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Plant

Reproductive shoot (flower). Terminal bud. Node. Internode. Terminal bud. Shoot system. Vegetative shoot. Blade Petiole. Leaf. Axillary bud. Stem. Taproot. Root system. Lateral roots. Plant. Three basic organs evolved: roots, stems, and leaves

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Plant

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

  2. Roots • A root • Is an organ that anchors the vascular plant • Absorbs minerals and water • Often stores organic nutrients

  3. In most plants • The absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the root

  4. (c) “Strangling” aerialroots (a) Prop roots (b) Storage roots (d) Buttress roots (e) Pneumatophores Many plants have modified roots

  5. 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

  6. Buds • 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

  7. (a) Stolons. Shown here on a strawberry plant, stolons are horizontal stems that grow along the surface. These “runners” enable a plant to reproduce asexually, as plantlets form at nodes along each runner. Storage leaves (d) Rhizomes. The edible base of this ginger plant is an example of a rhizome, a horizontal stem that grows just below the surface or emerges and grows along the surface. Stem Node Root (b) Bulbs. Bulbs are vertical, underground shoots consisting mostly of the enlarged bases of leaves that store food. You can see the many layers of modified leaves attached to the short stem by slicing an onion bulb lengthwise. Rhizome (c) Tubers. Tubers, such as these red potatoes, are enlarged ends of rhizomes specialized for storing food. The “eyes” arranged in a spiral pattern around a potato are clusters of axillary buds that mark the nodes. Root Many plants have modified stems

  8. 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

  9. (a) Tendrils. The tendrils by which thispea plant clings to a support are modified leaves. After it has “lassoed” a support, a tendril forms a coil that brings the plant closer to the support. Tendrils are typically modified leaves, but some tendrils are modified stems, as in grapevines. (b) Spines. The spines of cacti, such as this prickly pear, are actually leaves, and photosynthesis is carried out mainly by the fleshy green stems. (c) Storage leaves. Most succulents, such as this ice plant, have leaves modified for storing water. (d) Bracts. Red parts of the poinsettia are often mistaken for petals but are actually modified leaves called bracts that surround a group of flowers. Such brightly colored leaves attract pollinators. (e) Reproductive leaves. The leaves of some succulents, such as Kalanchoe daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil. Some plant speciesHave evolved modified leaves that serve various functions

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

  11. The vascular tissue system • Carries out long-distance transport of materials between roots and shoots • Consists of two tissues, xylem and phloem • The dermal tissue system • Consists of the epidermis and periderm • Ground tissue • Includes various cells specialized for functions such as storage, photosynthesis, and support

  12. Common Types of Plant Cells • Like any multicellular organism • A plant is characterized by cellular differentiation, the specialization of cells in structure and function • Some of the major types of plant cells include • Parenchyma • Collenchyma • Sclerenchyma • Water-conducting cells of the xylem • Sugar-conducting cells of the phloem

  13. Vascular tissue • 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

  14. Groundtissue Epidermis Vascularbundles 1 mm A monocot stem. A monocot stem (maize) with vascularbundles scattered throughout the ground tissue. In such anarrangement, ground tissue is not partitioned into pith andcortex. (LM of transverse section) In most monocot stemsThe vascular bundles are scattered throughout the ground tissue, rather than forming a ring

  15. Phloem Xylem Sclerenchyma(fiber cells) Ground tissueconnecting pith to cortex Pith Key Cortex Epidermis Dermal Ground Vascularbundle Vascular 1 mm (a) A dicot stem. A dicot stem (sunflower), withvascular bundles forming a ring. Ground tissue towardthe inside is called pith, and ground tissue toward theoutside is called cortex. (LM of transverse section)

  16. Difference in monocot and dicot

  17. Leaf anatomy Guard cells Key to labels Dermal Stomatal pore Ground Vascular Epidermal cell Sclerenchyma fibers 50 µm Cuticle (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Stoma Upper epidermis Palisade mesophyll Bundle- sheath cell Spongy mesophyll Lower epidermis Guard cells Cuticle Vein Xylem Vein Air spaces Guard cells Guard cells Phloem 100 µm Transverse section of a lilac (Syringa) leaf (LM) (c) (a) Cutaway drawing of leaf tissues

  18. Tissue Organization of Leaves • The epidermal barrier in leaves • Is interrupted by stomata, which allow CO2 exchange between the surrounding air and the photosynthetic cells within a leaf • The ground tissue in a leaf • Is sandwiched between the upper and lower epidermis • The vascular tissue of each leaf • Is continuous with the vascular tissue of the stem

  19. Meristems in Dicotyledonous plant • Meristems generate cells for new organs • Apical meristems • Are located at the tips of roots and in the buds of shoots • Elongate shoots and roots through primary growth

  20. Lateral meristems • Add thickness to woody plants through secondary growth

  21. APICAL MERISTEM • 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

  22. Cortex Vascular cylinder Epidermis Key Zone of maturation Root hair Dermal Ground Vascular Zone of elongation Apical meristem Zone of cell division Root cap 100 m Primary Growth of Roots • The root tip is covered by a root cap, which protects the delicate apical meristem as the root pushes through soil during primary growth

  23. Apical meristem Leaf primordia Developing vascular strand Axillary bud meristems 0.25 mm Primary Growth of Shoots • A shoot apical meristem • Is a dome-shaped mass of dividing cells at the tip of the terminal bud • Gives rise to a repetition of internodes and leaf-bearing nodes

  24. Secondary growth • Secondary growth • Occurs in stems and roots of woody plants but rarely in leaves • The secondary plant body • Consists of the tissues produced by the vascular cambium and cork cambium

  25. Primary growth in stems Shoot apical meristems (in buds) Epidermis Cortex In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems. Primary phloem Primary xylem Vascular cambium Lateral meristems Pith Cork cambium Secondary growth in stems Apical meristems add primary growth, or growth in length. Periderm Cork cambium Pith The cork cambium adds secondary dermal tissue. Primary xylem Cortex Primary phloem Root apical meristems Secondary xylem The vascular cambium adds secondary xylem and phloem. Secondary phloem Vascular cambium An overview of primary and secondary growth

  26. Xylem Xylem vessels - heavily lignified to withstand the pressure of carrying water. • Dead and hollow so minimum resistance for water flow. • Stacked on end to end, with no end walls. • Perforated with holes where there used to be plasmodesmata, for sideways/radial transport. • Transport of water and mineral ions dissolved in water.

  27. Pattern of lignin in xylem vessels

  28. Tracheids • Tracheids - similar to xylem vessels, • heavily lignified, • Dead, • tapering ends so water only passed sideways through the holes. • Fibres - heavily lignified, only for support. • Xylem parenchyma - normal metabolic activity of the cell, packing tissue. - Involved in radial transport. Alive, with cellulose cell walls. May store starch

  29. Phloem • Phloem sieve tube element - alive, but with only a thin cytoplasmic strand along the sides • no Golgi Apparatus, nucleus or ribosomes. • Stacked on end to end, end walls are modified to form sieve tube plates with pores in them. • Transport of organic solutes such as sucrose, amino acids. • Companion cells - usually one per sieve tube element, fully functional cell with lots of mitochondria.

  30. Involved in translocation by unloading/loading sucrose into the sieve tube element and for metabolic support. • Linked to the sieve tube element by plasmodesmata. • Phloem fibre - same as xylem fibre • Phloem parenchyma - same as xylem parenchyma.

  31. Xylem vessel element Xylem Tracheid

  32. This is a file from the Wikimedia Commons

  33. summary • In dicot stems, the cambium layer gives rise to phloem cells on the outside and xylem cells on the inside. • All the tissue from the cambium layer outward is considered bark, • while all the tissue inside the cambium layer to the center of the tree is wood.

  34. Phototropism • Is growth response or movement of a plant in response to light coming from a specific direction. • +ve phototropism • -ve phototropism

  35. Plant Hormones • Auxin • Indole-3-acetic acid • Works together with other hormones- • Gibberellins • Abscisic Acid • Ethylene • Cytokinins

  36. Two shoots-one in dark and other was exposed to blue light

  37. Second experiment- covering the tip with foil

  38. Mica is impermeable • Both plants grew straight Conclusion- Chemical compd. is produced in tip, transported down Mica is blocking Tip is the source

  39. Block of agar usedplant grew towards the light -block of agar used-plant grew towards the light -Auxin was able to diffuse thru the agar

  40. AUXIN • Produced in apical bud • Transported down the stem • Accumulates at the shaded side of the plant • Stimulate growth- cell division and cell stretching. • Plants grow towards light

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