Chapter 35 Plant Structure Growth and Development Power

Chapter 35 Plant Structure, Growth, and Development Power. Point Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Overview of Plant Structure • BOTH genes and the environment affect plant structure and physiology. • Plants have THREE BASIC ORGANS: roots, stems, and leaves. • Plant organs are composed of THREE TISSUE SYSTEMS: dermal, vascular, and ground. • Parenchyma, collenchyma, and sclerenchyma are three TYPES OF PLANT CELLS • The move to land forced development of adaptations – natural selection. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Three Basic Plant Organs: Roots, Stems, and Leaves • The plant body has a hierarchy of organs, tissues, and cells • Plants, like multicellular animals – Have organs composed of different tissues, which are in turn composed of cells • The basic morphology of vascular plants – Reflects their evolutionary history as terrestrial organisms that draw nutrients from two very different environments: below-ground above-ground Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Forces of Nature • Why 2 different systems? – Soil – provides water and minerals, but no light present – Air – source of CO 2 • SO, plants developed 2 systems: – Root systems (subterranean) – Shoot systems (aerial) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Plant Organs: Roots, Stems, and Leaves • Plant organs are organized into a root system and a shoot system Reproductive shoot (flower) Terminal bud The root system and the shoot system are connected by vascular tissue (purple strands) that is continuous throughout the plant. Node Internode Terminal bud Shoot system Vegetative shoot Leaf Blade Petiole Axillary bud Stem Taproot Lateral roots Figure 35. 2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Root system

3 Organs of Plants • Roots – – *anchor plant, prevent erosion – *absorb minerals and water – *store food • Stems – – *transport system – *store food (tubers – ex potato) – *support leaves – *protect tissues • Leaves – *photosynthesis – *funnel water to roots Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Roots • A root – Is an organ that anchors the vascular plant – Absorbs minerals and water – Often stores organic nutrients • 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 Figure 35. 3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Root Types • Many plants have modified roots • Fibrous vs. Taproot – Fibrous: mat of thin roots that spread out below ground (monocots). – Taproot: consists of one large, vertical root (dicots). • Root Hairs – provide surface area for max absorption of H 2 O • Adventitious Roots – roots that arise above ground from stems or even from leaves…help support plant. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Root Structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Stems and Buds • 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 • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Stem (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. Node Root Figure 35. 5 a–d (b) Bulbs are vertical, underground shoots consisting (c) Tubers, such as these mostly of the enlarged bases red potatoes, are enlarged of leaves that store food. You ends of rhizomes specialized can see the many layers of for storing food. The “eyes” modified leaves attached arranged in a spiral pattern to the short stem by slicing an around a potato are clusters onion bulb lengthwise. of axillary buds that mark the nodes. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rhizome Root

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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Leaf Morphology and Classification of Angiosperms • In classifying angiosperms taxonomists may use leaf morphology as a criterion (a) Simple leaf. A simple leaf is a single, undivided blade. Some simple leaves are deeply lobed, as in an oak leaf. Petiole (b) Compound leaf. In a compound leaf, the blade consists of multiple leaflets. Notice that a leaflet has no axillary bud at its base. (c) Doubly compound leaf. In a doubly compound leaf, each leaflet is divided into smaller leaflets. Figure 35. 6 a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Axillary bud Leaflet Petiole Axillary bud

Modified Leaves • 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. Figure 35. 6 a–e (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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Three Tissue Systems: Dermal, Vascular, and Ground • Each plant organ has dermal, vascular, and ground tissues Vascular – transport (xylem and phloem) Dermal – outer coverings, protection, water conservation (epidermis, cuticle) Ground – filler, packing material for cushioning Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Tissue Systems in Plants • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Parenchyma, Collenchyma, and Sclerenchyma Cells Unspecialized plant cell that carries most of the metabolism, synthesizes and stores organic products, and develops into a more differientiated cell type. Flexible plant cell that occurs in strands or cylinders that support young plant parts of the plant without restraining growth. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rigid, supportive plant cell usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity.

Plant Meristems • Meristems generate cells for new organs • Apical meristems produce primary growth – Are located at the tips of roots and in the buds of shoots – Elongate shoots and roots through primary growth • Lateral meristems produce secondary growth – Add thickness to woody plants through secondary growth Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Figure. 35. 10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Secondary xylem Periderm Cork cambium The cork cambium adds secondary dermal tissue. Cortex Primary phloem The vascular cambium adds Secondary secondary phloem xylem and Vascular cambium phloem.

Growth in Woody Plants • Primary and secondary growth occur simultaneously but in different locations Terminal bud Bud scale Axillary buds Leaf scar Node This year’s growth (one year old) Stem Internode One-year-old side branch formed from axillary bud near shoot apex Leaf scar Last year’s growth (two years old) Figure 35. 11 Growth of two years ago (three years old) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Scars left by terminal bud scales of previous winters Leaf scar

Primary Growth • 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 • The primary growth of roots – Produces the epidermis, ground tissue, and vascular tissue Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Ground Zone of maturation Vascular Zone of elongation Apical meristem Root cap Figure 35. 12 100 m Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zone of cell division

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 Apical meristem Leaf primordia -bearing nodes Developing vascular strand Axillary bud meristems Figure. 35. 15 0. 25 mm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Secondary Plant Growth • Secondary growth adds girth to stems and roots in woody plants • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Primary and Secondary Growth of a Stem (a) Primary and secondary growth in a two-year-old stem Epidermis Cortex Primary phloem Vascular cambium Primary xylem Pith Periderm (mainly cork cambia and cork) 1 In the youngest part of the stem, you can see the primary plant body, as formed by the apical meristem during primary growth. The vascular cambium is beginning to develop. 1 2 As primary growth continues to elongate the stem, the portion of the stem formed earlier the same year has already started its secondary growth. This portion increases in girth as fusiform initials of the vascular cambium form secondary xylem to the inside and secondary phloem to the outside. Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis 2 Phloem ray th 3 Grow Xylem ray Primary xylem Secondary xylem Vascular cambium Secondary phloem Cork Primary phloem 4 First cork cambium th Grow 3 The ray initials of the vascular cambium give rise to the xylem and phloem rays. 4 As the diameter of the vascular cambium increases, the secondary phloem and other tissues external to the cambium cannot keep pace with the expansion because the cells no longer divide. As a result, these tissues, including the epidermis, rupture. A second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex. The cork cambium produces cork cells, which replace the epidermis. 5 In year 2 of secondary growth, the vascular cambium adds to the secondary xylem and phloem, and the cork cambium produces cork. 6 6 As the diameter of the stem continues to increase, the outermost tissues exterior to the cork cambium rupture and slough off from the stem. Primary phloem Secondary phloem Vascular cambium Secondary xylem Primary xylem Pith Figure 35. 18 a Secondary xylem (two years of production) Vascular cambium Secondary phloem 5 Most recent cork cambium Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 7 Cork cambium re-forms in progressively deeper layers of the cortex. When none of the original cortex is left, the cork cambium develops from parenchyma cells in the secondary phloem. 8 Each cork cambium and the tissues it produces form a layer of periderm. 9 Bark consists of all tissues exterior to the vascular cambium. 8 Layers of periderm 9 Bark 7 Cork

Anotomy of a Three Year Old Stem Secondary phloem Vascular cambium Cork Secondary Late wood Early wood xylem Periderm (b) Transverse section of a three-yearold stem (LM) Xylem ray Bark 0. 5 mm Figure 35. 18 b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 0. 5 mm

Anatomy of a Tree Trunk Growth ring Vascular ray Heartwood Secondary xylem Sapwood Vascular cambium Secondary phloem Bark Layers of periderm Figure 35. 20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Cork Cambia 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Growth: Cell Division and Cell Expansion • Growth, morphogenesis, and differentiation produce the plant body • The three developmental processes of growth, morphogenesis, and cellular differentiation act in concert to transform the fertilized egg into a plant • By increasing cell number – Cell division in meristems increases the potential for growth • Cell expansion – Accounts for the actual increase in plant size • The plane (direction) and symmetry of cell division – Are immensely important in determining plant form Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Leaf Anatomy • The epidermis is covered by a waxy cuticle made of cutin to minimize water loss. The cuticle is transparent to allow light to penetrate. • Guard cells are modified epidermal cells that contain chloroplasts, are photosynthetic, and control the opening of stomates. – Stomata are tiny pores flanked by guard cells – they allow gas exchange between the leaf and surrounding air. Guard cell behavior is controlled by turgor pressure. – Transpiration is the loss of water through the stomata of plants. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Leaf Anatomy • The inner part of the leaf consists of palisade parenchyma and spongy mesophyll cells whose function is photosynthesis. – The cells in the palisade layer are packed tightly, while the spongy cells are loosely packed to allow for diffusion of gases into and out of these cells. • Xylem transport water to leaf tissues. Phloem transports “food” from leaf tissues to sink cells. – In phloem, hydrostatic pressure is generated at one side of a sieve tube, forcing sap to the opposite end of the tube (a concept known as bulk flow). • Vascular bundles or veins are located in the mesophyll and carry water and nutrients from the soil to the leaves and also carry sugar from the leaves to the rest of the plant. • Specialized mesophyll cells called bundle sheath cells surround the veins and separate them from the rest of the mesophyll. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 Figure 35. 17 a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vein Air spaces Guard cells (c) Transverse section of a lilac 100 µm (Syringa) leaf (LM)

Leaf Adaptations to Various Environments • Many leaves have specialized adaptations to various environments: – small leaves found on conifers reduce water loss – succulents have leaves modified for storing water – cacti have spines – modified leaves that reduce water loss – C 4 and CAM plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings