1. PLANT STRUCTURE AND GROWTH
CHAPTER 35
PLANT STRUCTURE AND GROWTH

2. Plants are the first link in the food chain through. photosynthesis
Plants are the first link in the food chain through photosynthesis. This affects all animals.
I. Concept 35.1: Plant Structure
Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells
A. Three Basic Plant Organs: Roots, Stems, Leaves
They are organized into a root system and a shoot system
Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system

4. 1. Roots
Are multicellular organs with important functions:
Anchoring the plant
Absorbing minerals and water
Storing organic nutrients
A 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 a fibrous root system characterized by thin lateral roots with no main root

5. 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 modified roots

7. 2. Stems
A stem is an organ consisting of:
An alternating system of nodes, the points at which leaves are attached
b. 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
Apical dominance helps to maintain dormancy in most nonapical buds
Many plants have modified stems

8. Modified stems include:
Stolons—horizontal stems growing along surface of ground (strawberry)
Rhizomes—horizontal stems growing underground (iris)
Tubers—some end in enlarged tubes where food is stored (potatoes)
Bulbs—vertical, underground shoots with leaves modified for food storage (onion)

10. 3. Leaves a. Are the main photosynthetic organ of most vascular plants b. Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem c. Some plant species have evolved modified leaves that serve various functions

11. Types of Leaves

12. MODIFIED LEAVES

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

15. 1. Dermal Tissue System
Outer protective covering that secretes the cuticle
In nonwoody plants consists of the epidermis
In woody plants periderm replaces the epidermis in older regions of stems and roots

16. 2. Vascular Tissue System
Carries out long-distance transport of material between roots and shoots
Two types of Vascular Tissue:
a. xylem-transports water and dissolved mineral upward from root into shoots
b. phloem-transports organic nutrients from where they are made to where they are needed
Vascular tissue of a stem or root is collectively called the stele
The stele of stems and leaves is divided into vascular bundles (strands of xylem and phloem)

17. Ground Tissue System
Refers to any tissue not dermal or vascular
Include cells specialized for photosynthesis, storage
and support

18. C. Common Types of Plant Cells
Parenchyma
Collenchyme
Sclerenchyma
Water–conducting cells of the xylem
Sugar—conducting cells of phloem

19. Protoplast—refers to cell contents exclusive of the cell wall
1. Parenchyma Cells
Most abundant plant tissue
Primary walls are thin and flexible
Lack secondary walls
Store food and water
Protoplast has large central vacuole
Perform most of plant’s metabolic functions such as PS and food storage
Least specialized—typical plant cell
Retains the ability to divide and differentiate into other cell types under special conditions (wound healing)

20. Parenchyma Cells

21. 2. Collenchyma
Living support tissue with unevenly thickened cell walls
No secondary walls (no lignin)
Usually grouped in strands or cylinders for support for young parts of plant
Located just beneath the epidermis and along the midrib of a leaf
Provide flexible support

22. Collenchyma Cells

23. Parenchyma and Collenchyma Cells

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

25. Sclereid and Fiber Cells

26. Sclerenchyma

27. 4. Xylem
Water conducting cells
Dead cells with secondary walls
Stain red
Consists of two cell types:
a. Tracheids
-long, thin, tapered cells with lignin-hardened secondary walls with pits
-water moves from cell to cell through pits
-function in support and water transport
-more primitive
-found in xylem of all vascular plants

28. b. Vessel elements -wider, shorter, thinner-walled -less tapered
-long chains of vessel elements called xylem vessels
-more efficient water conductors than tracheids
-more advanced
-found in most angiosperms and a few
gymnosperms

29. XYLEM

30. 5. Phloem Sugar-conducting cells Stain green
Alive at functional maturity
Composed of:
a. Sieve tube elements
-long narrow cells
-lack nucleus, ribosomes, and vacuole, but are alive at maturity
-sieve plates (end walls) are perforated as well as side walls
b. Companion cells
-lie adjacent to sieve tubes and direct their activity
-connected to sieve tube by plasmodesmata (thin streams of cytoplasm)

31. Phloem

32. Xylem and Phloem

33. II. Concept 35.2: Meristematic Tissues
A. A plant can grow throughout its life; this is called indeterminate growth
B. Some plant organs cease to grow at a certain size; this is called determinate growth
C. Life span of flowering plants:
Annuals complete their life cycle in a year or less
Biennials require two growing seasons
Perennials live for many years

34. D. 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
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

37. III. Concept 35.3: Primary growth lengthens roots and shoots
Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems
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
Near tip and includes the apical meristem
Quiescent center is made up of reserve replacement cells

38. 2. Zone of elongation
Cells elongate and push root through the soil
3. Zone of differentiation
Elongated cells complete their differentiation and become functionally mature
Region where root hairs develop
Farthest from root tip

40. The primary growth of roots produces the epidermis, ground tissue, and vascular tissue
In most roots, the stele is a vascular cylinder
The ground tissue fills the cortex, the region between the vascular cylinder and epidermis
The innermost layer of the cortex is called the endodermis
Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder

41. Eudicot Root

42. Stele—Vascular Cylinder

43. Monocot Root

44. Lateral Roots

47. B. 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

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

50. Stems

51. 2. Tissue Organization of Leaves
The epidermis in leaves is interrupted by stomata, which allow CO2 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
Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll, where gas exchange occurs

52. 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

53. Leaves

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

55. Secondary Growth

57. D. The Cork Cambium and the Production of Periderm
The cork cambium gives rise to the secondary plant body’s protective covering, or periderm
Periderm consists of the cork cambium plus the layers of cork cells it produces
Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm