Topic: Transpiration
Lesson 1: Introduction to Transpiration
| Section | Details |
|---|---|
| Objective | – Describe transpiration as the loss of water vapour from leaves. – Understand the process of water evaporation from mesophyll cells and diffusion through stomata. |
| Activities | Starter (5 mins): Show a time-lapse video of a plant losing water or discuss why plants lose water. Main (25 mins): 1. Define transpiration and explain its importance in plants. 2. Describe the process: – Water evaporates from mesophyll cells into air spaces. – Water vapour diffuses out of the stomata. 3. Use diagrams to illustrate water loss and the role of stomata. Plenary (10 mins): Students label a diagram of a leaf showing the path of water vapour during transpiration and write a brief explanation. |
| Resources | Leaf cross-section diagrams, videos of transpiration, worksheets for labeling diagrams. |
| Time | 40 minutes |
| Homework | Write a paragraph explaining why transpiration is necessary for plants. |
| Assessment | Students correctly label diagrams and explain the process of transpiration. |
| Past Paper Practice | IGCSE Biology 0610/21/M/J/19 Q5(a). |
Lesson 2: Factors Affecting Transpiration
| Section | Details |
|---|---|
| Objective | – Investigate and describe the effects of temperature and wind speed on the rate of transpiration. – Explain how internal leaf structure affects water vapour loss. |
| Activities | Starter (5 mins): Ask students why plants lose more water on hot or windy days. Main (25 mins): 1. Conduct an experiment to investigate transpiration rate using a potometer or by observing water loss from leaves. – Vary temperature or wind speed to observe changes in water loss. 2. Discuss the effects of factors on transpiration: – Temperature: Increases evaporation and diffusion rates. – Wind speed: Removes water vapour near stomata, increasing diffusion. 3. Explain how mesophyll air spaces and stomata size/number affect transpiration. Plenary (10 mins): Students summarize how temperature and wind speed influence transpiration. |
| Resources | Potometer, fan, heater, leaves or small plants, worksheets for experiment recording. |
| Time | 40 minutes |
| Homework | Write an explanation of how humidity affects the rate of transpiration. |
| Assessment | Students record observations during the experiment and explain their findings. |
| Past Paper Practice | IGCSE Biology 0610/31/O/N/19 Q2(b). |
Lesson 3: Mechanism of Water Movement and Wilting
| Section | Details |
|---|---|
| Objective | – Explain how water moves upwards in the xylem due to transpiration pull. – Understand the effects of temperature, wind speed, and humidity on transpiration. – Explain how and why wilting occurs. |
| Activities | Starter (5 mins): Show an animation of water moving through a plant and ask students to predict how water reaches the leaves. Main (25 mins): 1. Explain the mechanism of water movement in the xylem: – Transpiration pull draws water upwards. – Water molecules are held together by cohesion. – Adhesion helps water cling to the walls of the xylem. 2. Discuss the effects of temperature, wind speed, and humidity on transpiration rate. 3. Explain wilting as the result of excessive water loss, where cells lose turgor pressure. Plenary (10 mins): Students create a flowchart summarizing water movement in the xylem and write a short explanation of wilting. |
| Resources | Animations of water movement, diagrams of wilting plants, worksheets for creating flowcharts. |
| Time | 40 minutes |
| Homework | Research how desert plants minimize transpiration and write a brief report. |
| Assessment | Students explain the transpiration pull mechanism and describe the causes and effects of wilting. |
| Past Paper Practice | IGCSE Biology 0610/21/M/J/20 Q6(b). |
Key Notes for Teachers:
- Use practical experiments to demonstrate the effects of environmental factors on transpiration.
- Reinforce the role of internal leaf structures, such as air spaces and stomata, in water vapour loss.
- Use animations and diagrams to visualize the transpiration pull mechanism and wilting.
Key Notes for Students:
- Transpiration is the loss of water vapour from leaves through stomata.
- Environmental factors like temperature, wind speed, and humidity affect transpiration rates.
- Water moves upwards in the xylem due to transpiration pull, cohesion, and adhesion.
- Wilting occurs when water loss exceeds water uptake, causing cells to lose turgor pressure.
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