water level on the straw.
   Continue taking measurements for 1 hour.


10. Measure the distance the water moves during each time interval.

Results:

• Draw a table and record the class’ results.


• Plot a bar graph to compare the distances the water moved in the different straws.


• The class should be divided into four groups, with each group investigating the effect
  of a different condition on transpiration. At the end of the experiments, all students
  must plot the following graphs:
  
  
  • the effect of temperature on the rate of transpiration;
  
  
  • the effect of light intensity on the rate of transpiration;
  
  
  • the effect of relative humidity on the rate of transpiration; and
  
  
  • the effect of wind on the rate of transpiration.
  
  
  
  

Observations:

Record your observation from the table and bar graph.

Conclusions:

• What can you conclude from this investigation?


• Give two ways in which you can improve your experimental results.

Questions:

174 6.3. Transpiration