2. 26.1 Organization of a Vascular Plant
Vascular plants have an outer covering of protective tissue & an inner matrix of vascular conductive tissue
A vascular plant is organized along a vertical axis
Root: The part belowground
Shoot: The part aboveground
Stem
Leaves
Sites of photosynthesis

3. Plants contain meristems, which are growth zones of unspecialized cells whose main function is to divide
Apical meristems
Responsible for primary growth
Results in elongation of the plant body
Lateral meristems
Responsible for secondary growth
Results in increase in thickness of the plant body
Vascular cambium
Gives rise to secondary xylem and phloem
Cork cambium
Gives rise to outer layer of bark

4. Fig The body of a plant

5. 26.2 Plant Tissue Types Most plants have three major tissue types
1. Ground tissue
Contains the vascular tissue
2. Dermal tissue
Outer protective layer
3. Vascular tissue
Conducts water, dissolved minerals and carbohydrates

6. Ground Tissue Makes up the main body of the plant
Contains several different cell types
Parenchyma cells
Fig. 26.2
Least specialized and most common
Alive at maturity
Carry out photosynthesis and storage functions
Have thin primary cell walls

7. Collenchyma cells Sclerenchyma cells Alive at maturity
Fig. 26.3
Alive at maturity
Uneven primary cell walls
Form strands & cylinders that provide support
Sclerenchyma cells
Dead at maturity
Thick secondary cell walls
Provide strength and rigidity
Fibers are long and slender
Sclereids are variable and branched
Fig. 26.4

8. Dermal Tissue
The epidermis of a plant is often covered with a thick waxy layer called the cuticle
Fig. 26.5
Guard cells
Paired cells with openings between them (stomata)
Allow gas exchange

9. Trichomes Root hairs Outgrowths of the epidermis, occurring on shoots
Fig. 26.5
Outgrowths of the epidermis, occurring on shoots
Variable in form
Regulate heat and water balance
Root hairs
Fig
Outgrowths of the epidermis, occurring on roots
Increase the surface area for absorption

10. Vascular Tissue Consists of xylem and phloem Xylem
Principal water-conducting tissue
Composed of tracheids and vessel elements
Both have thick secondary cell walls and are dead at maturity
Tracheids are connected by pits in their cell walls
Vessel elements are connected by perforations
A linked row of vessel elements forms a vessel

11. Fig. 26.6 Comparison of vessel elements and tracheids

12. Vascular Tissue Phloem Principal food-conducting tissue
Composed of sieve cells and sieve-tube members
Both are living, but lack nuclei at maturity
A linked row of sieve-tube members forms a sieve tube
Companion cells
Specialized cells found adjacent to sieve-tube members
Carry out metabolic functions needed to maintain sieve-tube members

13. Fig Sieve tubes

14. 26.3 Roots
Roots have a central column of xylem with radiating arms, alternating with strands of primary phloem
The pericycle is a layer of cells surrounding the vascular tissue
The endodermis lies outside the pericycle
It is encircled by a thickened waxy band, the Casparian strip
It controls the movement of water into the endodermis

15. There are three primary meristems Protoderm: produces the epidermis
Procambium: produces the vascular tissue
Ground meristem: produces the ground tissue
The root cap covers & protects the apical meristem
Zone of elongation
Newly-formed cells are elongating, causing the root to reach further into the soil
Zone of differentiation
Cells are taking on specialized forms and functions
Example: Root hairs

16. Fig Root structure

17. In stems, branching originates at the surface
A fundamental difference between roots and shoots has to do with branching
Fig Lateral roots
In stems, branching originates at the surface
In roots, branching originates below the surface

18. 26.4 Stems Stems serve two purposes Main structural support for plant
Famework for positioning the leaves
Stems often experience two types of growth
Primary growth
Secondary growth

19. Primary Growth
Leaves cluster around apical meristem, unfolding and growing as the stem elongates
Fig A woody twig
Leaves grow out of stems at the nodes
Buds develop in the axil of each leaf
A terminal bud hormone continuously suppresses expansion of lateral buds

20. The arrangement of vascular tissue in stems differs
In dicots, the vascular bundles are arranged around the outside of the stem
In monocots, the vascular bundles are scattered throughout the stem
Pith = Inner portion of ground tissue
Fig
Cortex = Outer portion of ground tissue

21. Secondary Growth Results from the differentiation of lateral meristems
Vascular cambium and cork cambium
The vascular cambium develops from a thin cell layer located between the primary xylem and phloem
It divides outwardly to produce the secondary phloem
Inward division results in the secondary xylem
The cork cambium develops in the stem’s outer layer
Outwardly, it splits off densely packed cork cells
Inwardly, it divides to produce a layer of parenchyma cells

22. Fig. 26.13 Vascular cambium and secondary growth

23. Bark refers to all of the tissues outside the vascular cambium
Wood, anatomically-speaking, is accumulated secondary xylem
Fig Annual rings in pine
Because of the way it is accumulated, wood often displays rings
In temperate regions, these rings are annual rings

24. 26.5 Leaves Leaves are outgrowths of the shoot apex
They are the major light-capturing organs of most plants
Leaves grow outward by marginal meristems
This ultimately forms the blade (flattened portion)
Most leaves also have
A petiole – slender stalk
Stipules – leaflike organs flanking the petiole

25. Veins (xylem and phloem) run through leaves
Most dicots have leaves with netted or reticulate veins
Most monocots have leaves with parallel veins
Fig

26. Leaf blades come in different forms
Fig a
Simple leaves have a single undivided blade
Compound leaves have blades divided into leaflets
Pinnately compound leaves
Leaflets arranged in pairs along a common axis
Palmately compound leaves
Leaflets radiate out from a common point
Fig c
Fig d

27. Circle of leaves at the same node level
There are three common types of leaf arrangements
Alternate
Opposite
Whorled
Two leaves per node
Circle of leaves at the same node level
Fig
One leaf per node

28. A leaf consists of parenchyma tissue called mesophyll
Two types: palisade and spongy
Fig A leaf in cross section
Allow passage of CO2

29. 26.6 Water Movement
Plants use chains of specialized cells to carry out transport function
Phloem transports photosynthetically-produced carbohydrates up and down the plant
Xylem transports water and minerals upward
But how can water be moved up to the height of a plant?

30. Cohesion-Adhesion-Tension Theory
The initial movement of water into the roots of a plant involves osmosis
Fig
This root pressure provides a “push”
The narrower the tube, the higher the water rises
Capillary action adds a “pull”
This is a result of adhesion

31. Transpiration provides a second very strong “pull”
Passage of air across leaf surfaces results in loss of water by evaporation
This creates a “pull” at the open upper end of the plant
Water molecules entering the roots are pulled up
Water molecules undergo cohesion because of their tendency to form hydrogen bonds with one another
Thus, a column of water resists separation
This resistance is called tensile strength
It varies inversely with the column diameter

32. Transpiration The process by which water leaves the plant
> 90% of water taken in by roots is lost to the atmosphere
Fig

33. Transpiration Factors affecting evaporation also affect transpiration
Humidity levels
High humidity reduces evaporation
Low humidity increases it
Temperature
High temperature increases evaporation
Low humidity decreases it

34. Regulation of Transpiration
Plants control short-term water loss by closing stomata
But the stomata must be opened to obtain CO2
The stomata open and close because of changes in water pressure of their guard cells
Water entering guard cells causes them to bow outward
This opens the stomata
Water leaving guard cells causes them to wilt
This closes the stomata

35. Guard cells turgid
Guard cells flaccid
Fig

36. Water Absorption by Roots
Most of the water absorbed by plants comes in through root hairs
Fig
Root hairs are greatly reduced in number in plants with ectomycorrhizae
Fungal filaments take their place in promoting absorption
Minerals also enter the root through root hairs
These are transported to the rest of the plant via the xylem

37. Fig. 26.23 The transport of materials into, out of, and within a plant

38. 26.7 Carbohydrate Transport
Carbohydrates manufactured in plant leaves is moved through the phloem to other parts of the plant
This process is known as translocation
It does not require energy
The mass flow of materials occurs because of water pressure
Water pressure develops as a result of osmosis

39. Fig. 26.24 How translocation works

40. 26.8 Essential Nutrients Plants require many nutrients Nitrogen (N)
Part of proteins and nucleic acids
Potassium (K)
Regulates turgor pressure
Calcium (Ca)
Part of middle lamellae
Magnesium (Mg)
Part of the chlorophyll molecule
Phosphorus (P)
Part of nucleic acids and ATP

41. Most plants acquire nutrients from the soil
However, carnivorous plants use other organisms directly as nutrient sources
Asian pitcher plant
Fig
Venus’s-flytrap