1. Copy down the diagram, what do you think might be written on the end of the lines?

3. Objectives Define transpiration Explain how water is carried by the transpiration stream including structure of xylem vessels, transpiration pull, adhesion, cohesion, evaporation. State that guard cells can regulate transpiration by opening and closing stomata State that abscisic acid causes this. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

4. Task Define transpiration. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration. The movement of water from roots to the leaves due to the loss of water vapour from the leaves and stems of plants.

5. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

6. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

7. But why does it happen? Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

8. But why does it happen? Key terms: transpiration, evaporation, cohesion, vapour.

9. The transpiration stream occurs in xylem vessels and the movement of water is passive. Mature xylem vessels are long dead structures made up of cells arranged from end to end. The cell walls between the adjacent xylem cells are broken down and the cytoplasmic content dies to form a continuous tube. The cells also lack a plasma membrane which allows water to enter the vessels freely. In addition, they also contain pores in the outer cell walls which allows the movement of water out of the vessels and into the surrounding cells of leaves. The outer cell walls contain thickenings which resemble spirals or rings impregnated with lignin which makes the vessels strong and able to withstand low pressures. Low pressure (suction) is created in the xylem vessels when water is pulled out of the transpiration stream via evaporation of water vapour from the spongy mesophyll cell walls in the leaves. Heat from the environment is necessary as it provides the energy required for the evaporation of water.

10. Key terms: transpiration, evaporation, cohesion, vapour.

11. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration. Water molecules have dipoles which cause an attraction between them. Water is ‘pulled’ up the xylem vessels by transpiration. When this happens, the pull is transmitted all the way down the water column, pulling all of the water molecules up the vessel. For this to work, the xylem vessel must be a continuous column of water i.e. contain no bubbles.

12. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration. Mass flow of water in xylem vessels – pressure lowered as water leaves vessels. Water moves up from the roots where the pressure is higher. Diffusion of water through cells from xylem. Water vapour diffuses through leaf air spaces. If the concentration of water vapour in the leaf is higher than outside, water vapour will diffuse out of the leaf through the stomata. Capillary action (water molecules attracted to polar molecules in xylem walls (adhesion)). Cohesion – tension theory.

13. Explain using diagrams and written explanation the process of transpiration in angiosperms. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

14. So how is water loss reduced? Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

15. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration. Stomata can be closed to prevent water loss. Guard cells curve apart when turgid. When flaccid, the edges of the cells lie close together. However, this drastically slows transpiration and means that no carbon dioxide can enter the leaf (= no photosynthesis).

16. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration. The plant hormone abscisic acid causes the closing of stomata.

17. Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.

18. Key terms: transpiration, evaporation, cohesion, vapour.

19. Set up a potometer Key terms: transpiration, evaporation, cohesion, vapour. Outcomes 3: Describe transpiration as a process. 5: Explain the process of transpiration in plants. 7: Analyse methods which plants use in order to control transpiration.