Assignment

Using TranspirometersMust be put in your own word

Preparing the Plant (this can be done hours before the experiment is to be conducted):

1. Select a plant that has a section of stem that is of slightly larger diameter than the tan rubber tubing attached to the pipette tip.

2. Cut the plant off at its base, below where the diameter is slightly larger than the rubber tubing. Immerse cute end in pan of water.

3. Immerse the pipette with rubber tubing attached in the pan of water to remove all air from the pipette and tubing. This may require pinching and squeezing the tubing. All air bubbles must be removed.

4. With the stem submerged, cut the plant again at the point where the stem is slightly larger than the rubbing tubing. Keep the cut stem under water at all times.

5. Slide the rubber tubing over the cut stem.

6. Hold the plant and tubing out the water and check for leaks. If air percolates into the tip of the pipette right away then there is a leak. If there is a leak, resubmerge and try sliding the tubing onto the stem farther.

Preparing the Apparatus:

1. Flush the system by opening the screw valve below the reservoir. Flush until no bubbles leave the micropipette then clamp off the micropipette using the spring clamp. Continue flushing until no bubbles are present in the line where the plant will be inserted.

2. Insert the plant and pipette combination into the tube. Wrap a paper towel around the stem of the plant and insert the plant into the open clamp. Clamp just enough to hold the plant upright.

3. Open the spring clamp on the line leading to the micropipette.

4. Open the screw valve on the reservoir just enough for water to drip from the micropipette and then close the screw valve. Blot the drop from the tip of the pipette.

5. If the leaves of the plant are very wet, gently blot them dry.

6. Transpiration should be noticeable within a few minutes as water is drawn from the micropipette.

Measuring Transpiration Rates:

1. The micropipette is marked at the 100 μL point. Students can measure the length to the mark (usually about 88 mm) and then calculate a conversion factor (88 mm/100 μL).

Using the conversion factor they can calculate the volume transpired per unit time.

2. Factors that may affect transpiration rates are light, heat, and wind. However, exposure to extremes of heat or wind may cause the plant to close its stomates rather than transpire more. This might be something to try at the end of a lab period.