Transpiration
Overview
On a hot day a single tree can pull hundreds of litres of water up from its roots to its leaves, where most of it simply evaporates away. This loss of water vapour, transpiration, is the engine that drives water all the way up a plant, with no pump at all.
In this lesson you will learn what transpiration is, how temperature and wind speed change its rate, and how to measure it. Extended students will explain the transpiration pull that lifts water up tall trees, how leaf structure and stomata control water loss, and why a short of water makes a plant wilt.
Objectives
- Describe transpiration as the loss of water vapour from leaves
- State that water evaporates from the surfaces of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour
- Investigate and describe the effects of variation of temperature and wind speed on transpiration rate
- [Supplement] Explain how water vapour loss is related to: the large internal surface area provided by the interconnecting air spaces between mesophyll cells and the size and number of stomata
- [Supplement] Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by forces of attraction between water molecules
- [Supplement] Explain the effects on the rate of transpiration of varying the following factors: temperature, wind speed and humidity
- [Supplement] Explain how and why wilting occurs
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Lesson Evaluation
Congratulations on completing the lesson on Transpiration. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Transpiration is best defined as the: A. uptake of water by roots B. loss of water vapour from leaves C. movement of sugar in phloem D. loss of mineral ions Answer: B
- Which change increases the rate of transpiration? A. higher humidity B. lower temperature C. higher wind speed D. still air Answer: C
- Water vapour leaves the leaf mainly through the: A. xylem B. stomata C. cuticle D. phloem Answer: B
- [Supplement] The water column in the xylem does not break because of: A. active transport B. cohesion between water molecules C. lignin pumping water D. osmosis in the leaf Answer: B
- A potometer bubble moves 60 mm in 5 minutes. The rate of uptake is: A. 5 mm/min B. 12 mm/min C. 60 mm/min D. 300 mm/min Answer: B
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