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Chapter 17 Plant Form and Function Lectures by Gregory Ahearn University of North Florida Copyright © 2009 Pearson Education, Inc.. 17.1 How Are Plant Bodies Organized? Flowering plants have a root system and a shoot system. • Flowering plant bodies consist of two major parts: the root system and the shoot system. • Roots are branched portions of the plant body that are usually embedded in soil and serve to anchor the plant and absorb water and nutrients from the soil. Copyright © 2009 Pearson Education Inc. 17.1 How Are Plant Bodies Organized? Flowering plants have a root system and a shoot system (continued). • The part of the plant above ground is the shoot system, and consists of leaves, buds, flowers, and fruit born on stems. • The functions of shoots include photosynthesis, reproduction, and transport between different parts of the plant body. Copyright © 2009 Pearson Education Inc. apical meristem beginning leaves terminal bud flower stem leaf lateral bud Shoot system branch tap root Root system branch roots root hairs root cap Fig. 17-1 Copyright © 2009 Pearson Education Inc. 17.1 How Are Plant Bodies Organized? Flowering plants can be divided into two groups: • The monocots, which include the grasses, lilies, palms, and orchids • The dicots, which include deciduous trees (those that drop their leaves in winter), bushes, and many garden flowers Copyright © 2009 Pearson Education Inc. 17.1 How Are Plant Bodies Organized? Leaves Stems Roots Monocots Flowers Seeds embryo cotyledon Flower parts are in threes or multiples of three Leaves have smooth edges, often narrow, with parallel veins Vascular bundles are scattered throughout the stem Monocots have a fibrous root system The seed has one cotyledon (seed leaf) Dicots embryo Flower parts are in fours or fives or multiples of four or five cotyledons Leaves are palmate (handlike) or oval with netlike veins Vascular bundles are arranged in a ring around the stem Dicots have a taproot system The seed has two cotyledons (seed leaves) Fig. 17-2 Copyright © 2009 Pearson Education Inc. 17.2 How Do Plants Grow? During growth, meristem cells give rise to differentiated cells. • Plant bodies are composites of two fundamentally different kinds of cells: meristem and differentiated cells. • Meristem cells are capable of mitosis. • Some meristem cells stop dividing and become permanent, non-mitotic differentiated cells. • Differentiated cells become mature leaves or trunks of trees. Copyright © 2009 Pearson Education Inc. 17.2 How Do Plants Grow? During growth, meristem cells give rise to differentiated cells (continued). • Plants grow by cell division of two types of meristem cells: • Apical meristem, at tips of roots and shoots • Lateral meristem, also called cambia, form cylinders that run lengthwise inside roots and stems Copyright © 2009 Pearson Education Inc. 17.2 How Do Plants Grow? Different processes are responsible for growth in length and width. • Primary growth occurs by division of apical meristem cells, and leads to growth in length at the tips of roots and shoots. • Secondary growth occurs by mitotic division of lateral meristem cells, and increases the thickness of the stems and roots as they age. Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? The structures of plants consist of three types of plant tissues: • Dermal tissue, which covers the outer surfaces of the plant body • Ground, nondermal, nonvascular tissue that makes up most of the body of young plants • Vascular tissue, which transports water, nutrients, and sugars throughout the plant Copyright © 2009 Pearson Education Inc. ground tissue dermal tissue system vascular tissue system ground tissue system vascular tissue system Root system vascular tissue Shoot system 17.3 What Are The Tissues And Cell Types Of Plants? The structure of the root and shoot Fig. 17-3 Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Dermal tissue covers the plant body. • The outermost covering on leaves, stems, and roots of all young plants is part of the dermis called the epidermis. • This part of the plant is covered by a waterproof layer known as a cuticle, which reduces evaporation of water from the plant. • Roots have no cuticle because it would prevent the absorption of water and nutrients from the soil. • Epidermal cells are replaced by cork cells as the plant ages. Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Dermal tissues cover plant surfaces. stomata leaf hair Fig. 17-4 Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Ground tissue makes up most of the young plant body. • Ground tissue cells typically carry out most of the metabolic activities of the plant. • These tissues may photosynthesize, store sugars and starches, or secrete hormones. • Roots of plants, like carrots and sweet potatoes, are packed with ground tissue that stores carbohydrates such as starch and sugar. • Ground tissue also provides support in stems such as celery stalks. Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Vascular tissue consists of xylem and phloem. • Vascular tissue occurs in strands, called vascular bundles, that contain both xylem and phloem. Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Xylem conducts water and dissolved nutrients from the roots to the rest of the plant. • Xylem tissues are called tracheids and vessel elements. • Tracheids are thin in diameter, while the vessel elements are wider and provide a relatively unobstructed pipeline from root to leaf. Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Xylem ground tissue cells (fibers) pits Pits link the insides of the tracheids and vessel elements Openings connect the vessel elements end wall tracheids vessel element (a) Xylem structure tracheids vessel element (b) Longitudinal section of xylem Fig. 17-5 Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Phloem conducts substances throughout the plant. • Substances that are synthesized by the plant—such as sugars, amino acids, and hormones—are conducted through the plant by phloem. • Phloem has sieve tubes that form continuous conducting tubes that connect all parts of the plant. Copyright © 2009 Pearson Education Inc. 17.3 What Are The Tissues And Cell Types Of Plants? Phloem ground tissue cells Sieve plates connect the sieve-tube elements sieve plate with pores sieve-tube element companion cell nucleus (a) Phloem structure Copyright © 2009 Pearson Education Inc. companion cell (b) Cross section of phloem Fig. 17-6 17.4 How Do Roots Grow And What Do They Do? Dicots and monocots have different types of roots. • Dicots, such as carrots and dandelions, have a single taproot with smaller side roots. • Monocots, like grasses and palms, have numerous roots at the base of the plant that are the same size, called fibrous roots. Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? Taproots and fibrous roots Fig. 17-7 Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? Roots elongate by primary growth. • In young roots, divisions of the apical meristem give rise to four distinct regions: • An outer envelop of epidermis • A vascular cylinder at the core of the root • A cortex between the two • A protective root cap at the tip of the root that protects the apical meristem from being scraped off as the root pushes downward Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? epidermis root hair cortex endodermis of cortex xylem phloem vascular cylinder apical meristem root cap Fig. 17-8 Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? The epidermis of the root is very permeable to water. • The root’s outermost covering of cells is the epidermis, which contacts the soil and any air or water trapped among the soil particles. • The cell walls of epidermal cells are highly water permeable, allowing water to penetrate into the interior of the root. Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? Many epidermal cells have root hairs, which are long, thin extensions that grow into the surrounding soil and increase the roots ability to root hairs absorb water and nutrients. Fig. 17-9 Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? The cortex controls the absorption of water and nutrients. • Cortex is a type of ground tissue that makes up most of the inside of a young root. • The cortex consists of an outer mass of large, loosely packed cells just beneath the epidermis, and an inner layer of smaller, close-fitting cells called the endodermis, which encircles the vascular cylinder. Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? The cortex controls the absorption of water and nutrients (continued). • Water and nutrients move from the cortex into the vascular cylinder by moving across the membranes of the endodermal cells, which regulate the types and amounts of materials that the roots absorb. Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? The vascular cylinder contains xylem and phloem, and meristem for branch roots. • The vascular cylinder of a root contains the conducting tissues of xylem and phloem, which transport water and dissolved materials within the plant. • The outermost layer of the vascular cylinder retains the ability to divide and form the apical meristem of new roots that grow as branches from existing roots. Copyright © 2009 Pearson Education Inc. 17.4 How Do Roots Grow And What Do They Do? A new branch root breaks out through the cortex and epidermis of the primary root by secreting enzymes that digest them away. The vascular tissues of the branch root connect with the vascular tissues of the primary root. Fig. 17-10 Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Stems grow in length by the mitotic apical stem cells of the terminal bud. • The apical meristem differentiates into four specialized cell types: stem cells, bud cells, leaf cells, and flower cells. • Young stems are composed of four tissues: • Epidermis (dermal tissue) • Cortex (ground tissue) • Pith (ground tissue) • Vascular tissue Copyright © 2009 Pearson Education Inc. terminal bud beginning leaves apical meristem sunflower (dicot) stem pith node lateral bud epidermis internode blade stalk branch (sprouted lateral bud) vascular cortex bundle leaf pith epidermis pith vascular bundle Copyright © 2009 Pearson Education Inc. cortex phloem vascular cambium xylem phloem vascular cambium xylem stem vascular bundle Fig. 17-11 17.5 How Do Stems Grow And What Do They Do? The epidermis of the stem retards water loss while allowing carbon dioxide to enter. • The epidermis is perforated with adjustable pores called stomata (singular, stoma) that permit and regulate the movement of carbon dioxide and oxygen. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? The cortex and pith support the stem, store food, and photosynthesize. • There are two types of ground tissue in stems: • Cortex • Pith • These ground tissues perform three major functions—support, storage, and photosynthesis. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Vascular tissues in stems transport water, dissolved nutrients, and hormones. • Xylem and phloem of stems transport water, nutrients, sugars, and hormones. • Vascular tissues are continuous in the root, stem, and leaf, interconnecting all parts of the plant. • Xylem and phloem in young stems arise from the apical meristem, and are called primary xylem and primary phloem. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Branches form from lateral buds consisting of meristem cells. • As the shoot grows, small clusters of meristem cells are left behind on the surface of the stem. • Some of these meristem cells form leaves, and others form lateral buds that grow into branches. • Lateral buds are located just above the attachment points of leaves. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? A bud sprouts from these meristem cells when stimulated by a hormone, and this becomes a branch that has its own apical meristem and makes its own leaves. Fig. 17-12 Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Secondary growth produces thicker, stronger stems. • Secondary growth results from cell division in two lateral meristems: • The vascular meristem • The cork cambium Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Vascular cambium produces secondary xylem and phloem. • The vascular cambium is a cylinder of meristem cells located between the primary xylem and the primary phloem. • Daughter cells of the vascular cambium produced toward the inside of the stem differentiate into secondary xylem, and those produced toward the outside of the stem differentiate into secondary phloem. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Vascular cambium produces secondary xylem and phloem (continued). • Since the center of the stem already is filled with pith and primary xylem, newly formed secondary xylem pushes the vascular cambium farther out, increasing the diameter of the stem. Copyright © 2009 Pearson Education Inc. Secondary growth (a) Cross section of stem End of primary growth secondary phloem primary phloem vascular cambium primary xylem secondary xylem epidermis cork cambium cork pith cortex pith cortex primary xylem primary xylem dividing vascular cambium new secondary xylem dividing vascular cambium new secondary phloem primary phloem (b) Detail of vascular bundle primary phloem Fig. 17-13 Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Tree rings reflect seasonal changes. • Tree rings form from seasonal changes in vascular cambium growth. • In temperate climates, vascular cambium growth ceases in the winter but starts to grow in the spring, forming new xylem and phloem. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Tree rings reflect seasonal changes (continued). • In spring months, the new cells are large due to extensive water uptake, but in summer months, when water is more scarce, the cells are smaller. • As a result, cross-sections of tree trunks show a banding pattern of these different cells that form annual growth rings, which can be used to age the tree. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Secondary growth causes the epidermis to be replaced by woody cork. • Epidermal cells are mature, differentiated cells that can no longer divide. • Therefore, as new secondary xylem and phloem enlarge the stem, the epidermis splits and dies. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Secondary growth causes the epidermis to be replaced by woody cork (continued). • Then some cells of the cortex form a new lateral meristem—the cork cambium—which produces daughter cells toward the outside of the stem. • These daughter cells become cork cells that protect the tree from damage as they become part of the tree bark. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? PLAY Animation—Primary and Secondary Growth Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Some specialized stems produce new plants or store water or food. • Many plants have stems that are modified to perform functions very different from the original one of raising leaves up to the light. Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? Strawberries grow stems that snake out over the soil, sprouting new strawberry plants where lateral buds touch the soil. Fig. 17-14a Copyright © 2009 Pearson Education Inc. 17.5 How Do Stems Grow And What Do They Do? The Baobab tree stores water in aboveground stems; other plants, such as the potato, store carbohydrates in underground stems. Fig. 17-14b Copyright © 2009 Pearson Education Inc. 17.6 What Is The Structure Of Leaves And What Do They Do? Leaves are the major site of photosynthesis in plants. Photosynthesis produces sugars (glucose) and oxygen from water, CO2, and sunlight. Copyright © 2009 Pearson Education Inc. 17.6 What Is The Structure Of Leaves And What Do They Do? Leaves have two major parts: • The leaf epidermis consists of a layer of nonphotosynthetic, transparent cells that secrete a cuticle that reduces evaporation; adjustable pores called stomata surrounded by guard cells occur throughout the epidermis and regulate gas exchange. • Beneath the epidermis is the mesophyll, which contains the chloroplasts for photosynthesis. Copyright © 2009 Pearson Education Inc. 17.6 What Is The Structure Of Leaves And What Do They Do? A typical dicot leaf cuticle upper epidermis chloroplasts upper epidermis mesophyll lower epidermis cuticle xylem phloem (a) Leaf structure guard cell stoma stoma phloem lower epidermis (b) Leaf cross section xylem Fig. 17-15 Copyright © 2009 Pearson Education Inc. 17.6 What Is The Structure Of Leaves And What Do They Do? Specialized leaves may provide support, store food, or even capture insects. • In some plants, modified leaves serve functions unrelated to photosynthesis or water conservation. • The common edible pea grasps fences with clinging tendrils, which are slender, supple leaflets. • Some plants—like onions, daffodils, and tulips—use thick, fleshy leaves as foodstorage organs. Copyright © 2009 Pearson Education Inc. 17.6 What Is The Structure Of Leaves And What Do They Do? A few plants have become predators; sundews have leaves that are modified into snares for trapping insects. Fig. 17-16 Copyright © 2009 Pearson Education Inc. 17.7 How Do Plants Acquire Nutrients? Plants require a long list of important nutrients for normal life, which come from the soil or air. • • • • • Carbon dioxide Hydrogen and oxygen Phosphorus Nitrogen Minerals such as magnesium, calcium, and potassium • Micronutrients such as iron, copper, manganese, zinc, boron, and molybdenum Copyright © 2009 Pearson Education Inc. 17.7 How Do Plants Acquire Nutrients? Fungi and bacteria help plants acquire nutrients. • Root-fungus complexes are called mycorrhizae, and they help plants extract and absorb minerals from the soil. Fig. 17-17 Copyright © 2009 Pearson Education Inc. 17.7 How Do Plants Acquire Nutrients? Plants need a lot of nitrogen; much comes from the air, but some plants have symbiotic bacteria in root nodules that convert N2 gas into ammonium or nitrate, which the plants can then use. This process is called nitrogen-fixation. • Plants that have nitrogen-fixing bacteria are called legumes (e.g., peas, clover, and soybeans). Copyright © 2009 Pearson Education Inc. 17.7 How Do Plants Acquire Nutrients? Nitrogen fixation in legumes Fig. 17-18 Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? Nearly 99% of the water absorbed by the roots of plants evaporates through the stomata of leaves in a process called transpiration. • Transpiration drives the movement of water through the plant body by pulling water up through the xylem of the roots and stem into the leaves. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? Transpiration provides the force for water movement in xylem. • As the leaf transpires, the water concentration in its mesophyll drops, which causes water to move by osmosis from the leaf’s xylem into the mesophyll cells. • Because of hydrogen bonding between adjacent water molecules, when one water molecule leaves, it pulls other water molecules up the xylem from the stem and the roots. Copyright © 2009 Pearson Education Inc. Water evaporates through the stomata of leaves flow of water water molecules Cohesion of water molecules to one another and adhesion to the xylem wall by hydrogen bonds creates a “water chain” Water enters the vascular cylinder of the root Fig. 17-19 Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? Water enters roots mainly by pressure differences created by transpiration. • The upward movement of water ultimately causes soil water to move into the roots. • The main force powering the flow of water from the soil to the root’s vascular cylinder is low water pressure in the cylinder. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? Water enters roots mainly by pressure differences created by transpiration (continued). • This low pressure is due to the fact that water is always drawn away by moving upward through the xylem to replace water lost through transpiration from the leaves. • This force is strong enough that roots can absorb water, even from quite dry soils. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? Adjustable stomata control the rate of transpiration. • Transpiration is a plant’s largest source of water loss. • Most water is lost through the stomata in the leaves; because photosynthesis requires carbon dioxide from the air, the stomata have to be open to obtain this gas. • To meet these requirements, stomata are open during the day, when sunlight allows photosynthesis, and closed at night, conserving water. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? PLAY Animation—Plant Transport Mechanisms Copyright © 2009 Pearson Education Inc. Water Transport In Plants Suggested Media Enhancement: Water Transport in Plants To access this animation go to folder C_Animations_and_Video_Files and open the BioFlix folder. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? The pressure-flow theory explains sugar movement in phloem. • Sugars made by photosynthesis must be moved to other parts of the plant. • Sugars, dissolved in water to form sap, also contain amino acids and hormones, and travel throughout the phloem. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? The pressure-flow theory explains sugar movement in phloem (continued). • After reaching their destination, the sugars may nourish non-photosynthetic cells of roots or flowers, or may be stored for later use. • Sap is propelled through phloem by differences in water pressure created by the difference between the production and use of sugar in different parts of the plant. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? The pressure flow theory is illustrated in four steps. 1. The sugar produced by a source cell is moved by active transport into a phloem tube. 2. Water follows the sugar into the tube by osmosis. 3. The increased water pressure forces the sugar-rich sap through the phloem tubes into regions of lower pressure. 4. Cells of a sugar sink actively transport sugar out of the phloem, with water following by osmosis. Copyright © 2009 Pearson Education Inc. 17.8 How Do Plants Acquire Water And Transport Water And Nutrients? Pressure differences power the movement of sugars. xylem phloem sunlight sugar source sugar source cell sugar sink sugar sink cell Fig. 17-20 Copyright © 2009 Pearson Education Inc.