Transport in Plants (part 2): Xylem, phloem and absorption of water & mineral salts

1. Vascular tissues 1. Xylem 2. Phloem Copyright © 2010 All Rights Reserved

2. Copyright © 2010 All Rights Reserved

3. Xylem tissue Function transports water and mineral salts from ⚫ roots → stem → leaves Unidirectional composed of hollow, nonliving cells (continuous lumen) provides mechanical support to plant because of lignified walls ⚫ ⚫ ⚫ Copyright © 2010 All Rights Reserved

4. Xylem Copyright © 2010 All Rights Reserved

5. Different types of lignin deposits pitted annular rings spiral/helical bands Copyright © 2010 All Rights Reserved

6. Phloem tissue Transports manufactured food (sucrose and amino acids), usually from leaves → other parts of the plant ⚫ Bi-directional ⚫ Consists mainly of 1. sieve tubes 2. companion cells Copyright © 2010 All Rights Reserved

7. Sieve tube ⚫ Consists of sieve tube cells ⚫ Cross walls separating the cells are perforated by minute pores (sieve plates) ⚫ Transport occurs through cytoplasm by diffusion and active transport Transverse Longitudinal Copyright © 2010 All Rights Reserved

8. Sieve plates Copyright © 2010 All Rights Reserved

9. Companion cells ⚫ accompanies sieve tube cells ⚫ helps keep it alive (sieve tubes have degenerate protoplasm) ⚫ assist in transport of manufactured food Copyright © 2010 All Rights Reserved

10. Structure of phloem Copyright © 2010 All Rights Reserved

11. Transport of solutes in the phloem ⚫ Sugars are actively loaded into the phloem in the leaves, and actively removed from the phloem in parts of the plant like the roots that need sugar ⚫ Any sugar that leaks out is pumped back in by the companion cells ⚫ Water follows by osmosis, and the difference in water potential between the leaves (high sucrose, low water potential) and the roots (low sucrose, high water potential) drives a bulk flow of the sugar solution Copyright © 2010 All Rights Reserved

12. Pressure flow concept Copyright © 2010 All Rights Reserved

13. Translocation studies Translocation: transport of a substance through a plant from the site of absorption to other parts of the plant Copyright © 2010 All Rights Reserved

14. Lesson Objectives Translocation studies Structure of roots Transport of water and mineral salts into roots 3 mechanisms of xylem transport Root pressure Capillary action Transpiration pull ⚫ ⚫ ⚫ ⚫ 1. 2. 3. Copyright © 2010 All Rights Reserved

15. 1) Use of aphids ⚫ Proboscis penetrate leaf/stem of plant ⚫ Anaesthetize aphid with CO2 ⚫ Body cut off leaving proboscis in plant tissue ⚫ Liquid exude from proboscis cut end ⚫ Analysis shows liquid = sucrose + amino acids Copyright © 2010 All Rights Reserved

16. More on aphids… Copyright © 2010 All Rights Reserved

17. More on aphids… Copyright © 2010 All Rights Reserved

18. 2) Use of isotopes ⚫14C radioactive carbon isotope ⚫ Presence detected by X- ray photographic film Pg. 178 textbook Copyright © 2010 All Rights Reserved

19. Use of isotopes (continued…) sunlight Carbon dioxide + water → glucose + oxygen + water vapour chlorophyll Sunlight CO2+ H2O → C6H12O6+ O2+ H2O chlorophyll Sunlight 14CO2+ H2O → 14C6H12O6+ O2+ H2O chlorophyll Copyright © 2010 All Rights Reserved

20. Use of isotopes (continued…) Copyright © 2010 All Rights Reserved

21. Transport of water Copyright © 2010 All Rights Reserved

22. Copyright © 2010 All Rights Reserved

23. Structure of root Copyright © 2010 All Rights Reserved

24. Structure of root: Zone of cell division (growing zone): actively dividing young cells (mitosis) Zone of elongation: cells elongate → increase root length Root cap: Covers the root tip → protects cells from injury Zone of maturation/root hairs: Region where most water + mineral salts absorbed Copyright © 2010 All Rights Reserved

25. Entry of water into the plant Thin film around particle = dilute solution of mineral salts Copyright © 2010 All Rights Reserved

26. Entry of water from soil Plasma membrane of root hair cell Soil solution Sap in root hair Strong solution of sugars and salts Dilute solution of mineral salts H2O Higher water potential Low water potential Osmosis Copyright © 2010 All Rights Reserved

27. High water potential Low water potential Copyright © 2010 All Rights Reserved

28. Transport of water from root hair → xylem Copyright © 2010 All Rights Reserved

29. Transport of mineral salts Copyright © 2010 All Rights Reserved

30. Transport of mineral salts Plasma membrane of root hair cell Soil solution Sap in root hair Mineral salts Mineral concentration low Mineral concentration high Diffusion Copyright © 2010 All Rights Reserved

31. Why diffusion and not osmosis? Osmosis It involves flow of solvent molecules in one direction Diffusion Flow of either solute or solvent molecules is in both directions It requires partially permeable membrane No such membrane is required It is a slow process It is a fast process Occurs only in liquids Occurs in liquids as well as gases The movement is over a short distance Movements are over large distances Copyright © 2010 All Rights Reserved

32. Transport of mineral salts Qn: Can the root hair absorb ions if the concentration is higher in the root hair sap compared to the soil solution? Yes!!! Plasma membrane of root hair cell Soil solution Sap in root hair Mineral salts? Mineral concentration high Mineral concentration low Active transport Copyright © 2010 All Rights Reserved

33. Low water potential High water potential Copyright © 2010 All Rights Reserved