1. Chapter 9: Plant Organization
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2. Plant Organs
The flowering plants, or angiosperms, have characteristic organs and tissues.
An organ is a structure that contains different types of tissues and performs one or more specific functions.
Flowering plants are extremely diverse because they are adapted to living in varied environments. Despite their great diversity in size and shape, flowering plants usually have three vegetative organs – roots, stems, and leaves.

3. Organization of the plant body
Fig. 9.1
Vegetative organs are the leaf, stem and root
The body of a plant has a root system and a shoot system.
Shoot System
The body of a plant consists of a root system and a shoot system. Roots are the only type of plant organ in the root system. The shoot system contains stems and leaves, two other types of plant organs. The root system is connected to the shoot system by vascular tissues that extends from the roots to the leaves. Axillary buds can develop into branches of stems or flowers, the reproductive structures of a plant.
Root System

4. The Root System Consists of a main root (taproot) and many lateral
roots, which absorb water
and minerals from the soil
for the plant.
The absorptive capacity of a root is greatly increased by its many root hairs located in a special zone near the root tip. Root hairs, which are projections from root-hair cells, are especially responsible for the absorption of water and minerals. Root hairs are so numerous that they increase the absorptive capacity of a root tremendously. Root-hair cells are constantly being replaced.

5. Root systems -Produce hormones
Fig. 9.2
-Produce hormones
-Perennial plants often store the products of photosynthesis in their roots.
The root system anchors the plant and absorbs water and minerals.

6. Shoot System - Stems
Fig. 9.1
A stem is the main axis of the plant along with its lateral branches.
Transports water and minerals from roots to leaves, and products of photosynthesis in the other direction.
A cylindrical stem can expand in girth as well as in length.

7. Shoot System - Leaves
A leaf is a broad, thin organ (maximizes surface area) that carries on photosynthesis (some have other functions).
Fig. 9.1
A leaf attaches to a stem at a node; an internode is the region beween nodes.

8. Blade
Petiole
Attaches to the node here

9. Monocot Versus Dicot Plants
Flowering plants are divided into two groups depending on their number of cotyledons (seed leaves).
Monocots (monocotyledons) have one cotyledon; dicots (dicotyledons) have two.
Cotyledons provide nutrients for seedlings before true leaves begin photosynthesizing.

10. Monocot and dicot traits
Fig. 9.3
The number of cotyledons, and the arrangement of vascular tissue in roots and stems distinguishes monocots from dicots.

11. Monocots: Dicots: Parallel veins (sugarcane, corn)
Fig. 9.3
Monocots:
Parallel veins (sugarcane, corn)
Flowers have 3 or multiples of 3 (6,9,12, etc.) parts
Dicots:
Veins form a net pattern (oak tree)
Flowers have 4 or 5 or multiples of 4 or 5 (8,10, etc.) parts
Monocots and dicots differ in the venation pattern of leaves and in number of flower parts.

12. Dicot leaves
From Page 150

13. Plant Tissues Epidermal tissue – outer covering
Ground tissue – majority of plant tissue
Vascular tissue – transport
Three types of meristem continually produce three types of specialized tissue in the body of the plant: protoderm, the outermost primary meristem gives rise to epidermis; ground meristem produces ground tissue; and procambium produces vascular tissue.

14. Epidermal Tissue
Epidermal tissue forms the outer protective covering of a herbaceous (non-woody) plant.
Exposed epidermal cells are covered with waxy cuticle to minimize water loss.
Root hairs increase the surface area of a root for absorption of water and minerals and help anchor the plant firmly in place.
Protective hairs of a different nature are produced by epidermal cells of stems and leaves. Epidermal cells may also be modified as glands that secrete protective substances of various types.
In leaves, the lower epidermis in particular contains specialized cells called guard cells. The guard cells, which unlike epidermal cells have chloroplasts, surround microscopic pores called stomata (sing., stoma). When the stomata are open, gas exchange occurs.

15. Root Hairs are Epidermal Tissue
Fig. 9.4
Root hairs greatly increase the absorptive capacity of the root.
Epidermal modifications include root hairs to absorb water.

16. Stoma of leaves are part of the epidermal tissue
Fig. 9.4
Epidermal modifications include stomata in leaf epidermis that functions in gas exchange. The stoma (pore) is opened or closed by guard cells.

17. Cork (an epidermal tissue) of an older stem
Fig. 9.4
Cork is a component of bark.
New cork cells are made by a meristem called cork cambium.
As cork cells mature, they fill with suberin, a lipid that makes them waterproof and chemically inert.
Cork replaces epidermis in older woody stems.

18. Ground Tissue -forms the bulk of the plant.
Fig. 9.5
Parenchyma cells have thin walls and intercellular air spaces. The walls of collenchyma cells are much thicker than those of parenchyma cells. Sclerenchyma cells have very thick walls and are nonliving – their only function is to give strong support.
-are hollow, nonliving support cells with secondary walls.
-thin-walled and capable of photosynthesis when they contain chloroplasts.
-have thicker walls for flexible support (celery strands).

19. Vascular Tissue Two types of vascular (transport) tissue:
Xylem transports water and minerals from roots to leaves and contains two types of conducting cells: tracheids and vessel elements.
Phloem transports organic nutrients from leaves to roots and has sieve-tube elements with companion cells; plasmodesmata extend between cells at sieve plates.
Both tracheids and vessel elements are hollow and nonliving, but vessel elements are larger, lack transverse end walls, and are arranged to form a continuous pipeline for water and minerals. The elongated tracheids, with tapered ends, form a less obvious means of transport, but water can move across the end walls and side walls through pits where the secondary wall does not form. Xylem also contains parenchyma cells that store various substances, and fibers and sclerenchyma cells that lend support.
The conducting cells of phloem are sieve-tube elements each of which has a companion cell. Sieve-tube elements contain cytoplasm but no nuclei. These elements have channels in their end walls that in cross section make them resemble a sieve. Plasmodesmata (sing., plasmodesma), which are strands of cytoplasm, extend from one cell to another through this sieve plate. The smaller companion cells have a nucleus in addition to cytoplasm; the nucleus of the companion cell controls both the companion cell and the sieve-tube element.
Vascular tissue is located in the vascular cylinder in dicot roots, in vascular bundles within stems, and in leaf veins in leaves.

20. Xylem structure Leaves
Xylem transports water and minerals from roots to leaves
Contains two types of conducting cells: tracheids and vessel elements.
Water
This drawing shows the general organization of xylem tissue.
Roots

21. Phloem structure Leaves
Roots
Organic nutrients
Transports organic nutrients from leaves to roots
Has sieve-tube elements with companion cells
Plasmodesmata extend between cells at sieve plates.
This drawing shows the general organization of phloem tissue.

22. Leaves (produce organic nutrients by photosynthesis)
Phloem Xylem
Carries Organic Nutrients Carries Water and Nutrients
Roots (absorb water and minerals from the soil)

23. Organization of Roots
Within a root are zones where cells are in various stages of differentiation.

24. Dicot root tip
In the zone of maturation, mature cells are differentiated and epidermal cells have root hairs.
In the zone of elongation, cells become longer as they specialize.
The root apical meristem is in the zone of cell division; the root cap is a protective covering for the root tip.

25. Dicot root tip
Fig. 9.8
Epidermis – single layer of thin-walled, rectangular cells; root hairs present in zone of maturation
The root tip is divided into three zones and a root cap, best seen in a longitudinal section such as this. The cells in the root cap have to be continually replaced because they are ground off as the root pushes through rough soil particles. In the zone of elongation, the cells become longer as they become specialized. In the zone of maturation, the cells are mature and fully differentiated. This zone is recognizable even in a whole root because root cells are borne by many of the epidermal cells.

26. Movement of materials into vascular cylinder of the root
Fig. 9.8
Endodermis – between cortex and vascular cylinder, single layer of endodermal cells bordered by the Casparian strip
Cortex – thin-walled, loosely-packed parenchyma; starch granules store food
Because of the Casparian strip, water and minerals must pass through the cytoplasm of the endodermal cells in order to enter the vascular cylinder. In this way, endodermal cells regulate the passage of minerals into the vascular cylinder.
regulates entrance of minerals into the vascular cylinder
Layer of impermeable lignin and suberin

27. In Dicot Roots Vascular Tissue is star-shaped; phloem in separate regions between arms of xylem
Fig. 9.8
The pericycle is the first layer of cells within the vascular cylinder.

28. Branching and Taproot of dicots
Fig. 9.9
Pericycle can start the development of branch roots.
In some dicot plants, a primary root, or taproot, grows straight down and is the dominant root; it can be fleshy and stores food.
This cross section of a willow shows the origination of a branch root from the pericycle.

29. Organization of Monocot Roots
Monocot roots have the same growth zones as a dicot root but they DO NOT undergo secondary growth (become woody).
In a monocot root’s centrally located pith, ground tissue is surrounded by a vascular ring.
See Fig. 9.10

30. Monocot root
Fig. 9.11
This cross section enlargement of a monocot root shows the exact placement of various tissues. Note the vascular ring around a central pith.
Monocots have a large number of slender roots, which make up a fibrous root system, and are known as adventitious roots.
Adventitious roots that emerge from the surface to help anchor the plant are called prop roots.
-used for support

31. Fig. 9.11
Some plants are parasitic on other plants. Their stems have rootlike projections called haustoria that grow into the host plant and extract water and nutrients from the host.
Dodder is a parasitic plant consisting mainly of orange-brown twining stems. The green in the photograph is the host plant. Haustoria are rootlike projections of a stem that tap into the host’s vascular system.

32. Other Root Diversity
Mycorrhizae - mutualistic association between roots (better water absorption) and fungi (receive sugars, etc.)
Peas and other legumes have root nodules in which nitrogen-fixing bacteria live.
Nitrogen-fixing bacteria remove nitrogen from the atmosphere and make it available to the plants. Otherwise, plants have to rely on soil nitrogen which is often in limited supply.

33. Organization of Stems Shoot tip
Fig. 9.12
produces new cells that elongate and add length to the stem.
The shoot apical meristem within a terminal bud is surrounded by leaf primordia.

34. Primary tissues are new tissues formed each year from primary meristems right behind apical meristem.
Meristem – Embryonic Tissue (undifferentiated) that develops into specialized tissue.

35. Fate of Primary Meristems
Fig. 9.12
Protoderm gives rise to epidermis.
Ground meristem produces parenchyma in the pith and cortex.
Procambium produces primary xylem and primary phloem; later, vascular cambium occurs between xylem and phoem.
The shoot apical meristem produces the primary meristems: protoderm gives rise to epidermis, ground meristem gives rise to pith and cortex, and procambium gives rise to vascular tissue, including primary xylem, primary phloem, and vascular cambium.

36. Herbaceous (nonwoody) Stems
Mature herbaceous stems exhibit only primary growth (not secondary).
The outermost tissue is the epidermis (not bark), which is covered by a waxy cuticle.
The waxy cuticle of herbaceous stems helps to prevent water loss.
The distinct ring of herbaceous dicot stems separates the cortex from the central pith, which stores water and the products of photosynthesis. The cortex is sometimes green and carries on photosynthesis, and the pith may function as a storage site. Monocot stems have no well-defined cortex or pith.

37. Herbaceous Dicot Stem -vascular bundles are in a distinct ring
Fig. 9.13

38. Monocot stem -vascular bundles are scattered throughout
Fig. 9.14

39. Woody Stems A woody plant has both primary and secondary tissues.
Secondary tissues develop during the second and subsequent years of growth from lateral meristems (vascular cambium and cork cambium).
Secondary growth, (annual growth) increases the girth of a plant.

40. Dicot stems
Fig. 9.15
The drawing in the upper left shows a dicot stem with no secondary growth. The other diagram shows a dicot stem with some secondary growth. Cork has replaced the epidermis, and vascular tissue produces secondary xylem and secondary phloem.
The secondary tissues produced by the vascular cambium, are called secondary xylem and secondary phloem,

41. Secondary growth in a dicot stem
Fig. 9.15
Pith rays are composed of living parenchyma cells that allow materials to move laterally.
Cork cambium replaces epidermis with cork cells impregnated with suberin.
This shows a three-year-old stem in which cork cambium produces new cork. The primary phloem and cortex will eventually disappear, and only the secondary phloem (within thet bark), produced by vascular cambium, will be active that year. The secondary xylem, also produced by vascular cambium, builds up to become annual growth rings.

42. Section of woody stem
Fig. 9.15
The bark of a tree contains cork, cork cambium, and phloem.
A woody stem has three distinct areas: the pith, the wood, and the bark.
Spring wood followed by summer wood makes up one year’s growth or annual ring.
This section of a woody stem shows tissues at a higher magnification.

43. Annual Rings
This tree had a pith date of 256 BC and an outer ring of about AD 1320, making this tree nearly 1,600 years old when it died (it's about 3 feet across)!
(photo © H.D. Grissino-Mayer and R.K. Adams).
It is possible to tell the age of a tree by counting annual rings.

44. Tree trunk
Fig. 9.16
The relationship of bark (cork and phloem), vascular cambium, and wood is retained in a mature stem. The pith has disappeared.
In older trees, the inner annual rings, called heartwood, no longer function in water transport. The cells become plugged with deposits, such as resins, gums, and other substances that inhibit the growth of bacteria and fungi. Heartwood may help support a tree, although some trees live for many years after the heartwood has rotted away.

45. Modified stems
Fig. 9.17
A strawberry plant has aboveground, horizontal stems called stolons. Every other node produces a new shoot system. The underground stem of an iris is a fleshy rhizome.

46. Organization of Leaves
Fig. 9.18
Helps prevent water loss
Photosynthesis
Photosynthesis and Increased area for gas exchange
gas exchange

47. The body of the leaf is composed of mesophyll.
Parenchyma cells of these mesophyll layers house chloroplasts.
The loosely packed arrangement of the cells in the spongy layer increases the amount of surface area for gas exchange.

48. Classification of leaves
Fig. 9.19
The cottonwood tree has a simple leaf. The shagbark hickory has a pinnately compound leaf. The honey locust has a twice pinnately compound leaf. The buckeye has a palmately compound leaf.

49. Leaf diversity
Fig. 9.20
The spines of a cactus plant are leaves modified to protect the fleshy stem from animal consumption and limit the loss of water. The tendrils of a cucumber are leaves modified to attach the plant to a physical support. The leaves of the Venus’s flytrap are modified to serve as a trap for insect prey. When triggered by an insect, the leaf snaps shut. Once shut, the leaf secretes digestive juices, which break down the soft parts of the prey’s body, allowing nutrients such as nitrogen to be absorbed by the plant body.
The leaves of a few plants are specialized for catching insects.
The leaves of a cactus are spines attached to a succulent stem.
Climbing leaves are modified into tendrils.