Name: _______________________________ Date: ___________
AP Biology Lab 11: Transpiration
Report
WHAT
Topic: transpiration in plants
Vocabulary: C 3 plants, C 4 plants, CAM plants, cuticle, guard cells, stomata, tracheids, transpiration, vessel elements, xylem
Expected results:
• Transpiration will occur at a measurable rate
• Transpiration rate will increase when plant is exposed to heat lamp
Actual results: (same -- did not do third part of lab)
Time (min)
0
3
6 water level (mL)
0.900
0.890
0.875
Time (min)
0
3
6 water level (mL)
0.900
0.880
0.862
9 0.865
9 0.843
HOW
Ideal procedure: Set up a controlled experiment to test variables that affect transpiration in plants.
• Keep most conditions constant (same test plant for all tests, same potometer)
• Vary some conditions -- the independent variables (not exposed to heat lamp, exposed to heat lamp)
• Measure one variable over time -- the dependent variable (water uptake)
Actual procedure: (same -- did not do third part of lab)
WHY
Explanation of results:
In nature water moves from the roots (intake points) to the leaves (exit points), which makes water available in the leaf cells for use in photosynthesis. Carbon dioxide enters the plant through the leaf stomata -- some water within the leaves will also exit through those same openings. Because water molecules are polar and stick to one another via hydrogen bonding, the exiting water molecules exert a “transpiration pull” on other water molecules located within the leaf/stem/roots pathway of xylem vessels. In this experiment the amount of water exiting the leaves due to transpiration can be measured using a potometer.

Name: _______________________________ Date: ___________
Explanation of process:
• Because the potometer was calibrated to the 1/100 mL, we are able to record the values to the nearest 1/1000 mL
• The potometer must not contain air bubbles -- a continuous “chain” of water molecules must be maintained
CONCLUSIONS
Big ideas:
Connections: