1. Chapter 35: Plants, Plants and more…Wait for it…. Plants
Lecture by: Professor Rodriguez
Modified from Campbell's slides
Chapter 35: Plants, Plants and more…Wait for it…. Plants

2. The Three Basic Plant Organs
Roots, Stems, and Leaves
Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below ground and above ground
Plants take up water and minerals from below ground
Plants take up CO2 and light from above ground
Organized into a root system and a shoot system

4. Roots A root is an organ with important functions:
Anchoring the plant
Absorbing minerals and water
Storing carbohydrates
Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system
Monocots and eudicots are the two major groups of angiosperms

5. Eudicots vs Monocots
Most eudicots and gymnosperms have a taproot system, which consists of:
A taproot, the main vertical root
Lateral roots, or branch roots, that arise from the taproot
Most monocots have a fibrous root system, which consists of:
Adventitious roots that arise from stems or leaves
Lateral roots that arise from the adventitious roots

6. Root Hairs
In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area
Many plants have root adaptations with specialized functions
Figure 35.3

7. Stems A stem is an organ consisting of
An alternating system of nodes, the points at which leaves are attached
Internodes, the stem segments between nodes
An axillary bud is a structure that has the potential to form a lateral shoot, or branch
An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot

8. Leaves
The leaf is the main photosynthetic organ of most vascular plants
Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem
Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves
Most monocots have parallel veins
Most eudicots have branching veins
In classifying angiosperms, taxonomists may use leaf morphology as a criterion

9. Check this out
Figure 35.6 Simple versus compound leaves.

10. Some plant species have evolved modified leaves that serve various functions
Figure 35.7 Evolutionary adaptations of leaves.

11. Dermal, Vascular, and Ground Tissues
Each plant organ has dermal, vascular, and ground tissues
Each of these three categories forms a tissue system
Each tissue system is continuous throughout the plant

12. Dermal tissue Ground tissue Vascular tissue Figure 35.8
Figure 35.8 The three tissue systems.
Dermal tissue
Ground tissue
Vascular tissue

13. Tissues
In nonwoody plants, the dermal tissue system consists of the epidermis
A waxy coating called the cuticle helps prevent water loss from the epidermis
In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots
Trichomes are outgrowths of the shoot epidermis and can help with insect defense

14. Vascular tissues
The vascular tissue system carries out long-distance transport of materials between roots and shoots
The two vascular tissues are xylem and phloem
Xylem conveys water and dissolved minerals upward from roots into the shoots
Phloem transports organic nutrients from where they are made to where they are needed

15. Vascular tissues
The vascular tissue of a stem or root is collectively called the stele
In angiosperms the stele of the root is a solid central vascular cylinder
The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem

16. Ground Tissues
Tissues that are neither dermal nor vascular are the ground tissue system
Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex
Ground tissue includes cells specialized for storage, photosynthesis, and support

17. Common Types of Plant Cells
Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function
The major types of plant cells are:
Parenchyma
Collenchyma
Sclerenchyma
Water-conducting cells of the xylem
Sugar-conducting cells of the phloem

18. Parenchyma Cells Mature parenchyma cells
Have thin and flexible primary walls
Lack secondary walls
Are the least specialized
Perform the most metabolic functions
Retain the ability to divide and differentiate

19. Collenchyma Cells
Collenchyma cells are grouped in strands and help support young parts of the plant shoot
They have thicker and uneven cell walls
They lack secondary walls
These cells provide flexible support without restraining growth

20. Sclerenchyma Cells
Sclerenchyma cells are rigid because of thick secondary walls strengthened with lignin
They are dead at functional maturity
There are two types:
Sclereids are short and irregular in shape and have thick lignified secondary walls
Fibers are long and slender and arranged in threads

21. Tracheids and vessels (colorized SEM) Pits
Figure 35.10d
Vessel
Tracheids
Tracheids and vessels (colorized SEM)
Pits
Figure Exploring: Examples of Differentiated Plant Cells
Perforation plate
Vessel element
Vessel elements, with perforated end walls
Tracheids

22. Sieve-tube elements: longitudinal view (LM) 3 m
Sieve plate
Sieve-tube element (left) and companion cell: cross section (TEM)
Companion cells
Sieve-tube elements
Figure 35.10e
Plasmodesma
Sieve plate
Figure Exploring: Examples of Differentiated Plant Cells
30 m
Nucleus of companion cell
15 m
Sieve-tube elements: longitudinal view
Sieve plate with pores (LM)

23. Concept 35.2 Meristems generate cells for primary and secondary growth
A plant can grow throughout its life; this is called indeterminate growth
Some plant organs cease to grow at a certain size; this is called determinate growth

24. Apical Meristems
Meristems are perpetually embryonic tissue and allow for indeterminate growth
Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots
Apical meristems elongate shoots and roots, a process called primary growth

25. Lateral meristems
Lateral meristems add thickness to woody plants, a process called secondary growth
There are two lateral meristems: the vascular cambium and the cork cambium
The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem
The cork cambium replaces the epidermis with periderm, which is thicker and tougher

26. Figure 35.11 Primary growth in stems Epidermis Cortex Primary phloem
Shoot tip (shoot apical meristem and young leaves)
Axillary bud meristem
Root apical meristems
Vascular cambium
Cork cambium
Lateral meristems
Primary growth in stems
Epidermis
Cortex
Primary phloem
Primary xylem
Pith
Secondary growth in stems
Primary phloem
Secondary phloem
Vascular cambium
Secondary xylem
Periderm
Figure An overview of primary and secondary growth.

27. Meristems and Growth Meristems give rise to:
Initials, also called stem cells, which remain in the meristem
Derivatives, which become specialized in mature tissues
In woody plants, primary growth and secondary growth occur simultaneously but in different locations

28. This year’s growth (one year old) Leaf scar
Apical bud
Bud scale
Axillary buds
This year’s growth (one year old)
Leaf scar
Node
Bud scar
One-year-old side branch formed from axillary bud near shoot tip
Internode
Figure 35.12
Last year’s growth (two year old)
Leaf scar
Stem
Figure Three years’ growth in a winter twig.
Bud scar
Growth of two years ago (three years old)
Leaf scar

29. Life cycles
Flowering plants can be categorized based on the length of their life cycle
Annuals complete their life cycle in a year or less
Biennials require two growing seasons
Perennials live for many years

30. Concept 35.3: Primary growth lengthens roots and shoots
Primary growth produces the parts of the root and shoot systems produced by apical meristems

31. Primary Growth of Roots
The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil
Growth occurs just behind the root tip, in three zones of cells:
Zone of cell division
Zone of elongation
Zone of differentiation, or maturation

32. Zone of differentiation Ground Root hair Vascular
Cortex
Vascular cylinder
Key to labels
Epidermis
Dermal
Zone of differentiation
Ground
Root hair
Vascular
Zone of elongation
Figure 35.13
Figure Primary growth of a root.
Zone of cell division (including apical meristem)
Mitotic cells
100 m
Root cap

33. Primary Growth
The primary growth of roots produces the epidermis, ground tissue, and vascular tissue
In angiosperm roots, the stele is a vascular cylinder
In most eudicots, the xylem is starlike in appearance with phloem between the “arms”
In many monocots, a core of parenchyma cells is surrounded by rings of xylem then phloem

34. Core of parenchyma cells
Figure 35.14
Epidermis
Cortex
Endodermis
Vascular cylinder
Pericycle
Core of parenchyma cells
Xylem
100 m
Phloem
100 m
(a)
Root with xylem and phloem in the center (typical of eudicots)
(b)
Root with parenchyma in the center (typical of monocots)
50 m
Key to labels
Figure Organization of primary tissues in young roots.
Endodermis
Pericycle
Dermal
Xylem
Ground
Phloem
Vascular

35. Root with xylem and phloem in the center (typical of eudicots)
Figure 35.14aa
Epidermis
Key to labels
Cortex
Endodermis
Dermal
Vascular cylinder
Ground
Vascular
Pericycle
Xylem
Phloem
Figure Organization of primary tissues in young roots.
100 m
(a)
Root with xylem and phloem in the center (typical of eudicots)

36. 50 m Endodermis Pericycle Xylem Phloem Key to labels Dermal Ground
Figure 35.14ab
50 m
Endodermis
Pericycle
Xylem
Phloem
Key to labels
Figure Organization of primary tissues in young roots.
Dermal
Ground
Vascular

37. Core of parenchyma cells
Epidermis
Key to labels
Cortex
Dermal
Endodermis
Ground
Vascular
Vascular cylinder
Pericycle
Core of parenchyma cells
Figure Organization of primary tissues in young roots.
Figure 35.14b
Xylem
Phloem
100 m
(b)
Root with parenchyma in the center (typical of monocots)

38. Ground Tissue
The ground tissue, mostly parenchyma cells, fills the cortex, the region between the vascular cylinder and epidermis
The innermost layer of the cortex is called the endodermis
The endodermis regulates passage of substances from the soil into the vascular cylinder

39. Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder
Emerging lateral root
Cortex
Vascular cylinder
Pericycle
Figure The formation of a lateral root. 1
Figure

40. Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder
Epidermis
Emerging lateral root
Lateral root
Cortex
Vascular cylinder
Pericycle
Figure The formation of a lateral root. 1 2
Figure

41. Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder
Epidermis
Emerging lateral root
Lateral root
Cortex
Vascular cylinder
Pericycle
Figure The formation of a lateral root. 1 2 3
Figure

42. Primary Growth of Shoots
A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip
Leaves develop from leaf primordia along the sides of the apical meristem
Axillary buds develop from meristematic cells left at the bases of leaf primordia

43. Developing vascular strand
Shoot apical meristem
Leaf primordia
Young leaf
Developing vascular strand
Figure 35.16
Figure The shoot tip.
Axillary bud meristems
0.25 mm

44. Tissue Organization of Stems
Lateral shoots develop from axillary buds on the stem’s surface
In most eudicots, the vascular tissue consists of vascular bundles arranged in a ring
In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring

45. Figure 35.17 Phloem Xylem Sclerenchyma (fiber cells) Ground tissue
Ground tissue connecting pith to cortex
Pith
Epidermis
Figure Organization of primary tissues in young stems.
Key to labels
Epidermis
Cortex
Vascular bundles
Vascular bundle
Dermal
1 mm
1 mm
Ground
(a)
Cross section of stem with vascular bundles forming a ring (typical of eudicots)
(b)
Vascular
Cross section of stem with scattered vascular bundles (typical of monocots)

46. Tissue Organization of Leaves
The epidermis in leaves is interrupted by stomata, which allow CO2 and O2 exchange between the air and the photosynthetic cells in a leaf
Each stomatal pore is flanked by two guard cells, which regulate its opening and closing
The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis

47. The mesophyll of eudicots has two layers:
The palisade mesophyll in the upper part of the leaf
The spongy mesophyll in the lower part of the leaf; the loose arrangement allows for gas exchange
The vascular tissue of each leaf is continuous with the vascular tissue of the stem
Veins are the leaf’s vascular bundles and function as the leaf’s skeleton
Each vein in a leaf is enclosed by a protective bundle sheath

48. Surface view of a spiderwort (Tradescantia) leaf (LM) Cuticle Stoma
Guard cells
Key to labels
Figure 35.18
Stomatal pore
Dermal
Ground
Epidermal cell
50 m
Vascular
Sclerenchyma fibers
(b)
Surface view of a spiderwort (Tradescantia) leaf (LM)
Cuticle
Stoma
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Bundle- sheath cell
Figure Leaf anatomy.
Lower epidermis
100 m
Xylem
Vein
Cuticle
Phloem
Guard cells
Guard cells
Vein
Air spaces
(a) Cutaway drawing of leaf tissues
(c)
Cross section of a lilac (Syringa) leaf (LM)

49. (a) Cutaway drawing of leaf tissues
Figure 35.18a
Key to labels
Sclerenchyma fibers
Dermal
Cuticle
Stoma
Ground
Vascular
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Bundle- sheath cell
Figure Leaf anatomy.
Lower epidermis
Xylem
Vein
Cuticle
Phloem
Guard cells
(a) Cutaway drawing of leaf tissues

50. Concept 35.4
Secondary growth increases the diameter of stems and roots in woody plants
Secondary growth occurs in stems and roots of woody plants but rarely in leaves
The secondary plant body consists of the tissues produced by the vascular cambium and cork cambium
Secondary growth is characteristic of gymnosperms and many eudicots, but not monocots

51. Primary and secondary growth in a two-year-old woody stem
Pith
(a)
Primary and secondary growth in a two-year-old woody stem
Primary xylem
Vascular cambium
Epidermis
Primary phloem
Cortex
Cortex
Primary phloem
Epidermis
Vascular cambium
Primary xylem
Pith
Periderm (mainly cork cambia and cork)
Figure Primary and secondary growth of a woody stem.
Secondary phloem
Secondary xylem
Figure 35.19a-1

52. Primary and secondary growth in a two-year-old woody stem
Pith
(a)
Primary and secondary growth in a two-year-old woody stem
Primary xylem
Vascular cambium
Epidermis
Primary phloem
Cortex
Cortex
Primary phloem
Epidermis
Vascular cambium
Growth
Vascular ray
Primary xylem
Secondary xylem
Pith
Secondary phloem
First cork cambium
Cork
Periderm (mainly cork cambia and cork)
Figure Primary and secondary growth of a woody stem.
Secondary phloem
Secondary xylem
Figure 35.19a-2

53. Primary and secondary growth in a two-year-old woody stem
Pith
(a)
Primary and secondary growth in a two-year-old woody stem
Primary xylem
Vascular cambium
Epidermis
Primary phloem
Cortex
Cortex
Primary phloem
Epidermis
Vascular cambium
Growth
Vascular ray
Primary xylem
Secondary xylem
Pith
Secondary phloem
First cork cambium
Cork
Periderm (mainly cork cambia and cork)
Growth
Figure Primary and secondary growth of a woody stem.
Most recent cork cambium
Cork
Secondary phloem
Bark
Layers of periderm
Secondary xylem
Figure 35.19a-3

54. Figure 35.19b Secondary phloem Bark Vascular cambium Cork cambium
Late wood
Secondary xylem
Periderm
Early wood
Cork
0.5 mm
Figure Primary and secondary growth of a woody stem.
Vascular ray
Growth ring
(b)
Cross section of a three-year- old Tilia (linden) stem (LM)
0.5 mm

55. The Vascular Cambium and Secondary Vascular Tissue
The vascular cambium is a cylinder of meristematic cells one cell layer thick
It develops from undifferentiated parenchyma cells
In cross section, the vascular cambium appears as a ring of initials (stem cells)
The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside

56. Counting the rings
Dendrochronology is the analysis of tree ring growth patterns and can be used to study past climate change
As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals
The outer layers, known as sapwood, still transport materials through the xylem
Older secondary phloem sloughs off and does not accumulate

57. Growth ring Vascular ray Heartwood Secondary xylem Sapwood
Figure 35.22
Growth ring
Vascular ray
Heartwood
Secondary xylem
Sapwood
Figure Anatomy of a tree trunk.
Vascular cambium
Secondary phloem
Bark
Layers of periderm

58. Development
Development consists of growth, morphogenesis, and cell differentiation
Growth is an irreversible increase in size
Morphogenesis is the development of body form and organization
Cell differentiation is the process by which cells with the same genes become different from each other

59. Growth: Cell Division and Cell Expansion
By increasing cell number, cell division in meristems increases the potential for growth
Cell expansion accounts for the actual increase in plant size

60. The Plane and Symmetry of Cell Division
New cell walls form in a plane (direction) perpendicular to the main axis of cell expansion
The plane in which a cell divides is determined during late interphase
Microtubules become concentrated into a ring called the preprophase band that predicts the future plane of cell division

61. Leaf Morphology: Overexpression
Figure Overexpression of a Hox-like gene in leaf formation.

62. Leaves produced by adult phase of apical meristem
Figure 35.32
Figure Phase change in the shoot system of Acacia koa.
Leaves produced by juvenile phase of apical meristem