1. Higher Biology Adaptation Part 3

2. 2 Adaptation 3 By the end of this lesson you should be able to:  Understand what is meant by transpiration and transpiration stream.  Describe the movement of water from the soil to the leaves and into the air.  Understand how adhesion and cohesion are involved in transporting water.  Describe the uptake and transport of nutrient ions.  Explain the cooling effect of transpiration.  Explain stomatal mechanism.  Explain how different factors can affect transpiration.

3. 3 Transpiration  Transpiration is the evaporation of water from the leaves of plants, mainly through the stomata. Why is it important?  Transpiration supplies water and nutrient ions to all parts of the plant.

4. 4 Transpiration Stream  The Transpiration Stream is an unbroken column of water from the roots through the xylem, to the leaves and finally evaporation to the atmosphere.

5. 5

6. 6 Water’s journey 1. From the soil into the root hair The root epidermis is permeable and the root hair provides a large surface area for the absorption of water. Water crosses into the cells by osmosis.

7. 7 Water’s journey 2. From the root hair into the cortex Water crosses along a concentration gradient by osmosis.

8. 8 Water’s journey 3. From the cortex to the xylem Water travels along a concentration gradient, From cell to cell by osmosis Or, Along water filled spaces between cell walls by diffusion. (no selectively permeable membrane)

9. 9 Water’s journey 3. Up the xylem  Water flows upwards in the xylem both by being pushed and pulled.  Root pressure (minor role) pushes water upwards due to the flow of water by osmosis across the root.  Water is pulled up, as water evaporates from the leaves. (like sucking water up a straw!)- transpiration pull.

10. 10 Water’s journey 3. Up the xylem…. Cont Transpiration pull is due to cohesion and adhesion  Cohesion- the force of attraction between like molecules. i.e. water molecules “stuck together”  Adhesion- the force of attraction between unlike molecules. i.e. water molecules “stuck” to the narrow xylem walls.

11. 11 Water’s journey 4. From the xylem to the leaves  Water diffuses through the permeable cell walls, then along a concentration gradient from cell to cell in the leaf by osmosis.

12. 12 Water’s journey 5. From the leaves to the air  Water evaporates through the moist air spaces within the leaf and finally from the leaf through the stomata.  Insert and complete the “Transpiration” summary diagram.

13. 13 The journey of minerals  Examples include iron and magnesium.  These enter the root from the soil by active transport.  They then move from cell to cell via tiny cytoplasmic connections in plasmodesmata.  Those minerals not required by the root cells are then actively pumped into the xylem.

14. 14 The journey of minerals cont….  Minerals then depend on the transpiration stream for their upward movement in the xylem.  Once at the leaf, the ions are actively transported into the leaf cells.

15. 15 Importance of transpiration Stream  It has 3 benefits: Water is the universal solvent for biochemical reactions Water is required for photosynthesis and maintenance of turgour Evaporation of the water has a cooling effect in hot weather

16. 16 Stomatal mechanism  Stomata are found predominantly on the lower epidermis of leaves.

17. 17 Stomatal mechanism  Stoma are surrounded by guard cells- which control the size of the stoma.

18. 18 Stomatal mechanism  Guard cells differ from normal epidermal cells in 3 ways: Are sausage shaped Have inner cell walls which are thicker and less elastic. Have chloroplasts

19. 19 Stomatal mechanism  During the day: 1. Guard cells take in water and become turgid and swell. 2. This causes the guard cells to buckle- opening the stoma.

20. 20 Stomatal mechanism  During nightime: 1. Guard cells lose water and become plasmolysed/flaccid. 2. This causes the guard cells to reduce in diameter- closing the stoma.  This prevents the plant from losing too much water when it is too dark for photosynthesis.

21. 21 Transpiration animation of stomatal opening

22. 22 Factors affecting transpiration  Anything that increases the rate of evaporation of water will increase the rate of transpiration.  Find out how each of the following effect transpiration: 1. Dark or light 2. Warm or cool 3. Still or moving air 4. Dry or humid air 5. Dry or moist air.

23. 23 Practice Questions  Torrance 1. TYK page 177 Q1-3 2. TYK page 181 Q1&2

24. 24 Adaptation 3 Can you do it?  Understand what is meant by transpiration and transpiration stream.  Describe the movement of water from the soil to the leaves and into the air.  Understand how adhesion and cohesion are involved in transporting water.  Describe the uptake and transport of nutrient ions.  Explain the cooling effect of transpiration.  Explain stomatal mechanism.  Explain how different factors can affect transpiration.