Entry of water into plants

1. Entry of water into plants

2. Vascular tissues Root Stem Phloem Xylem Xylem and phloem alternate with each other and found at the centre of a root Xylem and phloem in ‘vascular bundle’ , arranged in a ring around the pith.

3. Absorption of water by roots Root hair cell has Large surface area : volume ratio for efficient absorption Root hair Epidermal layer and root hair cell  Piliferous layer

4. Water would enter root hair cell by osmosis. Root hair cell Soil Dilute solution of mineral salt. Higher water potential High conc. of sugar and salts Lower water potential

5. Absorption of water by roots Water would pass from root hair cell to the inner cell by osmosis B A Lower water potential Higher water potential

6. Water would pass from one cell to the next cell in the cortex until the water enters the xylem tube Cortex – cells in between epidermis and xylem

7. http://www.kscience.co.uk/animations/transpiration.swf

9. Absorption of mineral salts by roots • Ions enter mainly by active transport • Energy from cellular respiration Lower conc. of ions (K, Na) Higher conc. of ions

10. Absorption of mineral salts by roots • Ions also by diffusion (not common) Higher conc. of mineral ions Lower conc. of ions

11. Think about it This plant has been given excessive potassium fertilizer. Explain why the plant will die although fertilizer is suppose to support plant growth.

12. Recap • What is the main process by which water moves from cell to cell and finally into the xylem vessel called?

13. Recap ! http://www.kscience.co.uk/animations/anim_1.htm

14. Recap! • Mineral salts enter the root hair cell mainly by ______________.

15. Moving water up the xylem vessels

16. Moving water up the xylem vessels • Via 3 processes: • Root pressure • Capillary action • Transpiration pull  the main process

17. Process 1: Root pressure

18. What will happen to the water level? Water level Pump water in B A

19. Movement of water from the root hair cells to the xylem vessels would create an upward force to push the water up the xylem vessels. This is known as root pressure.

20. How is root pressure generated? 1) Ions pumped from cortex into xylem Angular in shape Cell in coretx xylem 2) Water enters by osmosis

21. Movement of water from the root hair cells to the xylem vessels would create an upward force to push the water up the xylem vessels. This is known as root pressure.

22. A demonstration to show root pressure What would happen to the water level after 5 hrs? Glass tubing Cut stem with roots Connector

23. A experiment to demonstrate capillary action. • What did you observe?

24. Capillary action • Movement of water up a narrow tube The narrower the tube, the higher level the water level

25. Capillary action 1 2 Force of attraction between water molecules and wall of vessel ‘pulls’ water molecules into a vessel. (adhesion force) Force of attraction between water molecules ‘pull’ the next molecule along. (cohesion force)

26.  Transpiration pull is a suction force caused by transpiration, that pulls the water up the xylem tube. • It is the strongest force that moves water up a xylem tube.

27. Do not be confuse between….. • Transpiration  evaporation of water • Transpiration pull  suction force • Transpiration stream the stream of water up the xylem vessels

28. Adhesion and cohesion forces move the stream of water molecules up a xylem vessel. 3

29. 1) Water continuously moves out of mesophyll cells to form a thin layer of moisture. 2)water evaporates from the thin film of moisture and moves into the intercellular air spaces as water vapour.

30. Moving water up the xylem vessels • Via 3 processes: • Root pressure • Capillary action • Transpiration pull  the main process the causes water to move up a xylem tube.

31. Transpiration What is transpiration? • The evaporation loss of water vapour through the stomata of the leaves is known as transpiration.

32. How is the suction force being created at the leaves by transpiration?

33. Transpiration occurs here

34. Water evaporates from the thin film of moisture to give water vapour. Lower conc. of water vapour Water vapour would move down the concentration gradient into the atmosphere.

35. XYLEM B Water moves out of mesophyll cells to replace the thin film of moisture surrounding the mesophyll cell. Mesophyll cell A

36. Transpiration set up an suction force to pull water up the xylem tube

37. True or false • When transpiration stops for a long time, photosynthesis ceases. • The sun provides energy for water to moves through the xylem.

38. Think about it! • Usually, only 99% of the water absorbed is lost through transpiration. • Where is the remaining 1% of water?

39. Importance of transpiration • To pull water and mineral salts from roots to leaves. • Evaporation of water cools the leaves. • Water used for photosynthesis; to keep cell frim and turgid.

40. Factors affecting the rate of transpiration • Humidity • Wind or air movement • Temperature • Light

41. Humidity • What is humidity? - >Refers to the amount of water vapour that the air can hold.

42. Higher conc. of water vapour (100% saturated) Lower conc. of water vapour The drier the air, the steeper the concentration gradient, the faster the rate of transpiration.

43. Wilting Rate of transpiration > rate of absorption of water What happens to the leaves when they wilt? How does wilting benefit the plant?