Plants and their structure

1. Plants and their structure

2. General Plant Organization

7. Tissue “Histology is the study of tissues!”

8. Syllabus • An understanding of the relationship between structure and function as exemplified by the following: • parenchyma,collenchyma,sclerenchyma, • xylem & phloem • Epithelium, connective tissues, muscular tissues & nervous tissues.

9. Suggested references • Advanced Biology principles & applications p. 218 – p. 223 • Toole, Glenn., Understanding Biology for Advanced Level (3 ed.). Stanley Thornes (Publishers) Ltd. 1995 • Green, N. P. O., Biological Science. Vol. 1 (2 ed.). Cambridge University Press 1991

10. Definition: tissue • a TISSUE is a group of cells, usually of one kind, & their intercellular substance (e.g. middle lamella in plant & intercellular matrix in animal) which are linked together & perform a particular function

11. Plant tissues

12. Types of plant tissue (1):1. Simple 2. Compund • simple plant tissue (tissue that consists of one type of cell only) • compound plant tissue (tissue that consists of more than one type of cells)

13. Types of plant Tissue (2) 1. Meristematic 2. Permanent • Meristematic tissue • isodiametric • without any intercellular spaces • thin cell wall • dense protoplasm • large nucleus • small or no vacuoles • occurrence : apical and lateral meristem

14. Apical meristem • growing points of stem and root • give rise to primary permanent tissue (primary growth) • Lateral meristem • in cambium • producing secondary permanent tissues (secondary growth)

15. Permanent tissue! • 1. simple 2. compound • types of simple permanent tissue • ~parenchyma • ~collenchyma • ~sclerenchyma

16. A. Parenchyma • Distribution • ~in cortex, pith & packing tissue of vascular tissues ( xylem and phloem) • Shape • ~usually spherical • ~unspecialised cells • ~thin cell wall

17. Parenchyma

18. A. Parenchma (continu.) • Metabolism • ~metabolic active • ~potentially meristematic • Function • ~store food ( starch ) • ~provide support for herbaceous plants • ~intercellular space around parenchyma cells allow exchange of gases

19. Modified parenchyma • Green, N.P.O., Biological Science. Vol.1 (2 ed.). Cambridge University Press 1991: p.219 fig.8.3

20. Epidermis Structure: One cell thick covers the whole of the primary plant body Secrete a waxy substance to form a layer of cuticle Function: Reduce the water loss by evaporation Guard cells Structure: exist in pairs, kidney shape, contain chloroplast Function: Control the size of the stoma Some parenchyma cells:

21. Epidermal Cells

22. Some parenchyma cells: • Mesophyll cells • Structure: • palisade mesophyll, column-shaped, contains many chloroplasts. • Function: • Carry out photosynthesis efficiently • Structure: • Spongy mesophyll, irregular in shape, contains fewer chloroplast • Function: • provide large space to allow efficient gaseous exchange

23. Some parenchyma cells: • Endodermis • Structure: • layer of cells surrounding the vascular tissue • Pericycle • Structure: • One to several cell thick, lied between the central cell and endodermis • Function: • produce lateral root

24. B. Collencyma • Green, N.P.O., Biological Science. Vol.1(2ed.). Cambridge University Press 1991: p.221 fig.8.a, b

25. Collenchyma

27. B. Collencyma • Distribution • outer region of cortex in young stems • Shape • shape similar to parenchyma but thickened cell wall at he corners of cell • elongated

28. B. Collencyma • Function • Give mechanical strength • especially in young plant & herbaceous plant • it is distributed towards the periphery of the region

29. C. Sclerenchyma (fibre) • Green, N.P.O., Biological Science. Vol. 1 (2ed.). Cambridge University Press 1991: p. 222fig.8.5a,b

30. Sclerenchyma

31. C. Sclerenchyma (fibre) • Distribution • found in pericycle of dicotyledonous stems & vascular bundle!

32. C. Sclerenchyma (fibre) • Structure • heavily thickened with deposits of lignin (a complex substances with great strength in the cell wall), even thickening of cell wall. • (stained red under microscope)

33. C. Sclerenchyma • Metabolism • ~mature sclerenchyma cells are dead • Function • ~provide main mechanical support

34. C. Sclerenchyma (fibre) • Shape • Fibres • Elongated sclerenchyma cells • Roughly spherical • Compound plant tissues

35. Compound plant tissue • Plant tissues consists of more than one types of cell • e.g. Xylem • consist of • parenchyma cells • fibres(elongated sclerenchyma cells) • vessels • tracheids

36. xylem: Tracheids • Structure • single cell • elongated & lignified • with tapering end • empty lumen with no cell content

37. Tracheids • Metabolism • ~they are dead with empty lumens when mature • Function • ~provide mechanical strength • ~give support to plant • ~conduct water and mineral salts

38. Xylem: Vessels • Structure • tubular cells • perforated at both ends • formed by joining end to end • shorter & wider than tracheids • thick lignified cell wall

42. Vessels • Metabolism • they are dead when mature • Function • Conduct water & minerals • because they are long & empty • xylem is distributed in centre of the root --> to withstand uprooting force • xylem is distributed in the peripheral region of dicotyledonous stem--> to withstand bending force • Support

43. Xylem: parenchyma • Structure • thin cellulose cell walls & living contents

44. Xylem: fibres • Structure • ~similar to sclerenchyma fibres

45. Compound plant tissue: phloem • Consist of: • ~parenchyma • ~fibres • ~sieve tube element • ~companion cells

46. Phloem • Function • ~translocation of food • ~no mechanical function

49. Phloem • a. Sieve tube cells • Structure • no nucleus(degenerated when mature) • cytoplasm are restricted to edges of the cell • long sieve tube are formed by fusion of sieve tube element & partial break down of the cross walls between them to form sieve plate

50. Phloem • b. Companion cells • Structure • closely associated with the sieve element • Functions • to give energy to sieve tube cells