Plant Transpiration Lab[1]

Water is transported in plants, from the roots to the leaves, following a decreasing water potential gradient. Transpiration, or loss of water from the leaves, helps to create a lower osmotic potential in the leaf. The resulting transpirational pull is responsible for the movement of water from the xylem to the mesophyll cells into the air spaces in the leaves. The rate of evaporation of water from the air spaces of the leaf to the outside air depends on the water potential gradient between the leaf and the outside air.

                        

Various environmental factors, including those conditions which directly influence the opening and closing of the stomata, will affect a plant’s transpiration rate. This experiment will measure transpiration rates under different conditions of light, humidity, temperature, and air movement. The data will be collected by measuring pressure changes as the plant takes up water into the stem.

                

OBJECTIVES:

PROCEDURE

Part A: Testing the Control

  1. Here is a video explaining the following set-up to test rates of transpiration.
  1. Investigate Transpiration with Gas Pressure Sensor

  1. Position the ring stand, utility clamps, and Gas Pressure Sensor as shown in Figure 1.

  1. Prepare the plastic tubing.                                        
  1. Connect the plastic syringe to one end of a 36–42 cm piece of plastic tubing.
  2. Place the other end of the tubing into water and use the syringe to draw water up into the tubing until it is full. Tap the tubing to expel any air bubbles that form inside the tube.
  3. Slip a plastic tubing clamp onto the tubing as shown in Figure 2.
  4. Bend the tubing into a U shape with both ends up. Remove the syringe, leaving the tubing full of water.

  1. Select a plant that has a stem roughly the same diameter as the opening of the plastic tubing. Using a scalpel or razor blade, carefully cut the plant one inch above the soil. Place the plant under water against a hard surface and make a new cut at a 45° angle near the base of the stem.

  1. Connect the plant to the tubing.
  1. The plastic tubing has a white plastic connector at one end that allows you to connect it to the valve on the Gas Pressure Sensor. Raise the end of the tubing with the connector until you see water beginning to drip out of the other end.
  2. Carefully push the cut stem of the plant down into the end of the tubing where the water is dripping out. Be careful not to allow any air bubbles to form between the cut portion of the stem and the water in the tube.
  3. Push the plant down as far as it will go without damaging the plant. At least one centimeter of the plant stem should fit into the tubing. If the stem is too large for the tubing, cut the stem at a higher point where it is smaller.
  4. Squeeze the tubing clamp shut as tight as possible as shown in Figure 3.

  1. When the tubing clamp is shut tight, invert your plant cutting to check for any leaks. If water does leak out, turn the plant right side up and try tightening the clamp further.

Important: Be sure the tubing is filled completely with water. The water column must be flush with the stem. There should be no air visible at the base of the stem. If water moves down the tube away from the stem after it has been inserted, check for a leak in the system.

  1. Connect the plastic tubing to the sensor valve. Caution: Do not allow water to enter the valve of the Gas Pressure Sensor.

  1. Secure the plant in an upright position with the utility clamps as shown in Figure 1. It should be positioned so that the cut stem is about 8 cm below the water level at the other end of the tubing, as shown in Figure 1.

  1. Place a mark on the tube at the starting water level to allow you to refill the tube to the proper level in Step 17.

  1. Place your plant setup in an area where the wind, humidity, and temperature are reasonably constant. This will be your control setup.

  1. Allow the system 5 minutes to adjust to the environment. While the system is adjusting, set up the computer.

  1. Connect the Gas Pressure Sensor to the computer interface. Prepare the computer for data collection by opening the file “10 Transpiration” from the Biology with Vernier folder of Logger Pro.

  1. Check the base of the plant stem in the water tube to make sure that no air bubbles or air pockets have formed that will prevent the plant from taking up water. If an air pocket has formed, refit the plant in the tubing before initiating data collection in Step 13.

  1. After the plant has equilibrated for 5 minutes, click to begin data collection. Data will be collected for 15 minutes.

  1. When data collection has finished, find the rate of transpiration for your plant. To do this:
  1. Move the mouse pointer to the point where the pressure values begin to decrease. Click the mouse button and drag the pointer to the end of the data, then release the mouse button.
  2. Click the Linear Fit button to perform a linear regression. A floating box will appear with the formula for a best fit line.
  3. Record the slope of the line, m, in Table 1 as the rate of transpiration for the control. Close the floating box.

  1. Calculate the surface area of all the leaves using the steps listed below in Data Processing in the data processing section.

Part B: Testing a Variable

Complete the same procedure as outlined above, but simulate one of the following environmental factors:

You do not need to create a new procedure as the process will be essentially the same, however you do need to complete the following:

You must have the previous information and experimental procedure checked before conducting your analysis.  Record your data in Table 1.

You will need to conduct two trials of your variable in order to determine an average and standard deviation.

Presentation:

Each group will present their variable condition research question and results.  A template for a presentation slide show can be found here and will be limited to no more than 5 minutes per group.

DATA PROCESSING

  1. Determine the surface area of all the leaves on your plant cutting by the following method:
  1. Cut all the leaves (not stems) off your plant and determine their mass using a balance.
  2. Estimate the total leaf surface area in cm2 for your plant by cutting out a section of leaf 5 cm × 5 cm.
  3. Determine the mass for this leaf section and divide by 25 cm2 to find the mass of one cm2 of leaf.
  4. Divide the total mass of the leaves by the mass of one cm2 to find the total leaf surface area.
  5. Record the calculated surface area in Table 1.

  1. Calculate the rate of transpiration/surface area:
  1. Divide the rate of transpiration by the surface area for each plant. These rate values can be expressed as kPa/min/cm2. Record the rate/area in Table 1.

  1. Record this value in Table 1 and submit to this Google Form.

  1. Subtract the control (rate/area) value from the experimental value. Record this adjusted rate in the last column of Table 1.   This value is an indicator of the difference between the general rate of transpiration in the species and the variable you influenced, meaning this value indicates the degree of change from the control to the variable.

  1. Record the adjusted rate for your experimental test on the board to share with the class. Record the class results in Table 2 for each of the environmental conditions tested. If a condition was tested by more than one group, take the average of the values and record in Table 2.

  1. Make a bar graph that shows the effect of your environmental condition on the transpiration of water in plant cuttings in comparison to the class average control using the class average found here.  (We do not use an x-y scatter plot graph in this case because the independent variables are not numerical values and rather simply categories.  A more appropriate extension of this experiment would be a range of your particular variable which would provide data necessary for a x-y scatter plot.) Plot the rate/area (not adjusted) for your variable test and the control on the y-axis and the test label on the x-axis.  This graph should include error bars and is Graph 1.  Upload this graph below here:

  1. Determine if there is a statistical difference between the control and your experimental value (since there is a different number of trials between the control and experimental variable, use a degree of freedom of 2):

                                

Table 1. Rate and adjusted rate of transpiration for control & experimental variable.

Test

Slope (kPa/min)

Surface Area (cm2)

Rate/Area (kPa/min/cm2)

Adjusted Rate

(kPa/min/cm2)

Control (Your Data)

(turn in this value)

Control (Class Average)

Variable Trial 1

Variable Trial 2

Average of Variable Tests

Table 2. Experimental variable adjust rate of transpiration.

Experimental Variable

Adjusted Rate

(kPa/min/cm2)

1.

2.

3.

EVALUATION:

Write an evaluation of your data and results comparing Part A & B.

EXPLORATION

TuHS Mark

IB Mark

The topic of the investigation is identified and research question is:

Background information provided for the investigation is:

Appropriateness of the methodology of the investigation.

Consideration of factors that may influence the relevance reliability and sufficiency of collected data.

Evidence of awareness of the significant safety, ethical or environmental issues

Exceeds

5-6

Relevant and fully focused.

Entirely appropriate and relevant and enhances the understanding of the context of the investigation.

Highly

Nearly all factors considered.

Full - all potential hazards identified and dealt with appropriately

Meets

3-4

Relevant but not fully focused.

Mainly appropriate and relevant and aids the understanding of the context of the investigation.

Mainly

Some factors considered.

Limited

Nearly Meets

1-2

Some relevance but not focused.

Superficial or of limited relevance and does not aid the understanding of the context of the investigation

Limited

Few factors considered.

Some

Beginni-ng

0

Standard not reached

Standard not reached

Standard not reached

Standard not reached

Standard not reached

ANALYSIS

TuHS Mark

IB Mark

Raw data is:

Data processing:

Impact of uncertainties:

Interpretation of processed data:

Exceeds

5-6

Sufficient. Could support a detailed and valid conclusion.

Appropriate and sufficient accuracy enables a conclusion to the RQ to be drawn that is fully consistent with data.

Full and appropriate consideration.

Correct valid and detailed interpretation.

Meets

3-4

Relevant but incomplete. Could support a simple or partially valid conclusion.

Appropriate and sufficient. Could lead to a broadly valid conclusion but significant inaccuracies and inconsistencies in the processing.

Some consideration.

Broadly valid limited interpretation.

Nearly Meets

1-2

Insufficient to support a valid conclusion.

Basic, inaccurate or too insufficient to lead to a valid conclusion

Little consideration.

Incorrect or insufficient invalid or very incomplete

Beginning

0

Standard not reached.

Standard not reached.

Standard not reached.

Standard not reached.

EVALUATION

TuHS Mark

IB Mark

Conclusion comparison to research question:

Conclusion comparison to accepted scientific context:

Strengths & weaknesses of investigation:

Improvements & extension of investigation:

Exceeds

5-6

Described and justified in detail.  Entirely relevant to research question and fully supported by data

Described and justified in detailed comparison to accepted scientific context

Strengths, weaknesses (limitations of the data and sources of error) discussed and provided evidence of clear awareness of methodological (procedure) issues influencing conclusion

Discussion of realistic and relevant suggestions

Meets

3-4

Described and relevant to research equation and supported by data

Described and makes some relevant comparison to accepted scientific context

Strengths, weaknesses (limitations of the data and sources of error) described and provided evidence of some awareness of methodological (procedure) issues influencing conclusion

Description of some realistic and relevant suggestions

Nearly Meets

1-2

Outlined and/or not relevant to research question or not supported by data.

Superficial comparison to accepted scientific context

Strengths, weaknesses (limitations of the data and sources of error) outlined but only account for practical issues faced

Outline of very few realistic and relevant suggestions

Beginning

0

Standard not reached.

Standard not reached.

Standard not reached.

Standard not reached.

COMMUNICATION

TuHS Mark

IB Mark

Report Presentation:

Report Structure:

Report Relevancy & Conciseness:

Report Language:

Meets

5-6

Clear; no errors hamper understanding of focus, process and outcomes

Well structured and clear; necessary information is present and presented in coherent way

Facilitates a ready understanding of the focus, process and outcomes

Subject-specific terminology and conventions is appropriate and correct

Nearly Meets

3-4

Unclear; difficult to understand the focus, process and outcomes

Not well structured and/or unclear; necessary information is missing or presented in incoherent or disorganized way

Irrelevant or inappropriate information obscures understanding of focus, process and outcomes

Many errors in subject-specific terminology and conventions

Beginning

1-2

Standard not reached.

Standard not reached.

Standard not reached.

Standard not reached.


[1] Lab adapted and modified from Vernier Software & Technology Transpiration Lab