CATCHING H2O (TRANSPIRATION)

KEY CONCEPTS

  1. Water released into the atmosphere through the leaves of plants is called transpiration. It involves the evaporation of water from the leaves.
  2. Structures called "stomates" regulate the transpiration rate and are found on the underside of leaves.
  3. The amount of water released by a plant through transpiration is dependent upon the amount of heat in the environment, the plants need to release water, the species of the plant, and the adaptations the plant has made for water availability.
 

MATERIALS

  • 2 jars with lids
  • several leaves from a broadleaf plant
  • field journal
 
 

PROCEDURE

  
 
 

Activity

  1. Make sure the jars are clean and dry.
  2. Place the leaves into one of the jars.
  3. Cap the jar tightly.
  4. Cap the empty jar tightly. This jar serves as the control.
  5. Place the jars outside or inside under a grow light or incandescent lamp.
  6. After 15-30 minutes, make observations of the two jars. Note the differences in appearance and record in journal.
 
 

Footnote

  • Additionally, students may determine the amount of moisture from the inside of the jar (condensation) by pre-weighing a small, dry sponge and collecting the moisture from the inside of the jar that contains the leaves. The difference in weight represents the amount of water transpired by the leaves. Have students repeat the activity using leaves from different plants. Have them compare the transpiration potential for each and relate the data to the natural environment from which the plant originated.
  
 

Assessment Ideas

  • Students can be assessed by comparison of data within groups and checking for consistency in water volumes.
  • Journals and graphs can be assigned for analysis of data and checking for understanding.
  
 
 

CROSS-CURRICULAR IDEAS

  • Mathematics: Graph the results of the experiment.
  • English/Language Arts: Have the students maintain a journal.
 
 

VOCABULARY

  • condensation: the conversion of water vapor into liquid.
  • evaporation: the conversion of a liquid into a vapor due to outside heat.
  • stomates: structures on the surface of a leaf that regulate the volume of water that is released by the plant.
  • transpiration: to give off water from the leaves of plants.
  
 

SOURCE

  • "Winds of Change" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory