1. Lecture 9 Outline (Ch. 35) Overview of plant systems
Major plant cell types
Three plant tissues
Three plant organs
Plant growth
Meristems
Primary vs secondary
Cell elongation & division
VI. Summary

2. Plant Structure, Growth, Development
Plants are notably different from animals:
SA:V ratio
Mobility
Growth
Response to environment
Cell structure

3. Cells  Tissues  Organs  Systems
Setting the scene - animal bodies
Cells  Tissues  Organs  Systems

4. Plant Cell Types Plant cell structure recap Cell wall, plasmodesmata
Primary wall (some have secondary wall), middle lamella

5. Plant Cell Types 1) Parenchyma (most abundant):
Flexible, thin-walled cells; living
plant metabolism:
Photosynthesis; hormone secretion; sugar storage
Parenchyma cells in
Elodea leaf,(w/chloroplasts)
thin wall permeable to gasses
large central vacuole
able to divide and differentiate

6. Plant Cell Types 2) Collenchyma: Able to elongate
Thick-walled (uneven); living
Offers support (flexible & strong)
Able to elongate
Grouped in strands, lack secondary wall
Collenchyma cells sunflower

7. Plant Cell Types 3) Sclerenchyma: Thick, hard-walled; Dead
Offer support (e.g. hemp fibers; nut shells)
Thick secondary walls with lignin
Rigid (cannot elongate)
Two types – sclereids and fibers
Sclereid cells
in pear (LM)
Fiber cells in ash tree
Cell wall

8. Plant Tissue Systems 1) Dermal Tissues Outer covering Protection
2) Vascular Tissues
“Vessels” throughout plant
Transport materials
3) Ground Tissues
“Body” of plant
Photosynthesis; storage; support
Made mostly of basic cell types:
Parenchyma
Collenchyma
Sclerenchyma

9. Three Basic Plant Organs: Roots, Stems, and Leaves
Plant “bodies”
Dermal
tissue
Ground
Vascular
Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells
Each plant organ has dermal, vascular, and ground tissue systems
Three Basic Plant Organs: Roots, Stems, and Leaves

10. Think about plant “bodies” in comparison to animal bodies:
For humans list example:
CELL TYPES
TISSUES
ORGANS
B. For plants list:
3 CELL TYPES
3 TISSUE SYSTEMS
3 ORGANS

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

12. Plant Tissues - Dermis Special Dermal Cells – Trichomes & Root hairs
Hair-like outgrowths of epidermis
Keep leaf surfaces cool and reduce evaporation
Roots hairs
Tube extensions from epidermal cells
Greatly increase the root’s surface area for absorption

13. Plant Tissues - Dermis Special Dermal Cells – Guard Cells
Stomata
Stomata
Guard cells
Guard cells
Epidermal cell
Epidermal cell a. c.
4 µm
200 µm
Paired sausage-shaped cells
Flank a stoma – epidermal opening
Passageway for oxygen, carbon dioxide, and water vapor
Stoma
Stoma
Epidermal cell
Epidermal cell
Guard cells
Guard cells b.
71 µm

14. Plant Tissues - Vascular
Vascular tissues made up of multiple cell types:
Arranged in multiple bundles or central cylinder
Xylem – water and nutrients
Phloem – dissolved sugars and metabolites

15. Plant Tissues - Vascular
1) Xylem (dead at maturity): water and minerals roots to shoots
Tracheids: Narrow, tube-like cells
Vessel Elements: Wide, tube-like cells
Fibers

16. Plant Tissues - Vascular
1) Xylem:
Tracheids:
- Most vascular plants
- Long, thin, tapered ends, lignified secondary walls
- Water moves cell to cell through pits
Vessel elements:
- Wider and shorter
- Perforation plates ends of vessel elements
- water flows freely though perforation plates

17. Plant Tissues - Vascular
Sieve Tubes: Wide, tube-like cells
B) Companion Cells: support and regulate sieve tubes
2) Phloem (living at maturity) cells:

18. Plant Tissues - Vascular
2) Phloem (living at maturity)
- Moves water, sugar, amino acids & hormones
Sieve tube elements/members
• Long narrow cells stack end to end
• Pores in end walls (sieve plates)
• Lack most cellular structures including:
distinct vacuole, Some cytoskeletal elements, Nucleus, Ribosomes
Companion Cells:
• Adjacent to every sieve tube element
• Non-conducting.
• Regulate both cells
• Connected by numerous plasmodesmata

19. Plant Tissues – Ground Tissue
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
Includes parenchyma, collenchyma, sclerenchyma

20. Plant Organs: 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

21. Plant Organs: Roots - Comparisons
Taproots:
Fibrous roots:
Typical of dicots, primary root forms and small branch roots grow from it
In monocots mostly, primary root dies, replaced by new roots from stem

22. Plant Organs: Roots – Structure and Development
Four regions:
Root cap
Protection, gravity detection
Zone of cell division
Mitotic divisions
Zone of elongation
Cells lengthen, no division
Zone of maturation
Cells differentiate, outer layer becomes dermis

23. Plant Organs: Roots – Vasculature
Epidermis
Cortex
Endodermis
Vascular cylinder
Pericycle
Core of parenchyma cells
Xylem
Phloem
Dermal
Ground
Vascular
Key to labels
50 m
100 m
(a)
(b)
Root with parenchyma in the center
Root with xylem and phloem in the center
Dicot
Monocot

24. 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
Water storage

25. Plant Organs: Stems - Overview
Apical bud
Node
Internode
Apical
bud
Shoot
system
Vegetative
shoot
Axillary
Stem
Stem: an organ made of
Alternating nodes, points of leaf attachment
Internodes, stem length between nodes
Axillary bud - can form a lateral shoot/branch
Apical (terminal) bud - near the shoot tip, lengthens a shoot
Apical dominance maintains dormancy in most non-apical buds

26. Vasculature - 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
Dicot Monocot

27. Stems – Many Plants Have Modified Stems
Rhizomes
Bulbs
Storage leaves
Stem
Stolons
Stolon
Tubers

28. So far we have covered the organs stems and roots:
Match each term number with a letter for the image: A. B.
Monocot stem
Monocot root
Dicot stem
Dicot root C. D.

29. Plant Organs: 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 - joins the leaf to node of the stem

30. Leaves – Structure
Leaves are several layers thick – different cell types
Key to labels
Dermal
Ground
Vascular
Cuticle
Xylem
Phloem
Sclerenchyma fibers
Stoma
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis
Vein
Guard cells

31. Plant Organs: Leaves
Leaf epidermis contains stomata - allow CO2 exchange
Stomata flanked by two guard cells, control open vs. closed

32. Plant Organs: 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

33. Leaves – Plants have modified leaves for various functions
Tendrils
Spines
Storage
leaves
Reproductive leaves
Bracts

34. Plant Classification – Monocots vs. Dicots
Basic categories of plants based on structure and function

35. 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

36. 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

37. Plant Growth – primary growth

38. Plant Growth in woody plants (secondary growth)
Two lateral meristems: vascular cambium and cork cambium
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
thicker, stronger stems
Vascular Cambium: between primary xylem and phloem

39. Plant Growth Stem – Secondary Growth: Produces inside stem:
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular ray
Growth
Secondary xylem
Secondary phloem
First cork cambium
Cork
Produces inside stem:
A) Secondary xylem
moves H2O, inward
B) Secondary phloem
moves sugars, outward

40. Plant Growth Vascular Cambium: Pith Primary xylem Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular ray
Growth
Secondary xylem
Secondary phloem
First cork cambium
Cork
Bark
Most recent cork cambium
Layers of periderm

41. A hammock is hung between two trees in his backyard by a young man who is 15 years old.
If he returns 20 years later to find his hammock, how will the position of the hammock have changed?

42. Plant Growth – cell growth
Plant cells have cellulose microfibrils in the cell wall
These can be enzymatically loosened, and the cell expanded by storing water in the central vacuole. Later the fibrils reattach.

43. Plant Growth – asymmetric divisions
Often plant cells divide unequally in specifying cell types.
For example, to form guard cells of stomata, the first division is toward one end of the cell. The second division is rotated 90 degrees.
Two guard cells
Unspecialized epidermal cell