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Chapter 31

Chapter 31. Plant Structure, Reproduction, and Development. A Gentle Giant The General Sherman giant sequoia is the largest plant on Earth 2,500 years old 84-m tall 1,400-ton trunk A gymnosperm, bearing seeds in cones

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Chapter 31

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  1. Chapter 31 Plant Structure, Reproduction, and Development

  2. A Gentle Giant • The General Sherman giant sequoia is the largest plant on Earth • 2,500 years old • 84-m tall • 1,400-ton trunk • A gymnosperm, bearing seeds in cones • Angiosperms, bearing seeds in flowers, make up more than 90% of the plant kingdom

  3. TALKING ABOUT SCIENCE • 31.1 Plant scientist Natasha Raikhel studies the Arabidopsis plant as a model biological system • Natasha Raikhel is one of America's most prominent plant biologists • Dr. Raikhel uses Arabidopsis (mustard plant) to study • Biological systems • Structure–function relationship in plants

  4. PLANT STRUCTURE AND FUNCTION • 31.2 The two main groups of angiosperms are the monocots and the dicots • Cotyledons are seed (embryonic) leaves • Monocots • One cotyledon • Main veins usually parallel • Vascular bundles in complex arrangement • Floral parts usually in multiples of three • Fibrous root system

  5. Dicots • Two cotyledons • Main veins usually branched • Vascular bundles arranged in ring • Floral parts usually in multiples of four or five • Taproot usually present

  6. LE 31-02 Seed leaves Leaf veins Stems Flowers Roots MONOCOTS One cotyledon Main veins usually parallel Vascular bundles in complex arrangement Floral parts usually in multiples of three Fibrous root system DICOTS Two cotyledons Floral parts usually in multiples of four or five Main veins usually branched Vascular bundles arranged in ring Taproot usually present

  7. 31.3 A typical plant body consists of roots and shoots • A plant is adapted to draw resources from two different environments • Root system • Anchors plant in the soil • Absorbs and transports minerals and water • Root hairs increase absorptive surface • Stores food

  8. Shoot system • Obtains CO2 and light from air • Stem, with nodes and internodes, supports leaves and flowers • Leaves are main photosynthetic organs • Flowers are reproductive organs • Terminal and axillary buds • Apical dominance is an evolutionary adaptation that increases the plant's exposure to light

  9. LE 31-03 Terminal bud Blade Leaf Flower Petiole Axillary bud Stem Shoot system Node Root hair Internode Root hairs Taproot Root system Epidermal cell

  10. 31.4 Many plants have modified roots, stems, and leaves • Roots, stems, and leaves are adapted for a variety of functions • Modified roots store sugar • Modified stems • Stolons enable a plant to reproduce asexually • Rhizomes store food and can form new plants • Tubers are structures specialized for storage

  11. LE 31-04b Strawberry plant Potato plant Stolon (runner) Taproot Ginger plant Rhizome Tuber Rhizome Root

  12. Modified leaves • Store food or water • Function in protection of plant • Aid in climbing (tendrils)

  13. 31.5 Plant cells and tissues are diverse in structure and function • Most plant cells have three unique structures • Chloroplasts, the sites of photosynthesis • A central vacuole containing fluid • A cell wall that surrounds the plasma membrane

  14. LE 31-05a Chloroplast Central vacuole Nucleus Cell walls Primary cell wall Endoplasmic reticulum Secondary cell wall Middle lamella Mitochondrion Golgi apparatus Cell walls of adjoining cells Ribosomes Plasma membrane Microtubules Plasmodesmata Pit Plasma membrane

  15. Plants have five major types of cells • Parenchyma: perform most of the plant's metabolic functions • Collenchyma: provide support • Sclerenchyma: form a rigid skeleton that supports the plant; the main component of wood • Fibers: long cells arranged in bundles • Sclereids: shorter, have very hard secondary walls

  16. LE 31-05b Primary cell wall (thin) LM 270 Pit Starch-storing vesicles

  17. LE 31-05c Primary cell wall (thick) LM 270

  18. LE 31-05d Sclereid cells Secondary cell wall Pits Secondary cell wall Fiber cells LM 266 LM 200 Primary cell wall Pits Primary cell wall Fiber Sclereid

  19. Water-conducting cells in angiosperms • Tracheids and vessel elements • Hollow tubes of dead cell walls • Food-conducting cells • Sieve-tube members separated by sieve plates • Companion cells • Vascular tissue • Xylem: conveys water and minerals • Phloem: transports sugars

  20. LE 31-05e Pits Vessel element Tracheids Pits Openings in end wall  Colorized SEM 150

  21. LE 31-05f Sieve plate Companion cell Primary cell wall LM 45 Cytoplasm

  22. 31.6 Three tissue systems make up the plant body • A tissue system consists of one or more tissues organized into a functional unit • Dermal tissue system forms outer protective covering of the plant • Epidermis • Cuticle

  23. Vascular tissue system • Contains xylem and phloem • Provides long-distance transport and support • Ground tissue system • Most of the bulk of young plants • Pith: internal to vascular tissue • Cortex: external to vascular tissue

  24. Arrangement of tissue systems in root • Vascular cylinder is in center • Xylem radiates out • Phloem fills in spaces • Ground tissue system consists entirely of cortex • Endodermis is one-cell-thick innermost layer

  25. Arrangement of tissue systems in stem • Vascular tissue in vascular bundles • Dicot: arranged in a ring • Monocot: scattered throughout ground tissue • Ground tissue • Dicot: has both cortex and pith regions • Monocot: Not divided into regions

  26. Arrangement of tissue systems in leaf • Epidermis interrupted by stomata flanked by guard cells • Mesophyll ground tissue sandwiched between lower and upper epidermis • Vascular system made up of network of veins

  27. LE 31-06 Dicot leaf Cuticle Upper epidermis Xylem Vein Phloem Mesophyll Guard cells Lower epidermis Stoma Sheath Dicot stem Monocot stem Vascular bundle Vascular bundle Cortex Pith Epidermis Epidermis Xylem Vascular cylinder Phloem Key Epidermis Dermal tissue system Ground tissue system Vascular tissue system Cortex Endodermis Dicot root

  28. PLANT GROWTH • 31.7 Primary growth lengthens roots and shoots • Plants undergo indeterminate growth but are not immortal • Flowering plants are categorized based on length of life cycle • Annuals: complete life cycle in a single year or less • Biennials: complete life cycle in two years • Perennials: live and reproduce for many years

  29. Primary growth enables a plant to grow in length • Apical meristems are unspecialized cells that continue to give rise to new cells • Located in the tips of roots and the terminal and axillary buds of shoots • Covered by a protective root cap that is sloughed off during growth

  30. LE 31-07a Terminal bud Axillary buds Arrows = direction of growth Root tips

  31. Primary growth occurs behind the root tip in three zones • Zone of cell division • Zone of elongation • Zone of maturation Video: Root Growth in a Radish Seed (time lapse)

  32. LE 31-07b Vascular cylinder Cortex Root hair Epidermis Zone of maturation Zone of elongation Cellulose fibers Zone of cell division Apical meristem region Key Root cap Dermal tissue system Ground tissue system Vascular tissue system

  33. LE 31-07c Leaves Apical meristem Axillary bud meristems LM 103

  34. 31.8 Secondary growth increases the girth of woody plants • Secondary growth is produced by lateral meristems, two cylinders of dividing cells • Vascular cambium • Lies between primary xylem and primary phloem • Thickens a stem by adding secondary xylem and phloem on both sides • Cork cambium • Makes cork, a new outer layer of epidermis

  35. Bark comprises everything external to the vascular cambium • Layers sloughed off as secondary xylem expands outward • Wood is made of secondary xylem • Heartwood: older layers of secondary growth in center of tree that no longer function in transport • Sapwood: younger secondary xylem that conducts xylem sap • Wood rays: parenchyma cells that transport water to outer living tissue

  36. LE 31-08a Year 2 Late Summer Year 1 Late Summer Year 1 Early Spring Key Dermal tissue system Ground tissue system Vascular tissue system Shed epidermis Growth Growth Growth Growth Primary xylem Epidermis Cork Secondary xylem (wood) Vascular cambium Secondary xylem (2 years’ growth) Cortex Cork cambium Bark Primary phloem Secondary phloem

  37. LE 31-08b Sapwood Rings Wood rays Heartwood Sapwood Vascular cambium Secondary phloem Cork cambium Cork Bark Heartwood

  38. REPRODUCTION OF FLOWERING PLANTS • 31.9 Overview: The sexual life cycle of a flowering plant • The angiosperm flower consists of four types of modified leaves • Sepals enclose and protect bud • Petals advertise flower to pollinators • Stamen: male reproductive organ • Pollen grains develop in anther at tip of filament

  39. Carpel: female reproductive organ • Stigma, at tip of style, receives pollen grains • Ovary at base of carpel houses ovules • Contain developing egg and supporting structures Video: Flower Blooming (time lapse) Video: Time Lapse of Flowering Plant Life Cycle

  40. LE 31-09a Stigma Carpel Stamen Style Anther Ovary Filament Petal Ovule Sepal

  41. Life cycle of an angiosperm • Fertilization occurs in ovule • Ovule develops into seed containing embryo • Ovary develops into fruit • Seed germinates • Embryo develops into seedling • Seedling grows into mature plant

  42. LE 31-09b Ovary, containing ovule Embryo Fruit (mature ovary), containing seed Seed Mature plant with flowers, where fertilization occurs Seedling Germinating seed

  43. 31.10 The development of pollen and ovules culminates in fertilization • The plant life cycle includes alternation of haploid and diploid generations • Diploid sporophyte produces haploid spores by meiosis • Spores divide by mitosis, becoming microscopic, multicellular, haploid gametophytes

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