Plant Biology
Environment: Water

PLANT WATER RELATIONS

 

• How do plants control their use of water under different environmental conditions?

   

• Which environmental conditions have the most effect on water usage by plants?

   

• What are the combined effects of wind speed and light on water uptake - simply additive, or more or less than we might expect from the effects of these variables separately?

  Procedure

   

  1. Collect 4 RCB (Brassica oleracea) plants of similar size.

      

  2. Wrap the containers with foil to cover base and medium.

      

  3. Label the plants 1, 2, 3, 4 and with your name.

      

  4. Weigh each plant to the nearest 0.01 g and record the weights on the table below - Wt (1).

      

  5. Put the plants in the appropriate environment and note the time you do this.

      

  6. After one hour collect your plants and weigh them again - Wt (2).

      

  Make acetate peels from each plant (see next page)

   

  1. Cut the plants at ground level and record the weight of shoot (including the leaf you used for acetate peel)

      

  2. Calculate the water loss by each plant (1-2) and divide this by the weight of shoot. Enter your data on the master table for the whole class.

  #	Conditions	Wt (1)	Wt (2)	(1-2)	Shoot	(1-2)/S
  1	light & fan
  2	shade & fan
  3	light & no fan
  4	shade & no fan

  During the hour, we will also record temperature and humidity in the different environments:

  Conditions	Temp (F)	RH (%)	# open	# closed
  Light & fan
  Shade & fan
  Light & no fan
  Shade & no fan

  Acetate peels

  In parallel with the above experiment we will try to get some data on stomatal opening under the different environmental conditions.

  Before you take the experimental plants practice this technique with a leaf from one of the extra plants.

  Detach a leaf from the plant and without delay paint the top surface with a thin layer of cellulose acetate in acetone solution.

  Dry the leaf as fast as you can - if it takes more than 15 seconds you have too much acetate - try again.

  Use your finger nail or a blade to lift the edge of the acetate from the leaf.

  When you have got it right do this with a leaf from each of your plants.

  Put each acetate peel in a bag labelled with the conditions it came from. Save the peels for the next microscope lab.

  Do not allow paint brushes to dry out with acetate mixture on them - rinse in acetone after use.

  During this lab have a look at the setups on the bench.

  Which of the physical setups resembles the plant shoot and what are the analogies between them? (what corresponds to xylem, leaf, stomata?):

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  Which setup resembles the process of water uptake by a living plant cell? Again waht are the analogies? (what corresponds to cellular membrane and vacuole?)

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  What important plant cell component is missing?

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