Plant Structure, Growth, & Development

1. Plant Structure, Growth, & Development Campbell and Reece Chapter 35

2. Organization of Plants • Plants like most multicellular organisms have organs made of tissues that are made of different cell types

3. 3 Basic Plant Organs • Stems • Roots • Leaves

4. Roots • Organ that • anchors a vascular plant in the soil • absorbs water & minerals • stores carbohydrates

5. Taproot System • In most eudicots & gymnosperms • Taproot develops from embryonic root • Forms lateral roots (branch roots) • Penetrate deep • Eudicot: most flowering plants that have 2 embryonic seed leaves • Gymnosperm: vascular plant that bears naked seeds

6. Roots in Monocots • Grasses: no tap root • Roots called adventitious: grows in unusual locations • Example: roots arising from stems or leaves

7. Adventitious Root Systems • Each small root forms its own lateral roots  fibrous root system

8. Root Hairs • Emerge near tips of roots • Increase surface area for absorption of water and mineral ions (do not help anchor plant) • are thin, tubular extensions of a root epidermal cell

9. Root Adaptations • Prop Roots: support tall, top-heavy trees • Pneumatophores: air roots, portion above water line allows them to get O2

10. Root Adaptations • Buttress Roots: tallest trees in rain forest have shallow roots; buttress roots give support to trunks • “Strangling” Aerial Roots: seeds of these trees (strangler fig) germinate in branches of host tree

11. Stems • Plant organs that • raise or separate leaves  allowing them to receive more sunlight • Raise reproductive structures  facilitating dispersal of seeds or pollen

12. Parts of a Stem • Each stem has alternating system of: • Nodes • Pts @ which leaves are attached • Internodes • Stem segments between nodes • Axillary Bud • Upper angle (axil) formed by each leaf & stem • Structure that can form a lateral shoot (branch)

13. Parts of a Stem 4.Apical Bud • Part of shoot tip • The terminal bud (where most of growth occurs) 5. Apical Dominance • Inhibits growth @ axillary buds • If eaten by herbivore or if light more intense @ side of a shoot axillary buds break apical dominance & grow

14. Why Pruning Makes a Plant Bushier

15. Parts of a Stem

16. Adaptations of Stems • Rhizomes: horizontal shoots that grow just below surface ;vertical shoots emerge from axillary buds • Ex: Irises, Hops

17. Stem Adaptations 2.Bulbs: are vertical, underground shoots made mostly of enlarged bases of modified leaves that store food • Ex: onion, tulips

18. Adaptations of Stems 3. Stolons: horizontal shoots that grow along surface; aka “runners” • Enable plant to reproduce asexually: plantlets form @ nodes • Ex: strawberries, some grasses

19. Adaptations of Stems 4. Tubers: enlarged ends of rhizomes or stolons specialized for storing food. “Eye” of potato is cluster of axillary buds that mark the nodes Ex: potato, dahlias

20. Leaves • In most plants leaf is main photosynthetic organ • General Structure: • Blade • Petiole • not on grasses or most monocots • Veins • Patterns differ monocots & eudicots

21. Structure of a Leaf

22. Types of Leaves

23. Leaf Adaptations • Tendrils: modified leaf used to support plant • Ex: pea plants • Some plants have tendrils that are modified stems (grapevines)

24. Leaf Adaptations 2. Spines: leaves adapted for protection In cacti, stems are main photosynthetic organ

25. Leaf Adaptations 3. Storage Leaves: most succulents have leaves adapted to store water

26. Leaf Adaptations 4. Reproductive Leaves: leaves of some succulents produce adventitious plantlets which fall off & take root in soil Ex: some succulents Hens and Chicks

27. Leaf Adaptations 5. Bracts: modified leaves surrounding the real flower; function: attract pollinators The yellow portion of poinsettia is the flower; the red leaves are bracts

28. Tissue Systems • Are functional units connecting all of the plants organs

29. Dermal Tissue System • Plant’s outer protective covering: • Epidermis: nonwoody plants: tightly packed cells • Cuticle: waxy covering on epidermal surface prevents water loss • Periderm: in woody plants: replaces in older regions of stems & roots

30. Vascular Tissue System Carries out long-distance transport of materials between the root & shoot systems • Xylem • H2O & dissolved materials roots  shoots • Phloem • Sugars  roots & sites of growth

31. Ground Tissue System • Tissue that isn’t dermal or vascular tissue • Pith: Internal to vascular tissue • Cortex: external to vascular tissue

32. Plant Cells • Cell differentiation involving changes in: • Cell walls • Cytoplasm • Organelles

33. Parenchymal Cells • Mature cells have thin, slightly flexible cell walls (only 1)& large central vacuole • Functions: • Perform most of metabolic functions of plant • Chloroplasts • Plastids: store starch, found in roots • Make up most of fleshy part of fruits • Most able to divide & differentiate into other cell types

35. Collenchyma Cells • Come grouped in strands just below epidermis • Support young parts of plant shoot w/out interfering with growth • Elongated cells with thicker cell walls (compared to parenchymal cells) which can be irregularly thickened • Remain living cells thru out plant life

37. Sclerenchymal Cells • Supportive role but more rigid than collenchymal cells in regions of plant that have stopped growing • 2º cell walls thick, contain lignin (>1/4 dry mass of wood)Lignin in all vascular plants, not in bryophytes • Many dead at plant maturity: rigid cell walls support plant

38. Sclerenchymal Cells • 2 types: (both for support & strength) • Sclereids • Boxy, irregularly shaped cells • Thick lignified 2º cell walls • Hardness in nutshells/grittiness in pear • Fibers • Grouped in strands • Long, slender, tapered • Hemp fibers for rope/flax fibers for linen

40. Water-Conducting Cells of Xylem • 2 types: both elongated, tubular cells/dead at plant maturity: form tubular conduit for water flow; have pits thru which water can move laterally • Tracheids • In nearly all vascular plants • Vessel Elements • In some vascular/most angiosperms/few gymnosperms

42. Sugar-Conducting Cells of the Phloem • 4 types all alive @ plant maturity • Sieve Cells: in seedless vascular plants & gymnosperms • Sieve Tubes: chains of cells/ enucleated, no ribosomes, vacuole, or cytoskeleton  sugars can diffuse thru cell more easily • Sieve Plates: pores for flow of sap fluid cell-to-cell • Companion Cells: nonconducting cells connected to sieve tube cells by plasmodesmata/their ribosomes & nucleus serve both cells

45. Growth in Plants

46. Stem Growth

47. Root Growth

48. Cross-Section of a Leaf

49. Anatomy of a Tree Trunk • bark includes all tissues external to the vascular cambian (2º xylem, wood, and phloem) • Sapwood = “living wood” has lighter color than heart wood (center) which is made of dead cells