Transpiration lesson

Introduction

Task

Use a potometer to measure the rate of transpiration following three environmental conditions

Formulate a hypothesis for your experiment.
Identify the following variables, i) The dependent variable, ii) the independent variable, ii) The controlled variables.
Record the results in a table
Draw a graph to show the results for the different environmental conditions
What can you conclude from the results.

Process

A potometer will be used to measure the rate of transpiration, students are required to make their potometer following these instructions.

Apparatus needed include: drinking straw, small plastic bag, a soft green leafy shoot, vaseline, play dough, a marking pen, an elastic band and a ruler

Cut the stem of the leafy shoot under water. The stem must be cut underwater to prevent air from entering the xylem vessels.
Make sure that the stem of the leafy shoot will fit tightly into the top of the straw. Remove the leafy shoot from the straw for now.
Fill in straw with water, putting your finger on one end to stop water from running out.
Put the leafy shoot into the open end of the straw. make a seal around the leafy shoot using the play dough and Vaseline.
Make sure its airtight and watertight . If it is not, all the water will run out of the straw when you take your finger off the straw
Use marking pen to mark water level in the straw.
If you have not managed to seal the end with the leafy shoot properly , place the straw on its side. This should prevent water loss from the open end.

Evaluation

Assessment criteria	Total marks
1. Potometer is well designed	5
2. hypothesis for the experiment	2
3. Identifying dependent ,independent and controlled variables	4
4.Recording results in a table	4
5. Drawing graph illustrating results for the different environmental conditions .	4
conclusion from the results.	1

Total: 20 marks

Conclusion

After completing this lesson ,learners will be able to

Credits

F. clitheore et al.2014. Focus Life sciences learners book grade 10. pp 101-103.

Teacher Page

Notes

Transpiration is the evaporation of water from leaves of plants.

Factors affecting the rate of transpiration

Temperature: The higher the temperature, the higher the rate of evaporation. This means that high temperatures increases the rate of transpiration

Humidity: Low humidity increases the rate of transpiration and high humidity reduces the rate of transpiration.

Light intensity : Transpiration increases when there is high light intensity

Air movement: The rate of transpiration increases when the wind blows.https://www.youtube.com/watch?v=SamVxoO3BgA