Activity 7: For You To Do

6.–7. Students’ answers will vary, depending on the size of the leaf used.

8. a) The factors that might affect the results of this experiment and their effects are:

• The number of leaves in the branch. The more leaves there are, the more water is lost through transpiration.
• The kind of plant used. Some plants lose more water through their leaves compared to other plants.
• The “freshness” of the plant. The fresher the plant, the more transpiration occurs.
• The humidity in the classroom. The lower the humidity, the more water is lost by transpiration.
• The temperature in the classroom. The higher the temperature, the more water is lost by the leaves.
• The presence of a light source in the classroom. The more intense the light is, the more water is lost through transpiration.
• The “fit” of the branch on the plastic tubing. A “fit” that is not airtight will result in a lower amount of transpired water.
• The “fit” of the pipette on the plastic tubing. A “fit” that is not airtight will result in a lower amount of transpired water.

b) To reduce errors:

• Have an airtight “fit” between the plastic tubing and the pipette/branch; a paraffin wax can be used.
• Only fresh branches should be used.
• The experiment should be done near a window to have a light source or close to an artificial light source like a fluorescent bulb.

• If the factor is light, the hypothesis may state that if the plant is exposed to light then the rate of transpiration is high. The control will have light and the experimental side will not.
• If the factor is temperature, the hypothesis may state that if the plant is exposed to high temperature, then there will be a higher rate of transpiration. The control will have normal room temperature and the experimental side will have higher or lower temperature.

Teaching Tips

Using Blackline Master Ecology 7.5: Area of the Leaf Surfaces, point out to the students that they have to make approximations of those squares that are not fully within the tracing. Discuss the units of measurement to be used.

Using Blackline Master Ecology 7.6: Rate of Transpiration, discuss that this graph shows the amount of water lost per square centimeter over time. Have the students figure out what they will put/plot on the x-axis and the y-axis. You can explain that the indicator of water loss is put/plotted on the y-axis. The indicator is also known as the dependent variable. The time that elapsed independent variable is on the x-axis and the dependent variable is plotted on the y-axis.