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The plant body has a hierarchy of organs, tissues, and cells
Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells
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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
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Three basic organs evolved: roots, stems, and leaves
They are organized into a root system and a shoot system Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system
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Reproductive shoot (flower)
Fig. 35-2 Reproductive shoot (flower) Apical bud Node Internode Apical bud Shoot system Vegetative shoot Blade Leaf Petiole Axillary bud Stem Figure 35.2 An overview of a flowering plant Taproot Lateral branch roots Root system
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Roots are multicellular organs with important functions:
Anchoring the plant Absorbing minerals and water Storing organic nutrients
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Seedless vascular plants and monocots have a fibrous root system characterized by thin lateral roots with no main root A taproot system consists of one main vertical root that gives rise to lateral roots, or branch roots Adventitious roots arise from stems or leaves
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Roots grow from their tips
In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area
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Plants grow for a lifetime
The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil
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Meristematic ( meristem) are perpetually embryonic tissue and allow for indeterminate growth – found at tips of root/shoots Apical meristems (Zone of cell division ) area where mitosis occurs Apical meristems elongate shoots and roots, a process called primary growth
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Shoot tip (shoot apical meristem and young leaves) Vascular cambium
Fig. 35-UN1 Shoot tip (shoot apical meristem and young leaves) Vascular cambium Lateral meristems Cork cambium Axillary bud meristem Root apical meristems
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Primary Growth of Roots
Growth occurs just behind the root tip, in three zones of cells: Zone of elongation – expands cells, pushes root downward Zone of maturation- specializes, forms root hairs Zone of cell division – apical meristem area Video: Root Growth in a Radish Seed (Time Lapse)
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Cortex Vascular cylinder Epidermis Key to labels Zone of
Fig Cortex Vascular cylinder Epidermis Key to labels Zone of differentiation Root hair Dermal Ground Vascular Zone of elongation Figure Primary growth of a root Apical meristem Zone of cell division Root cap 100 µm
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The primary growth of roots produces the epidermis, cortex (ground tissue), and vascular tissue
The epidermis is a single layer of tightly packed cells The ground tissue fills the cortex, store food In most roots, (the stele) is a vascular cylinder that is the xylem and phloem Xylem moves water/minerals, phloem moves food
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Root with xylem and phloem in the center (typical of eudicots)
Fig a1 Epidermis Key to labels Cortex Dermal Endodermis Ground Vascular Vascular cylinder Pericycle Figure Organization of primary tissues in young roots Xylem 100 µm Phloem (a) Root with xylem and phloem in the center (typical of eudicots)
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Fig. 35-3 Figure 35.3 Root hairs of a radish seedling
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Fig. 35-4a Figure 35.4 Modified roots Prop roots
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Fig. 35-4b Figure 35.4 Modified roots Storage roots
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“Strangling” aerial roots
Fig. 35-4c Figure 35.4 Modified roots “Strangling” aerial roots
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Fig. 35-4d Figure 35.4 Modified roots Pneumatophores
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Fig. 35-4e Figure 35.4 Modified roots Buttress roots
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Stems Vascular plumbing, move from roots, stem then leaf veins Young plants are green or herbaceous Perennials live for many years Older plants can be herbaceous/woody Annuals complete their life cycle in a year or less Biennials require two growing seasons A plant can grow throughout its life; this is called indeterminate growth
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Century Plant . Legend says the century plant takes one hundred years to bloom. However, century plants in cultivation may bloom much quicker. The century plant uses all of its energy to produce this once-in-a-lifetime bloom. The flower spike, growing at the incredible rate of 5–6 inches per day, and can reached heights of 30 to 35 feet. (Longwood gardens)
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Stems functions Hold up leaves
Conduct substances between roots and leaves
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Apical bud Bud scale Axillary buds This year’s growth (one year old)
Fig Apical bud Bud scale Axillary buds This year’s growth (one year old) Leaf scar Bud scar Node One-year-old side branch formed from axillary bud near shoot tip Internode Last year’s growth (two years old) Leaf scar Figure Three years’ growth in a winter twig Stem Bud scar left by apical bud scales of previous winters Growth of two years ago (three years old) Leaf scar
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An apical bud, or terminal bud, is located near the shoot tip (meristematic tissue) and causes elongation of a young shoot and can make a leaf or flower When the bud falls off it leaves a bud scale scar, when the leaf falls off it forms a leaf scar Little white dots are called lenticles which allow for gas exchange
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How do you find the age of a tree ?
You can look at the stem… later will look at a cross section of a tree trunk
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A stem is an organ consisting of
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
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Many plants have modified stems
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Corm Underground stem ,short, thick, fleshy ex- crocus
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Bulb fleshy leaves Storage leaves Stem Fig. 35-5b
Figure 35.5 Modified stems Stem Bulb fleshy leaves
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Rhizomes grows horizontally under/on ground
Fig. 35-5a Figure 35.5 Modified stems Rhizomes grows horizontally under/on ground
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Tubers swollen underground stem
Fig. 35-5d Figure 35.5 Modified stems Tubers swollen underground stem
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Stolons horizontal along the surface, stem dies
Fig. 35-5c Stolon Figure 35.5 Modified stems Stolons horizontal along the surface, stem dies
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Leaves The leaf is the main photosynthetic organ of most vascular plants node joins the leaf to a stem Leaves generally consist of a flattened blade and a stalk called the petiole Petiole connects the stem to the blade
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Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves
Most monocots have parallel veins Most eudicots have branching veins In classifying angiosperms, taxonomists may use leaf morphology as a criterion
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Tendrils specialized stem, leaf , petiole
Fig. 35-7a Figure 35.7 Modified leaves Tendrils specialized stem, leaf , petiole
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Spines modified leaf conserves water
Fig. 35-7b Figure 35.7 Modified leaves Spines modified leaf conserves water
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Fig. 35-7c Figure 35.7 Modified leaves Storage leaves
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Fig. 35-7d Figure 35.7 Modified leaves Reproductive leaves
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Bracts brightly colored leaves
Fig. 35-7e Figure 35.7 Modified leaves Bracts brightly colored leaves
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Common Types of Plant Cells
Like any multicellular organism, a plant is characterized by cellular differentiation, the specialization of cells in structure and function
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Some major types of plant cells:
Parenchyma Collenchyma Sclerenchyma Water-conducting cells of the xylem Sugar-conducting cells of the phloem
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BioFlix: Tour of a Plant Cell
Parenchyma Cells Mature parenchyma cells Have thin and flexible walls Perform the most metabolic functions such as photosynthesis, and store sugar BioFlix: Tour of a Plant Cell
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Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm
Fig a Figure Examples of differentiated plant cells Parenchyma cells in Elodea leaf, with chloroplasts (LM) 60 µm
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Collenchyma Cells Collenchyma cells help support young parts of the plant shoot They have thicker cell walls flexible support without restraining growth
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Collenchyma cells (in Helianthus stem) (LM)
Fig b 5 µm Figure Examples of differentiated plant cells Collenchyma cells (in Helianthus stem) (LM)
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Sclerenchyma Cells Sclerenchyma cells are rigid because of thick walls strengthened with lignin (Lignin is A complex polymer, constituent of wood, that binds to cellulose fibers and hardens and strengthens the cell walls of plants.) They are dead at functional maturity There are two types: Fibers are long and slender and arranged in threads Sclereids are short and irregular in shape and have very thick lignified secondary walls
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Sclereid cells in pear (LM)
Fig c 5 µm Sclereid cells in pear (LM) 25 µm Cell wall Figure Examples of differentiated plant cells Fiber cells (cross section from ash tree) (LM)
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Tissues in Primary Growth
Each plant organ has dermal, vascular, and ground tissues Each of these three categories forms a tissue system
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In nonwoody plants, the dermal tissue system consists of the epidermis
Protects young plants A waxy coating called the cuticle helps prevent water loss from the epidermis
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The vascular tissue system carries out long-distance transport between roots and shoots
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
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Tissues that are neither dermal nor vascular are the ground tissue system
Storage in root, stem and leaf for storage, photosynthesis, and support
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Dermal tissue Ground tissue Vascular tissue Fig. 35-8
Figure 35.8 The three tissue systems Dermal tissue Ground tissue Vascular tissue
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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 cork cells
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The Cork Cambium and the Production of Periderm
The cork cambium gives rise to the secondary plant body’s protective covering, or periderm Periderm consists of the cork cambium plus the layers of cork cells it produces Bark consists of all the tissues external to the vascular cambium, including secondary phloem and periderm
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Cross section of a three-year- old Tilia (linden) stem (LM)
Fig b Secondary phloem Bark Vascular cambium Cork cambium Late wood Secondary xylem Periderm Early wood Cork 0.5 mm Figure Primary and secondary growth of a stem Vascular ray Growth ring (b) Cross section of a three-year- old Tilia (linden) stem (LM) 0.5 mm
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Fig Figure Is this tree living or dead?
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Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age
Dendrochronology is the analysis of tree ring growth patterns, and can be used to study past climate change
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Secondary xylem accumulates as wood
Early wood, formed in the spring, has thin cell walls to maximize water delivery Late wood, formed in late summer, has thick-walled cells and contributes more to stem support
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As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals The outer layers, known as sapwood, still transport materials through the xylem Older secondary phloem sloughs off and does not accumulate
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Growth ring Vascular ray Heartwood Secondary xylem Sapwood
Fig Growth ring Vascular ray Heartwood Secondary xylem Sapwood Fig Anatomy of a tree trunk Vascular cambium Secondary phloem Bark Layers of periderm
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Leaves on trees are identified by arrangement veins attachment
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Leaf Arrangement Petiole (a) Simple leaf Axillary bud Leaflet (b)
Fig. 35-6 Leaf Arrangement Petiole (a) Simple leaf Axillary bud Leaflet (b) Compound leaf Petiole Axillary bud Figure 35.6 Simple versus compound leaves (c) Doubly compound leaf Leaflet Petiole Axillary bud
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Leaf Veins
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Leaf Attachment
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Tissue Organization of Leaves
The epidermis has a waxy outer covering called a cuticle Epidermis protects from injury and drying out stomata allows CO2 exchange between the air and the photosynthetic cells in a leaf
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(a) Cutaway drawing of leaf tissues
Fig a Key to labels Dermal Ground Cuticle Sclerenchyma fibers Vascular Stoma Upper epidermis Palisade mesophyll Bundle- sheath cell Spongy mesophyll Figure Leaf anatomy Lower epidermis Cuticle Xylem Phloem Vein Guard cells (a) Cutaway drawing of leaf tissues
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Palisade Layer- long narrow cells ,ground tissue , chloroplast packet in
Spongy layer (Mesophyll) is ground tissue with air space, gas exchange ,chloroplasts Each stomata pore is flanked by two guard cells, which regulate its opening and closing for gas exchange
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Surface view of a spiderwort (Tradescantia) leaf (LM)
Fig b Guard cells Stomatal pore 50 µm Epidermal cell Figure Leaf anatomy (b) Surface view of a spiderwort (Tradescantia) leaf (LM)
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Fig. 35-18 Figure 35.18 Leaf anatomy Guard cells Key to labels
Stomatal pore 50 µm Dermal Epidermal cell Ground Cuticle Sclerenchyma fibers Vascular Stoma (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Palisade mesophyll Bundle- sheath cell Spongy mesophyll Figure Leaf anatomy Lower epidermis 100 µm Cuticle Xylem Phloem Vein Guard cells Vein Air spaces Guard cells (a) Cutaway drawing of leaf tissues (c) Cross section of a lilac (Syringa)) leaf (LM)
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The vascular tissue of each leaf is continuous with the vascular tissue of the stem
Veins are the leaf’s vascular bundles and function as the leaf’s skeleton Each vein in a leaf is enclosed by a protective bundle sheath
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Cross section of a lilac (Syringa) leaf (LM)
Fig c Upper epidermis Key to labels Palisade mesophyll Dermal Ground Vascular Spongy mesophyll Lower epidermis 100 µm Figure Leaf anatomy Vein Air spaces Guard cells (c) Cross section of a lilac (Syringa) leaf (LM)
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Root with parenchyma in the center (typical of monocots)
Fig b Epidermis Cortex Endodermis Vascular cylinder Key to labels Pericycle Dermal Core of parenchyma cells Ground Vascular Figure Organization of primary tissues in young roots Xylem Phloem 100 µm (b) Root with parenchyma in the center (typical of monocots)
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Cross section of stem with vascular bundles forming
Fig a Phloem Xylem Sclerenchyma (fiber cells) Ground tissue connecting pith to cortex Pith Figure Organization of primary tissues in young stems Key to labels Epidermis Cortex Dermal Vascular bundle Ground 1 mm Vascular (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots)
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Cross section of stem with scattered vascular bundles
Fig b Ground tissue Epidermis Key to labels Figure Organization of primary tissues in young stems Vascular bundles Dermal Ground Vascular 1 mm (b) Cross section of stem with scattered vascular bundles (typical of monocots)
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Preprophase bands of microtubules
Fig Preprophase bands of microtubules 10 µm Figure The preprophase band and the plane of cell division Nuclei Cell plates
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Fig. 35-UN3
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