1. NOTES: CH 35 - Plant Structure & Growth

2. In their evolutionary journey, plants adapted to the problems of a terrestrial existence as they moved from water to land

3. ANGIOSPERMS (flowering plants) -most diverse and widespread of plants (about 275,000 species!) -characterized by FLOWERS and FRUITS (adaptations for reproduction and seed dispersal)

4. *Angiosperms are divided into two taxonomic classes: 1) MONOCOTS 2) DICOTS

6. Terrestrial plants faced a divided habitat:  air is the source of CO 2 for photosynthesis (not dissolved in water)  sunlight cannot penetrate soil  soil provides water and dissolved minerals to plant

7. To accommodate this divided habitat, plants have two basic systems: 1) ROOT SYSTEM (subterranean) 2) SHOOT SYSTEM (aerial)

8. Roots and Shoots are interdependent!!! *Roots depend on shoots for sugar and other organic nutrients *Shoots depend on roots for minerals, water and support

10. THE ROOT SYSTEM: Root structure is well adapted to: > Anchor plants > Absorb and conduct water and nutrients > Store food

11. Two major types of root systems: 1) TAPROOT SYSTEM: -one large, vertical root -provides firm anchorage in soil -modified taproots: carrots, turnips, sweet potatoes

12. 2) FIBROUS ROOT SYSTEM: -mat of threadlike roots spread out below soil -provides exposure to soil water and minerals -roots concentrated in upper few cm of soil -helps to prevent soil erosion

13. *Absorption of water is greatly enhanced by ROOT HAIRS

14. THE SHOOT SYSTEM: Stem morphology includes: -axillary buds = embryonic side shoots in angle of leaf and stem; usually dormant -terminal bud = bud on a shoot tip

16. Growth of a shoot is concentrated at the apex of the shoot (TERMINAL BUD) **the terminal bud inhibits development of axillary buds – this is called APICAL DOMINANCE

17. LEAVES *the main photosynthetic organs of a plant *leaves of monocots and dicots differ: -monocot leaves have parallel veins -dicot leaves have a branched network of veins

18. PLANT CELL OVERVIEW: *Recall: in addition to the structures in other eukaryotic animal cells, PLANT CELLS have unique organelles: -CELL WALL -CHLOROPLASTS -LARGE, CENTRAL VACUOLE -TONOPLAST (membrane around vacuole)

19. Typical Plant Cell

20. Specialized Plant Cells: 1) Parenchyma cells: -least specialized of plant cells -function in synthesizing and storing organic products

22. Specialized Plant Cells: 2) Collenchyma cells: -usually grouped in strands to support young parts of plants -elongate as the stems and leaves grow -e.g.: make up the strings in celery

24. Specialized Plant Cells: 3) Sclerenchyma cells: -function in support -FIBERS: long, slender, tapered cells -SCLERIDS: shorter, irregularly-shaped cells

27. Each organ of a plant (leaf, stem, root) has three tissue systems: 1) DERMAL 2) VASCULAR 3) GROUND

28. DERMAL TISSUE SYSTEM (epidermis) -covers and protects plant -root hairs are extensions of epidermal cells near root tips -waxy CUTICLE secreted by epidermal cells of the leaf and stem

29. VASCULAR TISSUE SYTEM -xylem and phloem -functions in transport and support; continuous throughout plant

30. Specialized Plant Tissues: ● XYLEM: water-conducting vessels ● PHLOEM: sugar / sap-conducting vessels

32. Specialized Plant Tissues (continued): Food-conducting cells of PHLOEM include: ● at least one COMPANION CELL is connected to each phloem segment by openings called PLASMODESMATA

37. GROUND TISSUE SYSTEM -predominantly parenchyma -occupies space between dermal and vascular tissues -functions in: photosynthesis, storage, support

39. PLANT GROWTH!

40. *Plant growth begins with germination of the seed and continues for the lifespan of the plants

41. MERISTEMS: -perpetually embryonic tissues -unspecialized and constantly dividing

42. Two types of plant growth: 1) PRIMARY GROWTH: elongation 2) SECONDARY GROWTH: thickening of roots and shoots

43. -APICAL MERISTEMS: located in root tips and shoot buds; involved in primary growth -LATERAL MERISTEMS: cylinders of dividing cells extending along the lengths of roots and shoots; involved in secondary growth

44. Primary Growth of Roots: root growth is concentrated near its tip and results in roots extending through the soil the root is covered by a ROOT CAP which protects the meristem and secretes a polysaccharide coating that lubricates the soil ahead of the growing root

45. the root tip contains 3 zones of cells: *ZONE OF CELL DIVISION: near tip of root; -includes apical meristem

46. *ZONE OF CELL ELONGATION: above the zone of cell division -cells elongate to at least 10x their original length -elongation of cells here pushes the root tip through the soil

47. *ZONE OF MATURATION: located farthest from the root tip -where new cells become specialized

49. Primary Tissues of Roots: 1) PROTODERM: gives rise to epidermis

50. Primary Tissues of Roots: 2) PROCAMBIUM: forms a STELE (central cylinder) where xylem and phloem develop *difference between monocots and dicots

51. Primary Tissues of Roots: 3) GROUND MERISTEM: -gives rise to ground tissue system; -fills the CORTEX (root area between stele and epidermis); -stores food; -has ENDODERMIS (innermost layer of cortex; forms boundary between cortex and stele)

56. *LATERAL ROOTS may sprout from the outermost layer of the stele (the PERICYCLE)  as a result, the lateral root maintains its vascular connection to the stele of the main root

57. TISSUE ORGANIZATION OF STEMS: vascular tissue is organized into strands of VASCULAR BUNDLES that run the length of the stem; these converge at the shoot  root transition to join the root stele each vascular bundle is surrounded by ground tissue

58. DICOTS: -ground tissue includes PITH (inside) and CORTEX (outside) -bundles arranged in a RING with: XYLEM facing PITH PHLOEM facing CORTEX

62. MONOCOTS: -vascular bundles scattered throughout the ground tissue of stem

64. TISSUE ORGANIZATION OF LEAVES: EPIDERMIS: protects against water loss and pathogens STOMATA: pores flanked by GUARD CELLS which regulate gas exchange and allow for TRANSPIRATION (water loss)  stomata are more numerous on the bottom surface of the leaf…WHY?

65. MONOCOT = parallel veins DICOT = network veins

69. TISSUE ORGANIZATION OF LEAVES: the ground tissue inside the leaf is called: MESOPHYLL -consists mainly of parenchyma cells equipped to perform photosynthesis Mesophyll

70. TISSUE ORGANIZATION OF LEAVES: *Dicots have two mesophyll regions: 1) Palisade parenchyma: upper half of leaf; cells are column- shaped 2) Spongy parenchyma: lower half of leaf; irregularly shaped cells surrounded by air spaces

72. TISSUE ORGANIZATION OF LEAVES: **Vascular bundles from stem branch repeatedly throughout leaf blade forming VEINS  this brings the photosynthetic tissue of the leaf in close contact with the xylem and phloem  also forms a skeleton to support the shape of the leaf

75. SECONDARY GROWTH: results in thickening of stems / roots (seen in gymnosperms & some dicots) results from two lateral meristems: 1) VASCULAR CAMBIUM: produces secondary xylem and phloem 2) CORK CAMBIUM: produces a tough, thick covering for roots and stems that replaces the epidermis

77. VASCULAR CAMBIUM: forms between the 1º xylem and phloem of each vascular bundle a continuous cylinder of dividing cells: -2º xylem cells form towards the inside -2º phloem cells form towards the outside

79. *accumulated layers of 2º xylem produces WOOD

80. VASCULAR CAMBIUM: **forms annual growth rings due to yearly activity: 1) cambium dormancy (winter) 2) spring wood production 3) summer wood production

81. *2º phloem does not accumulate extensively; it becomes part of bark and eventually sloughs off the tree trunk

82. CORK CAMBIUM: cylinder of meristematic tissue that forms in the outer cortex of the stem cork cells form to the outside; as these cells mature, they deposit a waxy material (SUBERIN) in their walls and die these dead cork tissues protect the stem from damage and pathogens and reduce water loss

83. BARK = all tissues external to the vascular cambium  phloem, cork cambium and cork

86. Secondary Growth in Roots: -similar to stems -in roots, the outer layer is impermeable to water…consequently, the roots with 2º growth function to anchor the plant and to transport water and nutrients between the younger roots and the shoot system