Plant Structure, Growth, and Development Chapter 35 Plant Structure, Growth, and Development

Concept 35.1: Plants have a hierarchical organization consisting of organs, tissues, and cells Plants have organs composed of different tissues, which in turn are composed of different cell types A tissue is a group of cells consisting of one or more cell types that together perform a specialized function An organ consists of several types of tissues that together carry out particular functions © 2011 Pearson Education, Inc.

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 Plants take up water and minerals from below ground Plants take up CO2 and light from above ground © 2011 Pearson Education, Inc.

Three basic organs evolved: roots, stems, and leaves They are organized into a root system and a shoot system © 2011 Pearson Education, Inc.

Reproductive shoot (flower) Figure 35.2 Reproductive shoot (flower) Apical bud Node Internode Apical bud Shoot system Vegetative shoot Axillary bud Blade Leaf Petiole Stem Figure 35.2 An overview of a flowering plant. Taproot Root system Lateral (branch) roots

Monocots and eudicots are the two major groups of angiosperms Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system Monocots and eudicots are the two major groups of angiosperms © 2011 Pearson Education, Inc.

Roots A root is an organ with important functions: Anchoring the plant Absorbing minerals and water Storing carbohydrates © 2011 Pearson Education, Inc.

Most monocots have a fibrous root system, which consists of: Most eudicots and gymnosperms have a taproot system, which consists of: A taproot, the main vertical root Lateral roots, or branch roots, that arise from the taproot Most monocots have a fibrous root system, which consists of: Adventitious roots that arise from stems or leaves Lateral roots that arise from the adventitious roots © 2011 Pearson Education, Inc.

In most plants, absorption of water and minerals occurs near the root hairs, where vast numbers of tiny root hairs increase the surface area © 2011 Pearson Education, Inc.

Figure 35.3 Figure 35.3 Root hairs of a radish seedling.

Figure 35.4a Figure 35.4 Evolutionary adaptations of roots. Prop roots

Figure 35.4b Storage roots Figure 35.4 Evolutionary adaptations of roots.

“Strangling” aerial roots Figure 35.4c Figure 35.4 Evolutionary adaptations of roots. “Strangling” aerial roots

Pneumatophores Figure 35.4d Figure 35.4 Evolutionary adaptations of roots. Pneumatophores

Buttress roots Figure 35.4e Figure 35.4 Evolutionary adaptations of roots. Buttress roots

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 © 2011 Pearson Education, Inc.

Apical dominance helps to maintain dormancy in most axillary buds An axillary bud is a structure that has the potential to form a lateral shoot, or branch An apical bud, or terminal bud, is located near the shoot tip and causes elongation of a young shoot Apical dominance helps to maintain dormancy in most axillary buds © 2011 Pearson Education, Inc.

Many plants have modified stems (e. g Many plants have modified stems (e.g., rhizomes, bulbs, stolons, tubers) © 2011 Pearson Education, Inc.

Rhizome Root Rhizomes Figure 35.5a Figure 35.5 Evolutionary adaptations of stems. Rhizomes

Storage leaves Stem Bulbs Figure 35.5b Figure 35.5 Evolutionary adaptations of stems. Stem Bulbs

Stolon Stolons Figure 35.5c Figure 35.5 Evolutionary adaptations of stems. Stolons

Figure 35.5d Figure 35.5 Evolutionary adaptations of stems. Tubers

Leaves The leaf is the main photosynthetic organ of most vascular plants Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Simple leaf Axillary bud Petiole Compound leaf Doubly compound leaf Figure 35.6 Simple leaf Axillary bud Petiole Compound leaf Doubly compound leaf Leaflet Figure 35.6 Simple versus compound leaves. Petiole Axillary bud Axillary bud Petiole Leaflet

Some plant species have evolved modified leaves that serve various functions © 2011 Pearson Education, Inc.

Tendrils Spines Storage leaves Reproductive leaves Bracts Figure 35.7 Figure 35.7 Evolutionary adaptations of leaves. Bracts

Dermal, Vascular, and Ground Tissues Each plant organ has dermal, vascular, and ground tissues Each of these three categories forms a tissue system Each tissue system is continuous throughout the plant © 2011 Pearson Education, Inc.

Dermal tissue Ground tissue Vascular tissue Figure 35.8 Figure 35.8 The three tissue systems. Dermal tissue Ground tissue Vascular tissue

In nonwoody plants, the dermal tissue system consists of the epidermis A waxy coating called the cuticle helps prevent water loss from the epidermis In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots Trichomes are outgrowths of the shoot epidermis and can help with insect defense © 2011 Pearson Education, Inc.

The two vascular tissues are xylem and phloem 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 © 2011 Pearson Education, Inc.

The vascular tissue of a stem or root is collectively called the stele In angiosperms the stele of the root is a solid central vascular cylinder The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem © 2011 Pearson Education, Inc.

Tissues that are neither dermal nor vascular are the ground tissue system Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex Ground tissue includes cells specialized for storage, photosynthesis, and support © 2011 Pearson Education, Inc.

Concept 35.2: Meristems generate cells for primary and secondary growth A plant can grow throughout its life; this is called indeterminate growth Some plant organs cease to grow at a certain size; this is called determinate growth © 2011 Pearson Education, Inc.

Meristems are perpetually embryonic tissue and allow for indeterminate growth Apical meristems are located at the tips of roots and shoots and at the axillary buds of shoots Apical meristems elongate shoots and roots, a process called primary growth © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Primary growth in stems Figure 35.11 Primary growth in stems Epidermis Cortex Primary phloem Shoot tip (shoot apical meristem and young leaves) Primary xylem Pith Vascular cambium Secondary growth in stems Cork cambium Lateral meristems Cork cambium Axillary bud meristem Cortex Periderm Primary phloem Figure 35.11 An overview of primary and secondary growth. Pith Secondary phloem Root apical meristems Primary xylem Vascular cambium Secondary xylem

This year’s growth (one year old) Leaf scar Figure 35.12 Apical bud Bud scale Axillary buds This year’s growth (one year old) Leaf scar Node Bud scar One-year-old side branch formed from axillary bud near shoot tip Internode Last year’s growth (two year old) Leaf scar Stem Figure 35.12 Three years’ growth in a winter twig. Bud scar Growth of two years ago (three years old) Leaf scar

Flowering plants can be categorized based on the length of their life cycle Annuals complete their life cycle in a year or less Biennials require two growing seasons Perennials live for many years © 2011 Pearson Education, Inc.

Concept 35.3: Primary growth lengthens roots and shoots Primary growth produces the parts of the root and shoot systems produced by apical meristems © 2011 Pearson Education, Inc.

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 differentiation, or maturation © 2011 Pearson Education, Inc.

Zone of differentiation Ground Root hair Vascular Figure 35.13 Cortex Vascular cylinder Key to labels Epidermis Dermal Zone of differentiation Ground Root hair Vascular Zone of elongation Figure 35.13 Primary growth of a root. Zone of cell division (including apical meristem) Mitotic cells 100 m Root cap

In angiosperm roots, the stele is a vascular cylinder The primary growth of roots produces the epidermis, ground tissue, and vascular tissue In angiosperm roots, the stele is a vascular cylinder In most eudicots, the xylem is starlike in appearance with phloem between the “arms” In many monocots, a core of parenchyma cells is surrounded by rings of xylem then phloem © 2011 Pearson Education, Inc.

Core of parenchyma cells Figure 35.14 Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem 100 m Phloem 100 m (a) Root with xylem and phloem in the center (typical of eudicots) (b) Root with parenchyma in the center (typical of monocots) 50 m Key to labels Figure 35.14 Organization of primary tissues in young roots. Endodermis Pericycle Dermal Xylem Ground Phloem Vascular

Root with xylem and phloem in the center (typical of eudicots) Figure 35.14aa Epidermis Key to labels Cortex Endodermis Dermal Vascular cylinder Ground Vascular Pericycle Xylem Phloem Figure 35.14 Organization of primary tissues in young roots. 100 m (a) Root with xylem and phloem in the center (typical of eudicots)

50 m Endodermis Pericycle Xylem Phloem Key to labels Dermal Ground Figure 35.14ab 50 m Endodermis Pericycle Xylem Phloem Key to labels Figure 35.14 Organization of primary tissues in young roots. Dermal Ground Vascular

Core of parenchyma cells Figure 35.14b Epidermis Key to labels Cortex Dermal Endodermis Ground Vascular Vascular cylinder Pericycle Core of parenchyma cells Figure 35.14 Organization of primary tissues in young roots. Xylem Phloem 100 m (b) Root with parenchyma in the center (typical of monocots)

Tissue Organization of Stems Lateral shoots develop from axillary buds on the stem’s surface In most eudicots, the vascular tissue consists of vascular bundles arranged in a ring © 2011 Pearson Education, Inc.

Sclerenchyma (fiber cells) Ground tissue Figure 35.17 Phloem Xylem Sclerenchyma (fiber cells) Ground tissue Ground tissue connecting pith to cortex Pith Epidermis Key to labels Epidermis Cortex Vascular bundles Figure 35.17 Organization of primary tissues in young stems. Vascular bundle Dermal 1 mm 1 mm Ground (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots) (b) Vascular Cross section of stem with scattered vascular bundles (typical of monocots)

Tissue Organization of Leaves The epidermis in leaves is interrupted by stomata, which allow CO2 and O2 exchange between the air and the photosynthetic cells in a leaf Each stomatal pore is flanked by two guard cells, which regulate its opening and closing The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis © 2011 Pearson Education, Inc.

Each vein in a leaf is enclosed by a protective bundle sheath 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 © 2011 Pearson Education, Inc.

Surface view of a spiderwort (Tradescantia) leaf (LM) Cuticle Stoma Figure 35.18 Guard cells Key to labels Stomatal pore Dermal Ground Epidermal cell 50 m Vascular Sclerenchyma fibers (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Cuticle Stoma Upper epidermis Palisade mesophyll Spongy mesophyll Bundle- sheath cell Figure 35.18 Leaf anatomy. Lower epidermis 100 m Xylem Vein Cuticle Phloem Guard cells Guard cells Vein Air spaces (a) Cutaway drawing of leaf tissues (c) Cross section of a lilac (Syringa) leaf (LM)

Growth ring Vascular ray Heartwood Secondary xylem Sapwood Figure 35.22 Growth ring Vascular ray Heartwood Secondary xylem Sapwood Figure 35.22 Anatomy of a tree trunk. Vascular cambium Secondary phloem Bark Layers of periderm

Figure 35.23 Figure 35.23 Is this tree living or dead?