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Plant Organs: Roots Chapter 6. KEY TERMS TAPROOT SYSTEM TAPROOT SYSTEM A root system consisting of one prominent main root with smaller lateral roots.

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Presentation on theme: "Plant Organs: Roots Chapter 6. KEY TERMS TAPROOT SYSTEM TAPROOT SYSTEM A root system consisting of one prominent main root with smaller lateral roots."— Presentation transcript:

1 Plant Organs: Roots Chapter 6

2 KEY TERMS TAPROOT SYSTEM TAPROOT SYSTEM A root system consisting of one prominent main root with smaller lateral roots branching from it A root system consisting of one prominent main root with smaller lateral roots branching from it FIBROUS ROOT SYSTEM FIBROUS ROOT SYSTEM A root system consisting of several adventitious roots of approximately equal size that arise from the base of the stem A root system consisting of several adventitious roots of approximately equal size that arise from the base of the stem

3 Root Systems

4 LEARNING OBJECTIVE 1 Describe the functions of roots Describe the functions of roots Describe two features of roots that shoots lack Describe two features of roots that shoots lack

5 Functions of Roots Anchorage Anchorage Absorption Absorption Conduction Conduction Storage Storage

6 Storage Roots

7 KEY TERMS ROOT CAP ROOT CAP A covering of cells over the root tip that protects delicate meristematic tissue directly behind it A covering of cells over the root tip that protects delicate meristematic tissue directly behind it ROOT HAIR ROOT HAIR An extension of an epidermal cell of a root that increases absorptive capacity of the root An extension of an epidermal cell of a root that increases absorptive capacity of the root

8 Root Cap Each root tip has a root cap Each root tip has a root cap A protective thimblelike layer A protective thimblelike layer Many cells thick Many cells thick Covers delicate root apical meristem Covers delicate root apical meristem May orient root so it grows downward May orient root so it grows downward

9 Root Hairs Short-lived, unicellular extensions of epidermal cells near the growing root tip Short-lived, unicellular extensions of epidermal cells near the growing root tip Increase surface area of root in contact with moist soil, increasing root’s absorptive capacity Increase surface area of root in contact with moist soil, increasing root’s absorptive capacity

10 Structures Unique to Roots

11 Root apical meristem (area of cell division) Root cap (a) The root cap of an onion (Allium cepa) root. The root cap protects the root’s apical meristem. Fig. 6-3a, p. 114

12 Root hairs Soil air Soil water Soil particles Epidermis (b) Root hairs on a radish (Raphanus sativus) seedling. Each delicate hair is a unicellular extension of the root epidermis. Root hairs increase the surface area in contact with the soil. Fig. 6-3b, p. 114

13 LEARNING OBJECTIVE 2 Contrast the structure of a primary eudicot root and a monocot root Contrast the structure of a primary eudicot root and a monocot root Describe the functions of each tissue Describe the functions of each tissue

14 Primary Eudicot Roots 1 Outer protective covering Outer protective covering Epidermis Epidermis Ground tissues Ground tissues Cortex Cortex Pith (in certain roots) Pith (in certain roots) Vascular tissues Vascular tissues Xylem Xylem Phloem Phloem

15 Primary Eudicot Roots 2 Epidermis Epidermis Protects the root Protects the root Root hairs help absorb water and dissolved minerals Root hairs help absorb water and dissolved minerals Cortex Cortex Consists of parenchyma cells Consists of parenchyma cells Usually stores starch Usually stores starch

16 KEY TERMS ENDODERMIS ENDODERMIS Innermost layer of the cortex of the root that prevents water and dissolved materials from entering the xylem by passing between cells Innermost layer of the cortex of the root that prevents water and dissolved materials from entering the xylem by passing between cells

17 KEY TERMS CASPARIAN STRIP CASPARIAN STRIP A band of waterproof material around the radial and transverse cells of the endodermis A band of waterproof material around the radial and transverse cells of the endodermis Ensures that water and minerals enter the xylem only by passing through the endodermal cells Ensures that water and minerals enter the xylem only by passing through the endodermal cells

18 Endodermis and Mineral Uptake

19 Endodermis Epidermis Root cross section Casparian strip Movement of water through the endodermis to the center of the root Endodermis Casparian strip Cortex Fig. 6-5, p. 118

20 KEY TERMS PERICYCLE PERICYCLE A layer of cells just inside the endodermis of the root A layer of cells just inside the endodermis of the root Gives rise to lateral roots Gives rise to lateral roots

21 Lateral Root

22 Fig. 6-7, p. 120

23 Willow Pericycle Cortex Lateral root Ruptured epidermis Fig. 6-7, p. 120

24 Primary Eudicot Roots 3 Xylem Xylem conducts water and dissolved minerals conducts water and dissolved minerals Phloem Phloem conducts dissolved sugar conducts dissolved sugar

25 Herbaceous Eudicot Root

26 Buttercup Cortex Stele (a) Cross section of a buttercup (Ranunculus) root. Note that the bulk of the root is the cortex. Epidermis Fig. 6-4a, p. 116

27 Cortex cells filled with amyloplasts Endodermis cell Pericycle cell Xylem vessel elements Intercellular space (b) A close-up of the stele of the buttercup root. Note the solid core of vascular tissues. Phloem cell Fig. 6-4b, p. 116

28 Comparing Monocot and Eudicot Monocot roots often have a pith in the center of the root Monocot roots often have a pith in the center of the root In herbaceous eudicot roots, xylem and phloem form a solid mass in center of root In herbaceous eudicot roots, xylem and phloem form a solid mass in center of root Monocot roots lack a vascular cambium Monocot roots lack a vascular cambium Do not have secondary growth Do not have secondary growth

29 Monocot Root

30

31 Stele Cortex Epidermis Greenbrier Fig. 6-8a, p. 121

32 Pith Vascular tissues Xylem Phloem Pericycle Endodermis Fig. 6-8b, p. 121

33 LEARNING OBJECTIVE 3 Trace the pathway of water from the soil through the various root tissues Trace the pathway of water from the soil through the various root tissues

34 Water Movement 1 In a primary eudicot root, water moves from soil into center of root: In a primary eudicot root, water moves from soil into center of root: Root hair → epidermis → cortex (symplast or apoplast pathway) → endodermis → pericycle → xylem of root Root hair → epidermis → cortex (symplast or apoplast pathway) → endodermis → pericycle → xylem of root Water is transported upward through root xylem into stem xylem and rest of plant Water is transported upward through root xylem into stem xylem and rest of plant

35 KEY TERMS SYMPLAST SYMPLAST A continuum consisting of the cytoplasm of many plant cells, connected from one cell to the next by plasmodesmata A continuum consisting of the cytoplasm of many plant cells, connected from one cell to the next by plasmodesmata APOPLAST APOPLAST A continuum consisting of the interconnected, porous plant cell walls, along which water moves freely A continuum consisting of the interconnected, porous plant cell walls, along which water moves freely

36 Symplast and Apoplast

37 Xylem vessels Phloem cells Pericycle Plasma membrane Plasmodesma Cell wall Apoplast: interconnected cell-wall spaces Root hair Water and dissolved nutrient minerals Symplast: interconnected cytoplasm of living cells Epidermis Cortex Casparian strip Endodermis Movement upward Fig. 6-6, p. 119

38 LEARNING OBJECTIVE 4 Describe several roots that are modified to perform unusual functions Describe several roots that are modified to perform unusual functions

39 KEY TERMS PROP ROOT PROP ROOT An adventitious root that arises from the stem and provides additional support for the plant An adventitious root that arises from the stem and provides additional support for the plant CONTRACTILE ROOT CONTRACTILE ROOT A specialized root, often found on bulbs or corms, that contracts and pulls the plant to a desirable depth in the soil A specialized root, often found on bulbs or corms, that contracts and pulls the plant to a desirable depth in the soil

40 Prop Roots

41 Contractile Roots

42 (a) Plants that produce corms or bulbs often have contractile roots that lose much of their length as root cells shorten and broaden. Contractile roots Corm Fig. 6-13a, p. 124

43 Contractile roots Fig. 6-13b, p. 124

44 KEY TERMS PNEUMATOPHORE PNEUMATOPHORE A specialized aerial root produced by certain trees living in swampy habitats A specialized aerial root produced by certain trees living in swampy habitats May facilitate gas exchange between the atmosphere and submerged roots May facilitate gas exchange between the atmosphere and submerged roots

45 Pneumatophores

46 Other Modified Roots 1 Buttress roots Buttress roots Swollen bases or braces that hold trees upright Swollen bases or braces that hold trees upright Aid in extensive distribution of shallow roots Aid in extensive distribution of shallow roots Found in some tropical rainforest trees Found in some tropical rainforest trees

47 Buttress Roots

48 Other Modified Roots 2 Suckers Suckers Aboveground stems that develop from adventitious buds on the roots Aboveground stems that develop from adventitious buds on the roots Asexual reproduction method of some roots Asexual reproduction method of some roots Certain epiphytes have roots that are modified to photosynthesize Certain epiphytes have roots that are modified to photosynthesize

49 Parasitic Epiphytes

50 (b) Micrograph of a parasitized juniper (Juniperus) branch, showing a mistletoe root penetrating the wood (secondary xylem) of the juniper. Juniper wood Mistletoe root Juniper bark Fig. 6-12b, p. 123

51 LEARNING OBJECTIVE 5 Discuss the significance of roots to humans Discuss the significance of roots to humans

52 Important Foods Roots which store the products of photosynthesis are important sources of food for human consumption Roots which store the products of photosynthesis are important sources of food for human consumption Some roots are used as flavorings Some roots are used as flavorings Example: root beer flavoring (dried greenbrier roots) Example: root beer flavoring (dried greenbrier roots)

53 Root Crops Predominantly taproots Predominantly taproots carrots, beets, sugar beets, parsnips, turnips, rutabagas, radishes carrots, beets, sugar beets, parsnips, turnips, rutabagas, radishes Some fibrous roots Some fibrous roots sweet potatoes, cassava sweet potatoes, cassava

54 KEY TERMS MYCORRHIZA MYCORRHIZA A mutually beneficial association between a fungus and a root that helps the plant absorb essential minerals from the soil A mutually beneficial association between a fungus and a root that helps the plant absorb essential minerals from the soil NODULE NODULE A small swelling on the root of a leguminous plant in which beneficial nitrogen-fixing bacteria (Rhizobium) live A small swelling on the root of a leguminous plant in which beneficial nitrogen-fixing bacteria (Rhizobium) live

55 Mycorrhizae

56 Fungal hypha between plant cells Sheath of fungal hyphae encircles root (a) Cross section of root showing ectomycorrhizae, fungal associations that form a sheath around the root. The fungal hyphae penetrate the root between cortical cells but do not enter the cells. Fig. 6-14a, p. 124

57 Fungal hyphae within plant cortical cells (b) Cells of a root cortex showing endomycorrhizae, fungal associations in which the fungal hyphae penetrate root cells of the cortex to aid in delivering and receiving nutrients. Endomycorrhizae colonize roots of most vascular plant species. Fig. 6-14b, p. 124

58 Animation: Root Systems CLICK TO PLAY

59 Animation: Water Absorption CLICK TO PLAY

60 Animation: Root Functioning CLICK TO PLAY

61 Root Animation: Root Cross- section CLICK TO PLAY


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