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Chapter 35

Chapter 35. Plant Structure, Growth, and Development. The Three Basic Plant Organs: Roots, Stems, and Leaves. Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below-ground and above-ground. Reproductive shoot (flower). Terminal bud. Node.

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Chapter 35

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  1. Chapter 35 Plant Structure, Growth, and Development

  2. The Three Basic Plant Organs: Roots, Stems, and Leaves • Basic morphology of vascular plants reflects their evolution as organisms that draw nutrients from below-ground and above-ground

  3. Reproductive shoot (flower) Terminal bud Node • Three basic organs evolved: roots, stems, and leaves • They are organized into a root system and a shoot system Internode Terminal bud Shoot system Vegetable shoot Blade Leaf Petiole Axillary bud Stem Taproot Lateral roots Root system

  4. Roots • Functions of roots: • Anchoring the plant • Absorbing minerals and water • Often storing organic nutrients

  5. LE 35-4a Prop roots.

  6. LE 35-4b Storage roots.

  7. LE 35-4c “Strangling” aerial roots.

  8. LE 35-4d Buttress roots.

  9. LE 35-4e Pneumatophores.

  10. Stems • A stem is an organ consisting of • An alternating system of nodes, the points at which leaves are attached • Internodes, the stem segments between nodes

  11. An axillary bud is a structure that has the potential to form a lateral shoot, or branch • A terminal bud is located near the shoot tip and causes elongation of a young shoot

  12. LE 35-5a Stolons.

  13. LE 35-5b Storage leaves Stem Roots Bulbs.

  14. LE 35-5c Tubers.

  15. LE 35-5d Rhizomes. Node Rhizome Root

  16. Leaves • The leaf is the main photosynthetic organ of most vascular plants • Leaves generally consist of • A flattened blade and a stalk • The petiole, which joins the leaf to a node of the stem

  17. Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves • Most monocots have parallel veins • Most eudicots have branching veins

  18. LE 35-6a Simple leaf Petiole Axillary bud

  19. LE 35-6b Leaflet Compound leaf Petiole Axillary bud

  20. LE 35-6c Doubly compound leaf Leaflet Petiole Axillary bud

  21. Some plant species have evolved modified leaves that serve various functions

  22. LE 35-7a Tendrils.

  23. LE 35-7b Spines.

  24. LE 35-7c Storage leaves.

  25. LE 35-7d Bracts.

  26. LE 35-7e Reproductive leaves.

  27. The Three Tissue Systems: Dermal, Vascular, and Ground • Each plant organ has dermal, vascular, and ground tissues Dermal tissue Ground tissue Vascular tissue

  28. In nonwoody plants, the dermal tissue system consists of the epidermis • In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots

  29. The vascular tissue system carries out long-distance transport of materials between roots and shoots • The two vascular tissues are xylem and phloem • Xylem conveys water and dissolved minerals upward from roots into the shoots • Phloem transports organic nutrients from where they are made to where they are needed

  30. The vascular tissue of a stem or root is collectively called the stele • In angiosperms • Roots: • Stems and leaves divided into vascular bundles:

  31. Ground tissue includes cells specialized for storage, photosynthesis, and support

  32. Some major types of plant cells: • Parenchyma • Collenchyma • Sclerenchyma • Water-conducting cells of the xylem • Sugar-conducting cells of the phloem

  33. LE 35-9 WATER-CONDUCTING CELLS OF THE XYLEM PARENCHYMA CELLS 100 µm Tracheids Vessel Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm Pits COLLENCHYMA CELLS Cortical parenchyma cells Tracheids and vessels (colorized SEM) 80 µm Vessel element Vessel elements with perforated end walls Tracheids SUGAR-CONDUCTING CELLS OF THE PHLOEM Collenchyma cells (in cortex of Sambucus, elderberry; cell walls stained red) (LM) Sieve-tube members: longitudinal view (LM) SCLERENCHYMA CELLS 5 µm Companion cell Sclereid cells in pear (LM) Sieve-tube member 25 µm Plasmodesma Sieve plate Cell wall Nucleus Cytoplasm Companion cell 30 µm 15 µm Fiber cells (transverse section from ash tree) (LM) Sieve-tube members: longitudinal view Sieve plate with pores (LM)

  34. Concept 35.2: Meristems generate cells for new organs • Apical meristems are located at the tips of roots and in the buds of shoots • Apical meristems elongate shoots and roots, a process called primary growth

  35. Lateral meristems add thickness to woody plants, a process called secondary growth • There are two lateral meristems: the vascular cambium and the cork cambium • The vascular cambium adds layers of vascular tissue called secondary xylem (wood) and secondary phloem • The cork cambium replaces the epidermis with periderm, which is thicker and tougher

  36. LE 35-10 Primary growth in stems Shoot apical meristems (in buds) Epidermis Cortex Primary phloem Primary xylem Vascular cambium Lateral meristems Pith Cork cambium Secondary growth in stems Periderm Cork cambium Pith Cortex Primary xylem Primary phloem Secondary xylem Root apical meristems Secondary phloem Vascular cambium

  37. LE 35-11 Terminal bud Bud scale Axillary buds Leaf scar This year’s growth (one year old) Node Stem Internode One-year-old side branch formed from axillary bud near shoot apex Leaf scar Last year’s growth (two years old) Scars left by terminal bud scales of previous winters Growth of two years ago (three years old) Leaf scar

  38. Concept 35.3: Primary growth lengthens roots and shoots • Primary growth produces the primary plant body, the parts of the root and shoot systems produced by apical meristems

  39. Primary Growth of Roots • The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil • Growth occurs just behind the root tip, in three zones of cells: • Zone of cell division • Zone of elongation • Zone of maturation Video: Root Growth in a Radish Seed (time lapse)

  40. LE 35-12 Vascular cylinder Cortex Epidermis Key Zone of maturation Root hair Dermal Ground Vascular Zone of elongation Apical meristem Zone of cell division Root cap 100 µm

  41. The primary growth of roots produces the epidermis, ground tissue, and vascular tissue • In most roots, the stele is a vascular cylinder • The ground tissue fills the cortex, the region between the vascular cylinder and epidermis • The innermost layer of the cortex is called the endodermis

  42. LE 35-13 Epidermis Cortex Vascular cylinder Endodermis Pericycle Core of parenchyma cells Xylem Phloem 100 µm 100 µm Transverse section of a typical root. In the roots of typical gymnosperms and eudicots, as well as some monocots, the stele is a vascular cylinder consisting of a lobed core of xylem with phloem between the lobes. Transverse section of a root with parenchyma in the center. The stele of many monocot roots is a vascular cylinder with a core of parenchyma surrounded by a ring of alternating xylem and phloem. Endodermis Key Dermal Pericycle Ground Vascular Xylem Phloem 50 µm

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