1. Plant Structure & Growth
Plant Biology
Chapter 35
Kingdom Plantae
Plant Structure & Growth

2. Plants have evolved two systems: subterranean root system
aerial shoot system of stems and leaves.
shoots
roots

3. Primary Function of Organs
Three organs in plants:
Stem
Leaves
Root
Shoot system

4. Roots Roots anchor the plant in the soil Store food
Absorb minerals and water
Most absorption of water and minerals in occurs near the root tips.

5. Proproots

6. Black Mangrove with Pneumatophore
                                                                                                                                                                                                                             
TPneumatophores allow water-logged roots to obtain Oxygen which is essential for respiration.
Pneumatophores contain lots of Aerenchyma which is abundant in submerged and emergent plant organs.
They may also contain Lenticels which are areas in the dermis which permit the entry of air into structures that are covered by Periderm
his Pneumatophore has a Periderm (Outer Bark) which protects it from the environment but is impervious to air.  However it produces Lenticels which allow for gas exchange with the environment.
Black Mangrove with Pneumatophore

7. Shoots consist of stems and leaves.
Stem: Raises leaves and flowers above ground (safer from herbivores and allow leaves to better photosynthesize). Path by which water, minerals, and food are transported.
Leaves: Site of photosynthesis, i.e. food production

8. Shoots System: stems and leaves Stems
May be vegetative (leaf bearing) or reproductive (flower bearing).
Node- area of stem where leaf is born
Internodes- stem area between nodes
Buds: Stem elongation. Embryonic tissue of leaves and stem (not flower bud)
Terminal bud-Located at tip of stems or branches.
Axillary bud- Gives rise to branches
Apical Dominance: Prevention of branch formation by terminal bud

9. Leaves:Photosynthesis
Shoots System:
Leaves:Photosynthesis
Petiole: Stalk of leaf, joins leaf to node of stem
Blade: Flattened, expanded portion of leaf. Site of photosynthesis

10. Shoot System

11. Modified shoots:
Include stolons, rhizomes, tubers, and bulbs, are often mistaken for roots.
Stolons: allow plants to colonize large area and to reproduce asexually
Pohuehue

12. Rhizomes: horizontal stems that grow underground.
Tubers: are the swollen ends of rhizomes specialized for food storage.
Bulbs: vertical, underground shoots consisting mostly of the swollen bases of leaves that store food.
rhizomes
tubers
bulbs

13. Classification of Leaves
Arrangement on the stem
Simple vs. compound
Overall leaf shape
Leaf margin shape
Leaf venation

14. Leaf Taxonomy

15. Leaf Arrangement on the Stem
Opposite: 2 leaves at a node, on opposite sides of the stem
Spiral: 1 leaf per node, with the second leaf being above the first but attached on the opposite side of the stem
Whorled: 3 or more leaves at a node

16. Leaf Modifications Tendrils Spines Storage Petal-like
Insectivorous leaves

17. Leaf Modifications
tendrils
spines
storage
petal-like

18. Plant organs are composed of three tissue systems:
Dermal tissue
Vascular tissue
Ground tissue

19. Dermal Tissue
The dermal tissue, or epidermis, is generally a single layer of tightly packed cells that covers and protects all young parts of the plant.
Other specialized characteristics :
Root hairs: increased absorption
Cuticle: waxy coating, prevents water loss

20. Plant Cell Structure
cell wall
chloroplast
nucleus
central vacuole

21. Cell Wall Structure secondary cell wall primary cell wall
middle lamella

22. Cell Wall Structure
plasmodesmata

23. Plant Cell Types Xylem Phloem Tracheids Vessel elements
Sieve-tube members
Companion cell

24. Vascular Tissue Vascular tissue: runs continuous throughout the plant
transports materials between roots and shoots.
Xylem transports water and dissolved minerals upward from roots into the shoots (water the xylem)
Phloem transports food from the leaves to the roots and to non-photosynthetic parts of the shoot system (feed the phloem)

25. Xylem
The water conducting elements of xylem are the tracheids and vessel elements.

26. Xylem Tracheids Characteristics Functions tapered elongated cells
connect to each other through pits
secondary cell walls strengthened with lignin
dead at functional maturity
Functions
transport of water plus dissolved minerals
support

27. Xylem Vessel Elements Characteristics Functions
shorter and wider than tracheids
possess thinner cell walls than tracheids
Aligned end-to-end to form long micropipes
dead at functional maturity
Functions
transport of water plus dissolved minerals
support

28. Water conducting cells of the xylem

29. Phloem
Food and minerals move through tubes formed by chains of cells, sieve-tube members.
sieve plates
companion cell

30. Phloem Sieve-tube Members Characteristics Functions
living cells arranged end-to-end to form food-conducting cells of the phloem
lack lignin in their cell walls
mature cells lack nuclei and other cellular organelles
alive at functional maturity
Functions
transport products of photosynthesis

31. Phloem Companion Cells Characteristics Functions
living cells adjacent to sieve-tube members
connected to sieve-tube members via plasmodesmata
Functions
support sieve-tube members
may assist in sugar loading into sieve-tube members

32. Food conducting cells of the phloem

33. Ground Tissue
Ground tissue fills the interior of the plant. It contains three basic cell types:
Parenchyma cells
Collenchyma cells
Sclerenchyma cells
Dermal tissue
Ground tissue
Vascular tissue
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34. Parenchyma Characteristics Functions least specialized cell type
only thin primary cell wall is present
possess large central vacuole
generally alive at functional maturity
Functions
make up most of the ground tissues of the plant
storage
photosynthesis
can help repair and replace damaged organs by proliferation and specialization into other cells

35. Parenchyma

36. Collenchyma Characteristics Functions
possess thicker primary cell walls the that of parenchyma
no secondary cell wall present
generally alive at functional maturity
Functions
provide support without restraining growth

37. Collenchyma

38. Sclerenchyma Characteristics Functions
have secondary cell walls strengthened by lignin
often are dead at functional maturity
two forms: fibers and sclereids
Functions
rigid cells providing support and strength to tissues

39. Two other sclerenchyma cells, fibers and sclereids, are specialized entirely in support.
Fibers are long, slender and tapered, and usually occur in groups.
Those from hemp fibers are used for making rope and those from flax for weaving into linen.
Sclereids, shorter than fibers and irregular in shape, impart the hardness to nutshells and seed coats and the gritty texture to pear fruits.

40. Fiber Cells

41. Sclereids

42. Plant Growth & Development
Growth is the irreversible increase in mass that results from cell division and cell expansion.
Development is the sum of all the changes that progressively elaborate an organism’s body.

43. Meristems generate cells for new organs throughout the lifetime of a plant: an overview of plant growth
Most plants demonstrate indeterminate growth, growing as long as the plant lives.
In contrast, most animals and certain plant organs, such as flowers and leaves, undergo determinate growth, ceasing to grow after they reach a certain size.
Indeterminate growth does not mean immortality.

44. Germination  flowering  seed production death
Plant Lifecycle:
Germination  flowering  seed production death
Annual- in a single year or less.
Many wildflowers and important food crops, such as cereals and legumes, are annuals.
Biennial- spans two years.
Often, there is an intervening cold period between the vegetative growth season and the flowering season.
Perennials- Plants that live many years,
Includes trees, shrubs, and some grasses.
These often die not from old age, but from an infection or some environmental trauma.

45. Meristems– embryonic tissue.
These cells divide to generate additional cells.
Initials- generative cells that remain in the meristem.
Derivatives- Those that are displaced from the meristem,and continue to divide for some time until the cells they produce begin to specialize within developing tissues.

46. The pattern of plant growth depends on the location of meristems.
Fig
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47. Locations of Meristematic Tissues
Apical meristems: located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in length.
Primary growth
initial root and shoot growth
produced by apical meristem
elongation occurs
restricted to youngest parts of the plant, i.e, tips of roots & shoots

48. Locations of Meristematic Tissues
Lateral meristems: allow the plant to increase in girth
Secondary growth: thickening of roots and shoots.
Produced by lateral meristems
Develop in slightly older regions of roots and shoots
Examples: vascular and cork cambium.

49. Meristems

50. Types of Primary Meristems
Protoderm: forms dermal tissue system
Procambium: forms vascular tissue system
Ground Meristem: forms ground tissue system

51. Primary Growth in Roots
Root Cap: covers root tip & protects the meristem as the root pushes through the abrasive soil during primary growth.
The cap also secretes a lubricating slime.
Growth in length is concentrated near the root’s tip, where three zones of cells at successive stages of primary growth are located.
zone of cell division
zone of elongation
zone of maturation
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52. Primary Growth of the Root

53. The zone of cell division includes the apical meristem and its derivatives, primary meristems.
Near the middle is the quiescent center, cells that divide more slowly than other meristematic cells.
These cells are relatively resistant to damage from radiation and toxic chemicals.
They may act as a reserve that can restore the meristem if it becomes damaged.

54. Fig
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55. The zone of cell division blends into the zone of elongation where cells elongate, sometimes to more than ten times their original length.
It is this elongation of cells that is mainly responsible for pushing the root tip, including the meristem, ahead.
The meristem sustains growth by continuously adding cells to the youngest end of the zone of elongation.
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56. In the zone of maturation, cells begin to specialize in structure and function.
In this root region, the three tissue systems produced by primary growth complete their differentiation, their cells becoming functionally mature.
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57. Three primary meristems give rise to the three primary tissues of roots.
The epidermis develops from the dermal tissues.
The ground tissue produces the endodermis and cortex.
The vascular tissue produces the stele, the pericycle, pith, xylem, and phloem.
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58. The protoderm, the outermost primary meristem, produces the single cell layer of the epidermis.
Water and minerals absorbed by the plant must enter through the epidermis.
Root hairs enhance absorption by greatly increasing the surface area.
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59. The procambium gives rise to the stele, which in roots is a central cylinder of vascular tissue where both xylem and phloem develop.
Stele
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60. The ground tissue between the protoderm and procambium gives rise to the ground tissue system.
These are mostly parenchyma cells between the stele and epidermis.
They store food and are active in the uptake of minerals that enter the root with the soil solution.
The innermost layer of the cortex, the endodermis, is a cylinder one cell thick that forms a boundary between the cortex and stele.
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61. Dicot
Monocot
Fig

62. Monocot Root Anatomy epidermis cortex endodermis cortex pericycle
stele
pith
phloem
xylem
pith

63. Dicot Root Anatomy cortex endodermis pericycle epidermis cortex stele
xylem
phloem

64. Each growing season, primary growth produces young extensions of roots and shoots, while secondary growth thickens and strengthens the older part of the plant.

65. Organization of Primary Tissues in Young Stems
Fig

66. Primary Growth of the Shoot

67. Monocot Stem Anatomy phloem epidermis vascular bundles ground tissue
xylem

68. Dicot Stem Anatomy epidermis phloem cortex vascular bundle pith
cambium
xylem

69. The meristematic bands make a continuous cylinder of dividing cells surrounding the primary xylem and pith of the stem.
Fig
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70. This ring of vascular cambium consists of regions of ray initials and fusiform initials.
Ray initials (xylem rays and phloem rays) that transfer water and nutrients laterally
Fusiform initials form 2o xylem to the inside of the vascular cambium and 2o phloem to the outside.
Fig
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71. As secondary growth continues over the years, layer upon layer of secondary xylem accumulates, producing the tissue we call wood.
Wood consists mainly of tracheids, vessel elements (in angiosperms), and fibers.
These cells, dead at functional maturity, have thick, lignified walls that give wood its hardness and strength.

72. Secondary Growth of a Stem

73. Production of Secondary Xylem and Phloem
The accumulation of this tissue over the years accounts for most of the increase in diameter of a woody plant.
Secondary xylem forms to the interior and secondary phloem to the exterior of the vascular cambium.
C=cambium cell
X=2o xylem
P=2o phloem
D=derivative

74. Anatomy of a Tree Trunk
After several years of secondary growth, several zones are visible in a stem.

75. Primary and Secondary Growth in a Woody Stem

76. The Leaf
The leaf epidermis is composed of cells tightly locked together like pieces of a puzzle.
It is the first line of defense against physical damage and pathogenic organisms
The waxy cuticle prevents desiccation.

77. Leaf Anatomy

78. Typical Dicot Leaf X-Section
Cuticle
Epidermis
Palisade Parenchyma
Vascular bundles
Guard Cells
Spongy Parenchyma
Stoma

79. Typical Monocot Leaf X-Section
Bundle sheath cell
Midvein
Vein
Epidermis
Phloem
Xylem
Bulliform Cells
Stoma

80. Guard cells with chloroplasts
Leaf Stomata: Allow Gas Exchange
Guard cells with chloroplasts
Stomata in Zebrina leaf epidermis
Stoma
Subsidiary cells

81. Mesophyll- the ground tissue of the leaf, located between the upper and lower epidermis.
mainly of parenchyma cells equipped with chloroplasts and specialized for photosynthesis.
CO2 and O2 circulate through the air spaces
The air spaces are particularly large near stomata, where gas exchange with the outside air occurs.

82. The vascular tissue of a leaf is continuous with the xylem and phloem of the stem.
Leaf traces, branches of vascular bundles in the stem, pass through petioles and into leaves.
Within a leaf, veins subdivide repeatedly and branch throughout the mesophyll.
xylem brings water and minerals
phloem carries sugars
the vascular infrastructure reinforces the shape of the leaf.

83. Molecular Biology and Plants
Plants have tremendous developmental plasticity.
Environmental factors can influence growth and development, and reproductive output
A broad range of morphologies can result from the same genotype as the plant undergoes three developmental processes: growth, morphogenesis, and differentiation.
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84. Molecular biology is revolutionizing the study of plants
Much plant research has focused on Arabidopsis thaliana, a small weed in the mustard family.
Ideal research subject:
Cultivates quickly
Requires little lab space
Generation time 6 weeks
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85. first plant genome sequenced, taking six years to complete.
Arabidopsis
first plant genome sequenced, taking six years to complete.
Arabidopsis has a total of about 26,000 genes, with fewer than 15,000 different types of genes.
The functions of only about 45% of the Arabidopsis genes are unknown.
Fig
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86. Now plant biologists work to identify the functions of every gene and track every chemical pathway to establish a blueprint for how plants are built.
One key task is to identify which cells are manufacturing which gene products and at what stages in the plant’s life.
Potential to develop a designer plant from a computer model.
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