SC.912.L.14.7Plant Structures and Functions

1. SC.912.L.14.7Plant Structures and Functions

2. Plant Structures and Functions • 1. Monocots vs. Dicots • Root structure and vasculature • Stem vasculature • Leaf structure and vasculature • 2. Plant tissues • Dermal (epidermis) • Vascular • Ground • Meristematic • 3. Plant organs • Roots • Stems • Leaves • Flowers and Cones • 4. Plant Growth • Meristems – apical, axillary, lateral • Vascular cambium vs. cork cambium

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

4. Plant “bodies” Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells Shoot system Leaf Stem Three Basic Plant Organs: Roots, Stems, and Leaves Root system

5. Dermal tissue Ground tissue Vascular tissue Plant Tissues • Each plant organ has dermal, vascular, and ground tissues • Each of these three categories forms a tissue system

6. Plant Tissues • 1) Dermal Tissue System • Outer covering • Protection • 2) Vascular Tissue System • “Vessels” throughout plant • Transport materials • 3) Ground Tissue System • “Body” of plant • Photosynthesis; storage; support

7. Plant Tissues - Dermis Dermal Tissue System (Outer Covering of Plant): • 1) Epidermal Tissue (epidermis): • Forms outermost layer • Cuticle: Waxy covering • Reduces evaporation • Inhibits microorganism invasion • Root Hairs: extended root surface • Increase absorption • 2) Peridermal Tissue (periderm): • Only in woody plants (“bark = dead cells”) • Protection; support

8. 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

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

10. Plant Tissues - Vascular 1) Xylem (dead at maturity): • Tracheids: Narrow, tube-like cells • Vessel Elements: Wide, tube-like cells

11. Plant Tissues - Vascular Vascular Transport System 1) Xylem (dead at maturity): - Moves water & minerals from roots to shoots

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

13. Plant Tissues - Vascular Vascular Transport System 2) Phloem (living at maturity) - Moves water, sugar, amino acids & hormones

14. Vasculature - Comparisons Monocots and dicots differ in the arrangement of vessels in the roots and stems • Dicots • Monocots Stem Root

15. Plant Tissues – Ground Tissue • Some major types of plant cells: • Parenchyma • Collenchyma • Sclerenchyma • 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

16. Plant Tissues - Ground Ground Tissue System (“Body” of Plant): 1) Parenchyma (most abundant): Thin-walled cells; living • plant metabolism: Photosynthesis; hormone secretion; sugar storage Parenchyma cells in Elodea leaf,(w/chloroplasts)

17. Plant Tissues - Ground Ground Tissue System (“Body” of Plant): 2) Collenchyma: Thick-walled (uneven); living • Offers support (flexible & strong) Collenchyma cells sunflower

18. Sclereid cells in pear (LM) Cell wall Fiber cells in ash tree Plant Tissues - Ground Ground Tissue System (“Body” of Plant): 3) Sclerenchyma: Thick, hard-walled; Dead • Offer support (e.g. hemp fibers; nut shells)

19. 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

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

21. 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

22. Roots – Structure and Development In maturation zone, Casparian strip forms – waterproof barrier material surrounding vasculature

23. Roots – Structure and Development Epidermis Cortex Endodermis Location of Casparian strip Monocot Primary phloem Pericycle Primary xylem Pith 1250 µm 385 µm Endodermis Location of Casparian strip Endodermis Primary xylem Cortex Primary phloem Eudicot Epidermis Pericycle 48 µm 8 µm

24. Prop roots “Strangling” aerial roots Storage roots Buttress roots Pneumatophores Roots – Many Plants Have Modified Roots Water storage

25. Apical bud Node Internode Apical bud Shoot system Vegetative shoot Axillary bud Stem Stems - Overview Stem: an organ made of • An alternating system of nodes, points at which leaves attach • Internodes, stem length between nodes • Axillary bud - structure that can form a lateral shoot, or branch • Apical/terminal bud - located near the shoot tip, lengthens a shoot • Apical dominance maintains dormancy in most nonapical buds

26. Stems – Structure and Development • Stems have all three types of plant tissue • Grow by division at meristems • Develop into leaves, other shoots, and even flowers • Leaves may be arranged in one of three ways

27. Stems - Comparisons Eudicot Monocot

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

29. Shoot system Blade Leaf Petiole Leaves - Overview The leaf is the main photosynthetic organ of most vascular plants Leaves generally have a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem

30. Leaves – Structure and Development • Leaves are several layers thick – each with different cell types

31. Leaves – Structure and Development • Most dicots have 2 types of mesophyll • Palisade mesophyll • high photosynthesis • Spongy mesophyll • air spaces for gas & water exchange • Monocot leaves have 1 type of mesophyll

32. Leaves - Comparisons Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves • Monocots have parallel leaf veins and longer, slender blades • Most dicots have branch-like veins and palmate leaf shape

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

34. 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

35. length girth Plant Growth 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

36. Plant Growth Leaf primordia Shoot apical meristem Young leaf Developing vascular strand Axillary bud meristems

37. Primary growth in stems Epidermis Cortex Shoot tip (shoot apical meristem and young leaves) Primary phloem Primary xylem Pith Lateral meristems: Vascular cambium Secondary growth in stems Cork cambium Periderm Axillary bud meristem Cork cambium Cortex Primary phloem Pith Primary xylem Secondary phloem Root apical meristems Secondary xylem Vascular cambium Plant Growth Two lateral meristems: vascular cambium and cork cambium

38. Plant Growth Stem – Secondary Growth: primary phloem • thicker, stronger stems • Vascular Cambium: between primary xylem and phloem vascular cambium primary xylem epidermis • Produces inside stem: pith • A) Secondary xylem • moves H2O, inward • B) Secondary phloem • moves sugars, outward cortex primary xylem dividing vascular cambium primary phloem

39. Secondary growth secondary phloem primary phloem Growth Vascular cambium Vascular cambium primary xylem X X C P P secondary xylem Secondary phloem Secondary xylem X C P X vascular cambium C X P C pith C cortex C C X C primary xylem C C new secondary xylem After one year of growth After two years of growth C C C dividing vascular cambium new secondary phloem primary phloem Plant Growth Vascular Cambium:

40. Growth ring Vascular ray Heartwood Dead at maturity Protection Secondary xylem Sapwood Vascular cambium Secondary phloem Bark Layers of periderm Plant Growth Stem – Secondary Growth: • Cork Cambium: • Located under outer surface; produces periderm

41. Plant Growth Stem – Secondary Growth: heartwood (xylem) sapwood (xylem) vascular cambium phloem annual ring • Sapwood = Young xylem, water • Heartwood = Old xylem, support • Seasonal Growth = annual rings • Secondary phloem = grows outward older phloem crushed late xylem early xylem

42. Plant Growth RESULTS 2 1.5 Ring-width indexes 1 0.5 0 1600 1700 1800 1900 2000 Year Using dendrochronology to study climate

43. Plant Growth Living tree or dead tree?

44. Plant Growth - Roots Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem 100 µm Phloem 100 µm (a) Root with xylem and phloem in the center (typical of eudicots) (b) Root with parenchyma in the center (typical of monocots) Key to labels Endodermis Pericycle Dermal Ground Vascular Xylem Phloem

45. Plant Growth - Stems Phloem Xylem Ground tissue Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Epidermis Key to labels Vascular bundles Cortex Epidermis Dermal Vascular bundle Ground Vascular 1 mm 1 mm (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots) (b) Cross section of stem with scattered vascular bundles (typical of monocots) • In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring

46. Plant Growth - Leaves Guard cells Key to labels Stomatal pore 50 µm Dermal Epidermal cell Ground Cuticle Sclerenchyma fibers Vascular Stoma (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Palisade mesophyll Spongy mesophyll Bundle- sheath cell Lower epidermis 100 µm Cuticle Xylem Vein Phloem Vein Air spaces Guard cells Guard cells (a) Cutaway drawing of leaf tissues (c) Cross section of a lilac (Syringa)) leaf (LM) • Leaf epidermis contains stomata - allow CO2 exchange • Stomata flanked by two guard cells,control open vs. closed • The ground tissue in a leaf, called mesophyll, fills the middle

47. Plant Structures and Functions Summary • 1. Monocots vs. Dicots • Root structure and vasculature • Stem vasculature • Leaf structure and vasculature • 2. Plant tissues • Dermal (epidermis) • Vascular • Ground • 3. Plant organs • Roots • Stems • Leaves • 4. Plant Growth • Meristems – apical, axillary, lateral • Vascular cambium vs. cork cambium