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 Vegetative shoot Blade Petiole Stem Leaf Taproot Lateral roots Root system Shoot system Axillary bud 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 (d) Buttress roots (e) Pneumatophores 4

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 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. (d) 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. (c) 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. (b) 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. (a) Storage leaves Stem Root Node Rhizome 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 Vascular tissue 10

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. 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

XylemPhloem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Epidermis Vascular bundle Cortex Key Dermal Ground Vascular 1 mm (a)A dicot stem. 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

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

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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 Dermal Ground Vascular Key Cortex Vascular cylinder Epidermis Root hair Zone of maturation Zone of elongation Zone of cell division Apical meristem Root cap 100  m 23

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 Apical meristemLeaf primordia Developing vascular strand Axillary bud meristems 0.25 mm 24

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 In woody plants, there are lateral meristems that add secondary growth, increasing the girth of roots and stems. Apical meristems add primary growth, or growth in length. Vascular cambium Cork cambium Lateral meristems Root apical meristems Primary growth in stems Epidermis Cortex Primary phloem Primary xylem Pith Secondary growth in stems Periderm Cork cambium Cortex Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Pith Shoot apical meristems (in buds) The cork cambium adds secondary dermal tissue. The vascular cambium adds secondary xylem and phloem. 26

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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. 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 elementXylem 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