Plant Three basic organs evolved roots stems and
Plant • Three basic organs evolved: roots, stems, and leaves • They are organized into a root system and a shoot system Reproductive shoot (flower) Terminal bud Node Internode Terminal bud Shoot system Vegetative shoot Leaf Blade Petiole Axillary bud Stem Taproot Lateral roots Root system 1
Roots • A root – Is an organ that anchors the vascular plant – Absorbs minerals and water – Often stores organic nutrients 2
• 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 3
Many plants have modified roots (a) Prop roots (b) Storage roots (c) “Strangling” aerial roots 4 (d) Buttress roots (e) Pneumatophores
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 5
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 6
Many plants have modified stems (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) Stem 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. Root Node (b) 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. (c) Rhizome 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 7
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 8
Some plant species Have evolved modified leaves that serve various functions (a) Tendrils. The tendrils by which this pea 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. 9
The Three Tissue Systems: Dermal, Vascular, and Ground • Each plant organ – Has dermal, vascular, and ground tissues Dermal tissue Ground tissue 10 Vascular tissue
• The dermal tissue system – Consists of the epidermis and periderm • The vascular tissue system –Carries out long-distance transport of materials between roots and shoots –Consists of two tissues, xylem and phloem • Ground tissue –Includes various cells specialized for functions such as storage, photosynthesis, and support 11
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 12
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 13
In most monocot stems The vascular bundles are scattered throughout the ground tissue, rather than forming a ring Ground tissue Epidermis Vascular bundles 1 mm A monocot stem (maize) with vascular bundles scattered throughout the ground tissue. In such an arrangement, ground tissue is not partitioned into pith and cortex. (LM of transverse section) 14
Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Key Cortex Epidermis Dermal Ground Vascular bundle Vascular 1 mm (a) A dicot stem (sunflower), with vascular bundles forming a ring. Ground tissue toward the inside is called pith, and ground tissue toward the outside is called cortex. (LM of transverse section) 15
Difference in monocot and dicot 16
Leaf anatomy Guard cells Key to labels Dermal Ground Stomatal pore Vascular Cuticle Epidermal cell Sclerenchyma fibers 50 µm (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Stoma Upper epidermis Palisade mesophyll Bundlesheath cell Spongy mesophyll Lower epidermis Guard cells Cuticle Vein Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Air spaces Guard cells (c) Transverse section of a lilac 100 µm 17 (Syringa) leaf (LM)
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Tissue Organization of Leaves • The epidermal barrier in leaves – Is interrupted by stomata, which allow CO 2 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
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 Cortex Vascular cylinder Epidermis Key Root hair Dermal Zone of maturation Ground Vascular Zone of elongation Apical meristem Zone of cell division Root cap 23 100 m
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 leafbearing nodes Apical meristem Leaf primordia Developing vascular strand Axillary bud meristems 24 0. 25 mm
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
An overview of primary and secondary growth Primary growth in stems Shoot apical meristems (in buds) Epidermis Cortex Primary phloem In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems. Vascular cambium Cork cambium Primary xylem Lateral meristems Pith Secondary growth in stems Apical meristems add primary growth, or growth in length. Pith Primary xylem Root apical meristems Secondary xylem Periderm Cork cambium The cork cambium adds secondary dermal tissue. Cortex Primary phloem The vascular cambium adds Secondary secondary 26 phloem xylem and Vascular cambium phloem.
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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. 28
Pattern of lignin in xylem vessels 29
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 30
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. 31
• 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. 32
Xylem vessel element Xylem Tracheid 33
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• • This is a file from the Wikimedia Commons 35
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. 36
Phototropism • Is growth response or movement of a plant in response to light coming from a specific direction. • +ve phototropism • -ve phototropism 37
Plant Hormones • • Auxin Indole-3 -acetic acid Works together with other hormones. Gibberellins Abscisic Acid Ethylene Cytokinins 38
Two shoots-one in dark and other was exposed to blue light 39
Second experiment- covering the tip with foil 40
• Mica is impermeable • Both plants grew straight Conclusion. Chemical compd. is produced in tip, transported down Mica is blocking Tip is the source 41
Block of agar used plant grew towards the light -block of agar used -plant grew towards the light -Auxin was able to diffuse thru the agar 42
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 43
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