1. Chapter 35: Plant Structure, Growth, and Development
Mrs. Valdes
AP Biology

2. Developmental Plasticity
DEFINE: ability to alter itself in response to its environment
more marked in plants than animals
environment more greatly affects phenotype than genetic make-up
plant species by natural selection accumulate characteristics of morphology that vary little within the species
TWO types of leaves 

3. Concept 35.1: The plant body has a hierarchy of organs, tissues, and cells
Plants have organs composed of different tissues, composed of cells
Three basic organs:
Roots
Stems
Leaves
Basic morphology of vascular plants reflect evolution as organisms that draw nutrients from below ground and to be used above ground
Organs organized into root system and shoot system
Roots rely on sugar produced by photosynthesis in shoot system
Shoots rely on water and minerals absorbed by root system

4. Roots Roots: multicellular organs with important functions:
Anchor plant
Absorb minerals and water
Store organic nutrients
Taproot system: consists of one main vertical root that gives rise to lateral roots, or branch roots
Adventitious roots: arise from stems or leaves
Seedless vascular plants and monocots:
have fibrous root system characterized by thin lateral roots with no main root
Most plants absorption of water and minerals occurs near root hairs, where vast numbers of tiny root hairs increase the surface area
Prop Roots: Aid in support of tall, top-heavy plants; Storage Roots: store food & water in roots; “Strangling” aerial roots: seeds of strangler fig tree germinate in branches of other trees, then send lots of aerial roots around host tree until it is totally shaded out and dies; Buttress roots: Look like buttress and support large trunk; Pneumatophores: “air roots”; roots go above water to get oxygen since oxygen is poor in muddy mangrove waters

5. Prop Roots: Aid in support of tall, top-heavy plants
Storage Roots: store food & water in roots;
“Strangling” aerial roots: seeds of strangler fig tree germinate in branches of other trees, then send lots of aerial roots around host tree until it is totally shaded out and dies
Buttress roots: Look like buttress and support large trunk
Pneumatophores: “air roots”; roots go above water to get oxygen since oxygen is poor in muddy mangrove waters

6. Stems Stem: organ consisting of :
alternating system of nodes, points at which leaves are attached
Internodes: stem segments between nodes
Axillary bud: structure that has potential to form a lateral shoot, or branch
Apical bud: AKA terminal bud; located near shoot tip and causes elongation of young shoot
Apical dominance: helps to maintain dormancy in most nonapical buds
Rhizomes: horizontal shoot that grows just below surface

7. Rhizomes: horizontal shoot that grows just below surface; vertical shoots arise from axillary buds on rhizome
Bulbs: vertical underground shoots consisting of mostly enlarged bases of leaves that store food
Stolons: horizontal shoots that grow along surface; “runners” enable plant to reproduce asexually
Tubers: enlarged ends of rhizomes or stolons that specialize in storing food

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

9. Tendrils: usually modified leaves but can be modified stems; “lassoed” support anchors plant and brings it closer to support
Spines: modified leaves; photosynthesis carried out by fleshy green part of cacti
Storage leaves: most succulents modified to store water
Reproductive leaves: adventitious plantlets can fall off and take root in soil
Bracts: NOT petals but modified leaves that surround a group of flowers

10. Dermal, Vascular, and Ground Tissues
Each plant organ has dermal, vascular, and ground tissues
Tissue system: functional unit connecting all plant’s organs
Dermal tissue system: plants outer protective covering
Cuticle: waxy coating helps prevent water loss from epidermis
Periderm: in woody plants, protective tissues that replace epidermis in older regions of stems and roots
Trichomes: outgrowths of shoot epidermis; can help with insect defense

11. Stele: vascular tissue of stem or root
Vascular tissue system: carries out long-distance transport of materials between roots and shoots
two vascular tissues :
Xylem: conveys water and dissolved minerals upward from roots into the shoots
Phloem: transports organic nutrients (FOOD) from where they are made to where they are needed
Stele: vascular tissue of stem or root
In angiosperms stele of root is a solid central vascular cylinder
stele of stems and leaves divided into vascular bundles, strands of xylem and phloem

12. Ground tissue system: tissues neither dermal nor vascular
includes cells specialized for storage, photosynthesis, and support
Pith: ground tissue internal to vascular tissue
Cortex: ground tissue external to vascular tissue

13. Common Types of Plant Cells
Plant characterized by cellular differentiation, the specialization of cells in structure and function
Plant cell types:
Parenchyma
Collenchyma
Sclerenchyma
Water-conducting cells of the xylem
Sugar-conducting cells of the phloem

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

15. Collenchyma Cells
Collenchyma cells: grouped in strands; help support young parts of plant shoot
have thicker and uneven cell walls
lack secondary walls
provide flexible support without restraining growth

16. Sclerenchyma Cells
Sclerenchyma cells: rigid because of thick secondary walls strengthened with lignin
dead at functional maturity
Two types:
Sclereids: short & irregular shape; thick lignified secondary walls
Fibers: long and slender; arranged in threads

17. Water Conducting Cells of Xylem
Two types of water- conducting cells:
BOTH DEAD at maturity
Tracheids: found in xylem of all vascular plants
Vessel elements: common to most angiosperms and few gymnosperms
align end to end to form long micropipes called vessels

18. Sugar-Conducting Cells of Phloem
Sieve-tube elements: alive at functional maturity, though lack organelles
Sieve plates: porous end walls that allow fluid to flow between cells along sieve tube
Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells

19. Concept 35.2: Meristems generate cells for new organs
Indeterminate growth: plant growth throughout its life
Determinate growth: some plant organs cease to grow at a certain size
Annuals: complete life cycle in a year or less
Biennials: require two growing seasons
Perennials: live for many years

20. Lateral meristems: add thickness to woody plants, AKA secondary growth
Meristems: perpetually embryonic tissue; allow for indeterminate growth
Apical meristems: located at tips of roots and shoots and at axillary buds of shoots
elongate shoots and roots, AKA primary growth
Lateral meristems: add thickness to woody plants, AKA secondary growth
two lateral meristems:
vascular cambium: adds layers of vascular tissue called secondary xylem (wood) and secondary phloem
cork cambium: replaces epidermis with periderm, which is thicker and tougher

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

22. Meristems give rise to:
initials: remain in meristem,
derivatives: become specialized in developing tissues
In woody plants, primary and secondary growth occur simultaneously but in different locations

23. Concept 35.3: Primary growth lengthens roots and shoots
Primary plant body: produced by primary growth; parts of root and shoot systems produced by apical meristems
Root cap: covers root tip; protects apical meristem as 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 maturation

24. Primary growth of roots produces:
epidermis
ground tissue
vascular tissue
In most roots, stele is vascular cylinder
Ground tissue fills cortex (region between vascular cylinder and epidermis)
Endodermis: innermost layer of the cortex is called the

25. Lateral roots arise from within pericycle
Fig
Lateral roots arise from within pericycle
outermost cell layer in vascular cylinder
100 µm
Epidermis
Emerging
lateral
root
Lateral root
Cortex
Figure The formation of a lateral root 1
Vascular
cylinder 2 3

26. Primary Growth of Shoots
Shoot apical meristem: dome- shaped mass of dividing cells at shoot tip
Leaves develop from leaf primordia along sides of apical meristem
Axillary buds develop from meristematic cells left at bases of leaf primordia

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

28. Tissue Organization of Leaves
Epidermis in leaves interrupted by stomata, which allow CO2 exchange between air and photosynthetic cells in leaf
Each stomatal pore is flanked by two guard cells, which regulate its opening and closing
Mesophyll: ground tissue in a leaf; sandwiched between the upper and lower epidermis
Spongy mesophyll: where gas exchange occurs; below palisade mesophyll in upper part of leaf
vascular tissue of each leaf is continuous with vascular tissue of the stem
Veins: leaf’s vascular bundles; function as leaf’s skeleton
Each vein enclosed by protective bundle sheath

29. Fig. 35-18 Figure 35.18 Leaf anatomy Guard cells Key to labels
Stomatal
pore
50 µm
Dermal
Epidermal
cell
Ground
Cuticle
Sclerenchyma
fibers
Vascular
Stoma
(b)
Surface view of a spiderwort
(Tradescantia) leaf (LM)
Upper
epidermis
Palisade
mesophyll
Bundle-
sheath
cell
Spongy
mesophyll
Figure Leaf anatomy
Lower
epidermis
100 µm
Cuticle
Xylem
Phloem
Vein
Guard
cells
Vein
Air spaces
Guard cells
(a) Cutaway drawing of leaf tissues
(c)
Cross section of a lilac
(Syringa)) leaf (LM)

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

31. Surface view of a spiderwort (Tradescantia) leaf (LM)
Fig b
Guard
cells
Stomatal
pore
50 µm
Epidermal
cell
Figure Leaf anatomy
(b)
Surface view of a spiderwort
(Tradescantia) leaf (LM)

32. Cross section of a lilac (Syringa) leaf (LM)
Fig c
Upper
epidermis
Key
to labels
Palisade
mesophyll
Dermal
Ground
Vascular
Spongy
mesophyll
Lower
epidermis
100 µm
Figure Leaf anatomy
Vein
Air spaces
Guard cells
(c)
Cross section of a lilac
(Syringa) leaf (LM)

33. Concept 35.4: Secondary growth adds girth to stems and roots in woody plants
Secondary growth occurs in stems and roots of woody plants but rarely in leaves
Secondary plant body: tissues produced by vascular cambium and cork cambium
characteristic of gymnosperms and many eudicots, but NOT monocots

34. Primary and secondary growth in a two-year-old stem Primary xylem
Fig a1
Pith
(a)
Primary and secondary growth
in a two-year-old 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 stem
Secondary phloem
Secondary
xylem

35. Primary and secondary growth in a two-year-old stem Primary xylem
Fig a2
Pith
(a)
Primary and secondary growth
in a two-year-old 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 stem
Secondary phloem
Secondary
xylem

36. Primary and secondary growth in a two-year-old stem Primary xylem
Fig a3
Pith
(a)
Primary and secondary growth
in a two-year-old 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)
Most recent cork
cambium
Figure Primary and secondary growth of a stem
Cork
Secondary phloem
Bark
Layers of
periderm
Secondary
xylem

37. Cross section of a three-year- old Tilia (linden) stem (LM)
Fig b
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 stem
Vascular ray
Growth ring
(b)
Cross section of a three-year-
old Tilia (linden) stem (LM)
0.5 mm

38. Vascular Cambium and Secondary Vascular Tissue
Vascular cambium: cylinder of meristematic cells one cell layer thick
develops from undifferentiated parenchyma cells
in cross section appears as a ring of initials
initials increase vascular cambium’s circumference and add secondary xylem to inside and secondary phloem to outside

39. Secondary xylem accumulates as wood, and consists of:
tracheids
vessel elements (only in angiosperms)
fibers
Early wood: formed in spring, has thin cell walls to maximize water delivery
Late wood: formed in late summer, has thick-walled cells and contributes more to stem support
In temperate regions, vascular cambium of perennials dormant through winter
Tree rings visible where late and early wood meet; can be used to estimate a tree’s age
Dendrochronology: analysis of tree ring growth patterns; can be used to study past climate change
What does this graph tell you?
Graph of Mongolian conifers: More growth=farther rings = warmer climate; Warmest climate from

40. As a tree or woody shrub ages, older layers of secondary xylem, AKA heartwood, no longer transport water and minerals
Outer layers, known as sapwood, still transport materials through the xylem
Older secondary phloem sloughs off and does not accumulate

41. Cork Cambium and Production of Periderm
Cork cambium: gives rise to secondary plant body’s protective covering, or periderm
Periderm consists of cork cambium plus layers of cork cells it produces
Bark: consists of all tissues external to vascular cambium, including secondary phloem and periderm
Lenticels: in periderm allow for gas exchange between living stem or root cells and outside air

42. Concept 35.5: Growth, morphogenesis, and differentiation produce the plant body
Morphogenesis: development of body form and organization
Three developmental processes act in concert to transform the fertilized egg into a plant:
growth
morphogenesis
cellular differentiation

43. Molecular Techniques Revolutionize the Study of Plants
Arabidopsis: model organism, and first plant to have its entire genome sequenced
Studying genes and biochemical pathways of Arabidopsis provide insights into plant development

44. Growth: Cell Division and Cell Expansion
By increasing cell number, cell division in meristems increases potential for growth
Cell expansion accounts for actual increase in plant size
Plane (direction) and symmetry of cell division are immensely important in determining plant form
If planes of division parallel to plane of first division, single file of cells is produced
If the planes of division vary randomly, asymmetrical cell division occurs

45. Plane in which cell divides determined during late interphase
Microtubules become concentrated into ring called preprophase band that predicts future plane of cell division

46. Orientation of Cell Expansion
Plant cells grow rapidly and “cheaply” by intake and storage of water in vacuoles AKA “Water Weight”
Plant cells expand primarily along plant’s main axis
Cellulose microfibrils in cell wall restrict direction of cell elongation

47. Morphogenesis and Pattern Formation
Pattern formation: development of specific structures in specific locations
controlled by homeotic genes
determined by positional information in form of signals indicating to each cell its location
may be provided by gradients of molecules
Polarity: having structural or chemical differences at opposite ends of organism, provides one type of positional information
Polarization initiated by asymmetrical first division of plant zygote
In gnom mutant of Arabidopsis, establishment of polarity is defective

48. Gene Expression and Control of Cellular Differentiation
Cellular differentiation depends on positional information and is affected by homeotic genes
Positional information underlies all processes of development: growth, morphogenesis, and differentiation
Cells NOT dedicated early to forming specific tissues and organs
Cell’s final position
determines what kind of cell it will become

49. Shifts in Development: Phase Changes
Phase changes: developmental phases from juvenile phase to adult phase
occur within shoot apical meristem
Most obvious morphological changes typically occur in leaf size and shape

50. Genetic Control of Flowering
Flower formation involves phase change from vegetative growth to reproductive growth
Triggered by combination of environmental cues and internal signals
Transition associated with switching on of floral meristem identity genes
Plant biologists identified several organ identity genes (plant homeotic genes) that regulate development of floral pattern
Mutation in plant organ identity gene  abnormal floral development

51. Researchers identified three classes of floral organ identity genes
ABC model of flower formation identifies how floral organ identity genes direct formation of four types of floral organs
Understanding mutants of organ identity genes depict how this model accounts for floral phenotypes

52. (a) A schematic diagram of the ABC hypothesis B C
Fig a
Sepals
Petals
Stamens A
Carpels
(a) A schematic diagram of the ABC hypothesis B C
C gene
activity
B + C
gene
activity
Carpel
A + B
gene
activity
Petal
Figure The ABC hypothesis for the functioning of organ identity genes in flower development
A gene
activity
Stamen
Sepal

53. (b) Side view of flowers with organ identity mutations
Fig b
Active
genes: B B B B B B B B A A A A A A C C C C A A C C C C C C C C A A C C C C A A A B B A A B B A
Whorls:
Carpel
Stamen
Petal
Figure The ABC hypothesis for the functioning of organ identity genes in flower development
Sepal
Wild type
Mutant lacking A
Mutant lacking B
Mutant lacking C
(b) Side view of flowers with organ identity mutations

54. You should now be able to:
Compare the following structures or cells:
Fibrous roots, taproots, root hairs, adventitious roots
Dermal, vascular, and ground tissues
Monocot leaves and eudicot leaves
Parenchyma, collenchyma, sclerenchyma, water-conducting cells of the xylem, and sugar-conducting cells of the phloem
Sieve-tube element and companion cell
Explain the phenomenon of apical dominance
Distinguish between determinate and indeterminate growth
Describe in detail the primary and secondary growth of the tissues of roots and shoots
Describe the composition of wood and bark
Distinguish between morphogenesis, differentiation, and growth
Explain how a vegetative shoot tip changes into a floral meristem

55. Explain the phenomenon of apical dominance
Distinguish between determinate and indeterminate growth
Describe in detail the primary and secondary growth of the tissues of roots and shoots
Describe the composition of wood and bark

56. Distinguish between morphogenesis, differentiation, and growth
Explain how a vegetative shoot tip changes into a floral meristem