Leaf anatomy

1. Leaf anatomy

2. Leaf anatomy • Leaves start as outgrowths from apical meristem: leaf primordia.

3. Leaf anatomy • 3 primary meristems • protoderm: becomes __________ • procambium: becomes ___________ • ground meristem: becomes ____________.

4. Leaf anatomy • Epidermis: note cuticle, stomata • Veins with vascular tissues (__________ • __________) • Supply water & nutrients, remove sugars for transport elsewhere.

5. Leaf anatomy • Mesophyll • Parenchyma tissue layers (palisade and spongy: do ____________.

6. Monocot vs dicot anatomy • Stem: Dicot with bundles __________. Pith and cortex present. • Monocot: scattered vascular bundles. No _______________.

7. Monocot vs dicot anatomy • Root: Dicot, < 6 phloem patches, no pith

8. Monocot vs dicot anatomy • Root: Monocot, many _____________, pith present

9. Monocot vs dicot summary • Note root system type: dicot often with single major root axis (taproot system), monocot lacking this (fibrous root system)

10. Plant Growth Phenomena • Hormones: molecules produced in small amounts that change _________________ • _________ • Can inhibit or stimulate processes to occur • 5 major types: • auxins • cytokinins • gibberellins • ethylene • abscisic acid

11. Auxins • Promote stem elongation and growth • Example, ___________. Bending of stem toward light

12. Auxins • Also involved in ______________: suppression of lateral meristems by apical meristem

13. Auxins • Can stimulate production of ______________ roots (roots produced on stem or leaf) • Useful in rooting cuttings (asexual plant reproduction)

14. Cytokinins • Stimulate cell division where auxin is also present • Acts as ____________ hormone (keeps detached leaves green).

15. Gibberellins • Promote stem elongation • Mutant plants with low amounts are _________ (internode lengths short)

16. Ethylene • Promotes fruit ripening • Stimulates ____________ (dropping) of leaves, flowers

17. Abscisic acid • Induces formation of winter buds (bud scales, dormant meristem) • Involved in opening and closing of _____________ • Can cause seed dormancy

18. Other plant growth phenomena • Gravitropism: response of stem/root to gravity • Stems bend away from gravity (___________ gravitropism) • Roots bend toward gravity (_________ gravitropism)

19. Other plant growth phenomena • Mechanism unclear. May involve ________ ________ called statoliths (in root cap of root, in parenchyma cells of stem)

20. Other plant growth phenomena • Thigmotropism: response of plant to __________ • Examples: Many tendrils grow toward stimulus and wrap around object

21. Turgor movement • Not growth: involves loss of water pressure (turgor pressure) in some cells • Can be reversed • May involve rapid movement (electrical signal) • Ex, sensitive plant

22. Flowering • Some plants use daylength as flowering cue • Can measure length of night (photoperiod) by pigment called ______________

23. Flowering • Long day plants: flower when night is ________ than some critical time • Short day plants: flower when night is _______ than some critical time • Day neutral plants: don’t use photoperiod as flowering cue

24. Flowering • Use: Can make some plants bloom when we want them • Ex, poinsettia. A short-day plant that growers make flower for Christmas holidays.

25. Plant transport • Phloem: sugars and water (often from leaf to root) • Xylem: water and minerals from root to shoot • Movement driven by _____________: measure of tendency of water to move from one place to another

26. Plant transport • Water potential is affected by: • solutes (high solutes = ______ tendency to move) • pressure (high pressure = ______ tendency to move) • tension (pull: high tension = ______ tendency to move).

27. Water transport • Xylem: water and minerals from root to shoot • How much of water remains in plant? <____%!

28. Water transport • Transpiration: evaporation of water from leaves • Driven by _______ from leaves. Water under tension. Water potential high in soil and low in air.

29. Water transport • Driven by pull from leaves. Water under tension. Water potential high in soil and low in air.

30. Water transport • Transpiration greatly controlled by stomata • Stomata open in ________ but can close if plant lacks sufficient water. Stomata!

31. Sugar transport • Phloem: sugars and water • Flow from ______ to _____ • Pressure flow mechanism

32. Sugar transport • Source: lots of sugar dissolved in water. Generates pressure as water flows in to _______ sugar • Sink: little sugar dissolved in water. Low pressure as water flows out • Creates ___________ gradient that moves fluid thru sieve tubes.

33. Sugar transport • Result: sugar flows to wherever demand is high

34. Secondary Growth

35. Secondary Growth • Two types of growth • Primary growth: up and down. Generated by apical meristems. Form _________ tissues • Secondary growth: growth in girth. Generated by lateral (secondary meristems). Form __________ tissues. • All plants do primary growth • Woody plants do __________ growth

36. Secondary Growth • Lateral meristems • 1) ______________: makes new phloem and xylem • Called ________ phloem and xylem tissues (vs. primary phloem and xylem made directly from procambium) • Function: xylem takes water + minerals to leaves, phloem takes sugars to roots

37. Secondary Growth • Lateral meristems • 2) ___________: makes new cell type, cork cell. Cork cells with primary wall impregnated with waxy material (_______). Dead at maturity. Forms waterproof layer on outside of body to replace epidermis. • _________: Tissue composed of cork cells and made by cork cambium. Also is a secondary tissue.

38. Secondary Growth • Stem cross section

39. Secondary Growth • Vascular bundles contain __________________ • Located between primary xylem and phloem • Meristematic: can still do _______________

40. Secondary Growth • Residual procambium cells start to divide • Produce new cells ______________

41. Secondary Growth • Parenchyma cells between bundles also start to divide • Together form solid ring of cells, all dividing laterally • This is __________________

42. Secondary Growth • Vascular cambium makes secondary xylem on __________, secondary phloem on __________ • Note how cambium moves outward over time

43. Secondary Growth • Note arrangement of primary phloem and secondary phloem, primary xylem and secondary xylem

44. Secondary Growth • Secondary xylem may contain: • 1) Vessel elements • 2) Tracheids • 3) ____________ • 4) Fibers • Secondary phloem may contain: • 1) Sieve tube elements • 2) Companion cells • 3) Parenchyma • 4) ___________

45. Secondary Growth • Two

46. Secondary Growth • Later secondary growth

47. Secondary Growth • First cork cambium: Forms under ___________

48. Secondary Growth • Cork cambium: Makes files of cork cells to outside. Forms first __________. Epidermis cut off from rest of stem and dies.

49. Secondary Growth • Problem: cork cells are dead at maturity. Cork layer cannot _________ as vascular cambium continues to grow. • Solution: form new ______ ______ in cortex under old one • After time, several __________ build up (yellow lines). Newest (inner) one cuts off water to layers beyond it and they _______.

50. Secondary Growth • Periderm replaces epidermis. How get _______ into stem?