2. Lecture 8 Outline (Ch. 35) Plant organs Plant tissues
A. Roots
B. Stems
C. Leaves
Plant tissues
A. Dermal
B. Vascular
C. Ground
III. Plant Growth
A. Meristems
B. Primary vs. secondary
IV. Lecture Concepts

3. Three Basic Plant Organs: Roots, Stems, and Leaves
Plant “bodies”
Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells
Shoot
system
Leaf
Stem
Three Basic Plant Organs: Roots, Stems, and Leaves
Root
system

4. Roots - Overview Roots need sugars from photosynthesis;
Shoots rely on water and minerals absorbed by the root system
Root Roles:
- Anchoring the plant
- Absorbing minerals and water
- Storing organic nutrients

5. Roots - Comparisons Taproots: Fibrous roots:
FIGURE Typical root systems in dicots and monocots
(a) Dicots typically have a taproot system, consisting of a long central root with many smaller, secondary roots branching from it. (b) Monocots usually have a fibrous root system, with many roots of equal size.
Typical of dicots, a primary root forms and small branch roots grow from it
In monocots and seedless vascular plants, the primary root dies, replaced by new roots from stem

6. Roots – Many Plants Have Modified Roots
Prop roots
“Strangling”
aerial roots
Storage roots
Buttress roots
Pneumatophores
Roots – Many Plants Have Modified Roots
Figure 35.4 Modified roots

7. Stems - Overview Stem: an organ made of
Apical bud
Node
Internode
Apical
bud
Shoot
system
Vegetative
shoot
Axillary
Stem
Stem: an organ made of
An alternating system of nodes, points at which leaves attach
Internodes, stem length between nodes
Axillary bud - structure that can form a lateral shoot, or branch
Apical/terminal bud - located near the shoot tip, lengthens a shoot
Apical dominance maintains dormancy in most nonapical buds

8. Stems – Many Plants Have Modified Stems
Rhizomes
Bulbs
Storage leaves
Stem
Stolons
Stolon
Tubers
Figure 35.5 Modified stems

9. Leaves - Overview
Shoot
system
Leaf
Blade
Petiole
The leaf is the main photosynthetic organ of most vascular plants
Leaves generally have
a flattened blade
and a stalk called the petiole, which joins the leaf to a node of the stem

10. Leaves - Comparisons
Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves
Most dicots have branch-like veins and palmate leaf shape
Monocots have parallel leaf veins and longer, slender blades

11. Leaves – Plants have modified leaves for various functions
Tendrils
Spines
Storage
leaves
Figure 35.7 Modified leaves
Reproductive leaves
Bracts

12. Plant Tissues
Dermal
tissue
Ground
Vascular
Each plant organ has dermal, vascular, and ground tissues
Each of these three categories forms a tissue system

13. Plant Tissues 1) Dermal Tissue System Outer covering Protection
2) Vascular Tissue System
“Vessels” throughout plant
Transport materials
3) Ground Tissue System
“Body” of plant
Photosynthesis; storage; support

14. Plant Tissues - Dermis Dermal Tissue System (Outer Covering of Plant):
1) Epidermal Tissue (epidermis):
Forms outermost layer
Cuticle: Waxy covering
Reduces evaporation
Inhibits microorganism invasion
Root Hairs: extended root surface
Increase absorption
2) Peridermal Tissue (periderm):
Only in woody plants (“bark = dead cells”)
Protection; support

15. Plant Tissues - Dermis

16. Plant Tissues - Vascular
Vascular Transport System
1) Xylem (dead at maturity):
- Moves water & minerals from roots to shoots

17. Plant Tissues - Vascular
Vascular Transport System
2) Phloem (living at maturity)
- Moves water, sugar, amino acids & hormones

18. Vasculature - Comparisons
Monocots and dicots differ in the arrangement of vessels in the roots and stems
Dicots
Monocots
Stem
Root

19. Plant Tissues – Ground Tissue
Some major types of plant cells:
Parenchyma
Collenchyma
Sclerenchyma
Water-conducting cells of the xylem
Sugar-conducting cells of the phloem
Tissues that are neither dermal nor vascular are ground tissue
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

20. Plant Tissues - Ground Ground Tissue System (“Body” of Plant):
1) Parenchyma (most abundant):
Thin-walled cells; living
plant metabolism:
Photosynthesis; hormone secretion; sugar storage
FIGURE 42-5 The structure of ground tissue
(a) Parenchyma cells are living and serve many functions. They have thin, flexible primary cell walls. These parenchyma cells are used for starch storage in a potato. (b) Collenchyma cells are living and have thickened, but somewhat flexible, primary walls. They help support the plant body (as seen in this celery stalk). (c) Sclerenchyma cells have thick, rigid secondary cell walls and die after they differentiate. Illustrated are "stone cells" that give pear fruit its slightly gritty texture.
Parenchyma cells in
Elodea leaf,(w/chloroplasts)

21. Plant Tissues - Ground Ground Tissue System (“Body” of Plant):
2) Collenchyma:
Thick-walled (uneven); living
Offers support (flexible & strong)
FIGURE 42-5 The structure of ground tissue
(a) Parenchyma cells are living and serve many functions. They have thin, flexible primary cell walls. These parenchyma cells are used for starch storage in a potato. (b) Collenchyma cells are living and have thickened, but somewhat flexible, primary walls. They help support the plant body (as seen in this celery stalk). (c) Sclerenchyma cells have thick, rigid secondary cell walls and die after they differentiate. Illustrated are "stone cells" that give pear fruit its slightly gritty texture.
Collenchyma cells sunflower

22. Plant Tissues - Ground Ground Tissue System (“Body” of Plant):
Sclereid cells in pear (LM)
Fiber cells in ash tree
Cell wall
3) Sclerenchyma:
Thick, hard-walled; Dead
Offer support (e.g. hemp fibers; nut shells)
FIGURE 42-5 The structure of ground tissue
(a) Parenchyma cells are living and serve many functions. They have thin, flexible primary cell walls. These parenchyma cells are used for starch storage in a potato. (b) Collenchyma cells are living and have thickened, but somewhat flexible, primary walls. They help support the plant body (as seen in this celery stalk). (c) Sclerenchyma cells have thick, rigid secondary cell walls and die after they differentiate. Illustrated are "stone cells" that give pear fruit its slightly gritty texture.

23. Plant Tissues - Vascular
1) Xylem (dead at maturity):
Tracheids: Narrow, tube-like cells
Vessel Elements: Wide, tube-like cells
Perforation
plate
Vessel
element
Vessel elements, with
perforated end walls
Tracheids
Pits
Tracheids and vessels
100 µm

24. Plant Tissues - Vascular
Sieve Tubes: Wide, tube-like cells
B) Companion Cells: support and regulate sieve tubes
2) Phloem (living at maturity)
Sieve-tube element (left)
and companion cell:
cross section
3 µm
Sieve-tube elements:
longitudinal view
Sieve plate
Companion
cells
Sieve-tube
elements
Plasmodesma
Sieve
plate
Nucleus of
companion
Sieve plate with pores
10 µm
30 µm

25. Plant Growth Plant Growth: 1) Indeterminate: Grow throughout life
2) Growth at “tips” (length) and at “hips” (girth)
Growth patterns in plant:
1) Meristem Cells: Dividing Cells
2) Differentiated Cells: Cells specialized in structure & role
Form stable, permanent part of plant

26. Plant Growth 1) Primary Growth: Apical Meristems:
girth
length
1) Primary Growth:
Apical Meristems:
Mitotic cells at “tips” of roots / stems
1) Increased length
2) Specialized structures (e.g. fruits)
2) Secondary Growth:
Lateral Meristems: Mitotic cells “hips” of plant
Responsible for increases in stem/root diameter

27. Plant Growth Shoot apical meristem Leaf primordia Young leaf
Developing
vascular
strand
Figure The shoot tip
Axillary bud
meristems

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

29. Plant Growth Stem – Secondary Growth: thicker, stronger stems
primary phloem
thicker, stronger stems
Vascular Cambium: between primary xylem and phloem
vascular cambium
primary xylem
epidermis
Produces inside stem:
pith
A) Secondary xylem
moves H2O, inward
B) Secondary phloem
moves sugars, outward
cortex
primary xylem
dividing
vascular
cambium
primary phloem

30. Plant Growth Vascular Cambium: Secondary growth primary phloem
dividing
vascular
cambium
new
secondary
xylem
secondary phloem
primary phloem
vascular cambium
primary xylem
secondary xylem
pith
cortex
Secondary growth
Vascular cambium
Growth
Secondary
xylem
After one year
of growth
After two years
phloem
Vascular
cambium X P C

31. Plant Growth Stem – Secondary Growth: Cork Cambium:
ring
Vascular
ray
Secondary
xylem
Heartwood
Sapwood
Bark
Vascular cambium
Secondary phloem
Layers of periderm
Located under outer surface; produces periderm
Dead at maturity
Protection

32. Plant Growth Stem – Secondary Growth: heartwood (xylem) sapwood
vascular
cambium
phloem
annual ring
Sapwood = Young xylem, water
Heartwood = Old xylem, support
Seasonal Growth = annual rings
Secondary phloem = grows outward older phloem crushed
FIGURE How annual tree rings are formed
(a) Tree rings are clearly visible in this section of tree trunk. The ratio of cell wall to "hole" (the now-empty interior of the cell) determines the color of the wood: early wood, formed during the spring, with lots of hole, is pale; late wood, formed during the summer, with lots of wall, is dark. The water-transporting xylem of sapwood forms a lighter layer inside the bark. Xylem of the older heartwood, where the rings are most easily visible, no longer transports water and minerals. (b) As this micrograph shows, secondary xylem cells formed during the wet spring are large (early xylem), whereas secondary xylem cells formed during the hotter, drier summer are small (late xylem).
late
xylem
early
xylem

33. Plant Growth RESULTS 2 1.5 Ring-width indexes 1 0.5 1600 1700 1800
Figure 35.21
1600
1700
1800
1900
2000
Year
Using dendrochronology to study climate

34. Plant Growth Living tree or dead tree?
Figure Is this tree living or dead?

35. Plant Growth - Roots
Epidermis
Cortex
Endodermis
Vascular
cylinder
Pericycle
Core of
parenchyma
cells
Xylem
Phloem
100 µm
Root with xylem and phloem in the center
(typical of eudicots)
(a)
Root with parenchyma in the center (typical of
monocots)
(b)
Key
to labels
Dermal
Ground
Figure Organization of primary tissues in young roots

36. Plant Growth - Stems
In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring
Phloem
Xylem
Sclerenchyma
(fiber cells)
Ground tissue
connecting
pith to cortex
Pith
Cortex
1 mm
Epidermis
Vascular
bundle
Cross section of stem with vascular bundles forming
a ring (typical of eudicots)
(a)
Key
to labels
Dermal
Ground
Cross section of stem with scattered vascular bundles
(typical of monocots)
(b)
bundles
tissue
Figure Organization of primary tissues in young stems

37. Plant Growth - Leaves
Leaf epidermis contains stomata - allow CO2 exchange
Stomata flanked by two guard cells, control open vs. closed
The ground tissue in a leaf, called mesophyll, fills the middle
Key
to labels
Dermal
Ground
Vascular
Cuticle
Sclerenchyma
fibers
Stoma
Bundle-
sheath
cell
Xylem
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Vein
Lower
epidermis
Spongy
mesophyll
Palisade
Upper
Stomatal
pore
Surface view of a spiderwort
(Tradescantia) leaf (LM)
Epidermal
(b)
50 µm
100 µm
Air spaces
Guard cells
Cross section of a lilac
(Syringa)) leaf (LM)
(c)
Figure Organization of primary tissues in young stems

38. Lecture 8 Concepts
Compare monocots and dicots in terms on vasculature in stems, leaves and roots, leaf shape, root type.
Describe dermal, vascular, and ground tissues
List the roles for roots, stems, leaves.
Compare xylem versus phloem – function, location, growth.
Discuss differences between parenchyma, collenchyma, sclerenchyma cells.
Describe primary versus secondary growth.
Explain what ‘bark’ is made out of – is it essential for the tree?
Write out a list of new terminology and provide descriptions