Chapter23 Roots, Stems and Leaves Photo Credit: Getty Images Page 578.

Chapter23 Roots, Stems and Leaves Photo Credit: Getty Images Page 578

23–1 Specialized Tissues in Plants
Photo Credit: Getty Images

23-1 Introduction to Plants
Seed Plant Structure The three principal organs of seed plants are roots, stems, and leaves. These organs perform functions such as the transport of nutrients, protection, and coordination of plant activities.

absorb water and dissolved nutrients.
23-1 Introduction to Plants Seed Plant Structure Roots: absorb water and dissolved nutrients. anchor plants in the ground. protect the plant from harmful soil bacteria and fungi.

a support system for the plant body.
23-1 Introduction to Plants Seed Plant Structure Stems: a support system for the plant body. a transport system that carries nutrients. a defense system that protects the plant against predators and disease.

are a plant’s main photosynthetic systems.
23-1 Introduction to Plants Seed Plant Structure Leaves: are a plant’s main photosynthetic systems. increase the amount of sunlight plants absorb. Adjustable pores conserve water and let oxygen and carbon dioxide enter leave.

vascular tissue - transport ground tissue - structure
Plants consist of three main tissue systems: dermal tissue - outer vascular tissue - transport ground tissue - structure Plant Tissue Systems 23-1 Introduction to Plants

Seed Plant Structure 23-1 Introduction to Plants Leaf Stem
Vascular plants consist of roots, stems, and leaves. Each of these organs contains dermal tissue, vascular tissue, and ground tissue. Root

Dermal Tissue Dermal tissue is the outer covering of a plant and consists of epidermal cells. Epidermal cells make up dermal tissue. Epidermal cells are covered with a thick waxy layer, called the cuticle, which protects the plant against water loss and injury.

Dermal Tissue Some epidermal cells have projections called trichomes, that help protect the leaf and also give it a fuzzy appearance. In roots, dermal tissue includes root hair cells that provide a large amount of surface area and aid in water absorption. On the underside of leaves, dermal tissue contains guard cells, which regulate water loss and gas exchange.

Xylem consists of tracheids and vessel elements.
Vascular Tissue Vascular tissue forms a transport system that contains several types of specialized cells. Xylem consists of tracheids and vessel elements. Phloem consists of sieve tube elements and companion cells. 23-1 Introduction to Plants

Vascular Tissue 23-1 Introduction to Plants Cross Section of a Stem
Tracheid Companion cell Vascular tissue is made up of xylem and phloem. Xylem tissue conducts water from the roots to the rest of the plant. Phloem tissue conducts a variety of materials, mostly carbohydrates, throughout a plant. Photo Credit: Ray F. Evert, University of Wisconsin Vessel element Sieve tube element Xylem Phloem

All seed plants have tracheids.
23-1 Introduction to Plants Vascular Tissue Xylem All seed plants have tracheids. Tracheids are long, narrow cells that are impermeable to water, but they have holes that connect cells. Tracheid Vessel element Vascular tissue is made up of xylem and phloem. Xylem tissue conducts water from the roots to the rest of the plant.

Angiosperms also have vessel elements.
23-1 Introduction to Plants Vascular Tissue Angiosperms also have vessel elements. Vessel elements form a continuous tube through which water can move. Tracheid Vessel element Vascular tissue is made up of xylem and phloem. Xylem tissue conducts water from the roots to the rest of the plant.

Phloem contains sieve tube elements and companion cells.
23-1 Introduction to Plants Vascular Tissue Phloem Phloem contains sieve tube elements and companion cells. Sieve tube elements are phloem cells joined end-to-end to form sieve tubes. Companion cell Sieve tube element Vascular tissue is made up of xylem and phloem. Phloem tissue conducts a variety of materials, mostly carbohydrates, throughout a plant.

Vascular Tissue The end walls of sieve tube elements have many small holes that sugars and other foods can move through. Companion cell Sieve tube element Vascular tissue is made up of xylem and phloem. Phloem tissue conducts a variety of materials, mostly carbohydrates, throughout a plant.

Companion cells are phloem cells that surround sieve tube elements.
23-1 Introduction to Plants Vascular Tissue Companion cells are phloem cells that surround sieve tube elements. Companion cells support sieve tubes and aid in the movement of substances in and out of the phloem. Companion cell Sieve tube element Vascular tissue is made up of xylem and phloem. Phloem tissue conducts a variety of materials, mostly carbohydrates, throughout a plant.

Between dermal and vascular tissues are ground tissues.
Three kinds of ground tissue: Parenchyma- thin walls and large central vacuoles - storage Collenchyma- strong, flexible cell walls that help support larger plants Sclerenchyma- extremely thick, rigid cell walls = tough and strong 23-1 Introduction to Plants Ground Tissue

Ground Tissue

Growth & Meristematic Tissue
23-1 Introduction to Plants Growth & Meristematic Tissue In most plants, new cells are produced at the tips of the roots and stems. These cells are produced in meristems. Meristematic tissue is the only plant tissue that produces new cells by mitosis. A meristem is a cluster of tissue that is responsible for continuing growth throughout a plant's lifetime.

Growth & Meristematic Tissue
23-1 Introduction to Plants Growth & Meristematic Tissue Near the tip of each growing stem and root is an apical meristem. An apical meristem is at the tip of a growing stem or root.

23–2 Roots

23-2 Roots In some plants, the primary root grows long and thick and is called a taproot. Fibrous roots branch to such an extent that no single root grows larger than the rest. Types of Roots

23-2 Roots Types of Roots Plants have taproots, fibrous roots, or both. Taproots have a central primary root and generally grow deep into the soil. Fibrous roots are usually shallow and consist of many thin roots. Fibrous Roots Tap Roots

A carrot is an example of a taproot.
23-2 Roots Types of Roots A carrot is an example of a taproot. Plants have taproots, fibrous roots, or both. Taproots have a central primary root and generally grow deep into the soil. Fibrous roots are usually shallow and consist of many thin roots. Fibrous Roots Tap Roots

Fibrous roots are found in grasses.
Types of Roots Fibrous roots are found in grasses. Plants have taproots, fibrous roots, or both. Taproots have a central primary root and generally grow deep into the soil. Fibrous roots are usually shallow and consist of many thin roots. Fibrous Roots Tap Roots

Root Structure and Growth
Roots contain cells from dermal, vascular, and ground tissue.

A mature root has an outside layer, the epidermis, and a central cylinder of vascular tissue. Between these two tissues lies a large area of ground tissue. The root system plays a key role in water and mineral transport.

The root’s surface is covered with cellular projections called root hairs. Root hairs provide a large surface area through which water can enter the plant. Root hairs A root consists of a central vascular cylinder surrounded by ground tissue and the epidermis. Root hairs along the surface of the root aid in water absorption.

Epidermis The epidermis (including root hairs) protects the root and absorbs water.

Inside the epidermis is a layer of ground tissue called the cortex. Ground tissue (cortex) A root consists of a central vascular cylinder surrounded by ground tissue and the epidermis.

The cortex extends to another layer of cells, the endodermis. The endodermis completely encloses the vascular cylinder. Endodermis

The vascular cylinder is the central region of a root that includes the xylem and phloem. Phloem Vascular cylinder Xylem

Roots grow in length as their apical meristem produces new cells near the root tip. Apical meristem

These new cells are covered by the root cap that protects the root as it forces its way through the soil. Only the cells in the root tip divide. In the area just behind the root tip, the newly divided cells increase in length, pushing the root tip farther into the soil. The root cap, located just ahead of the root tip, protects the dividing cells as they are pushed forward. Apical meristem Root cap

nitrogen phosphorus potassium magnesium calcium Root Functions
23-2 Roots Root Functions The most important nutrients plants need include: nitrogen phosphorus potassium magnesium calcium

Active Transport of Minerals
23-2 Roots Root Functions Active Transport of Minerals The cell membranes of root epidermal cells contain active transport proteins.

23-2 Roots Root Functions Transport proteins use ATP to pump mineral ions from the soil into the plant. Root hairs Roots absorb water and dissolved nutrients from the soil. Most water and minerals enter a plant through the tiny root hairs.

23-2 Roots Root Functions The high concentration of mineral ions in the plant cells causes water molecules to move into the plant by osmosis. Roots absorb water and dissolved nutrients from the soil. Most water and minerals enter a plant through the tiny root hairs. Water moves into the cortex, through the cells of the endodermis, and into the vascular cylinder. Finally, water reaches the xylem, where it is transported throughout the plant.

Movement Into the Vascular Cylinder
23-2 Roots Root Functions Movement Into the Vascular Cylinder Osmosis and active transport move water and minerals from the root epidermis into the cortex. The water and dissolved minerals pass the inner boundary of the cortex and enter the endodermis.

Water moves into the vascular cylinder by osmosis.
23-2 Roots Root Functions The endodermis is composed of many individual cells. Water moves into the vascular cylinder by osmosis. Endodermis Cells in the endodermis are made waterproof by the Casparian strip. The Casparian strip prevents the backflow of water out of the vascular cylinder into the root cortex.

23-2 Roots Root Functions Each cell is surrounded on four sides by a waterproof strip called a Casparian strip. The Casparian strip prevents the backflow of water out of the vascular cylinder into the root cortex. Casparian strip Casparian strip

23-2 Roots Root Functions As more water moves from the cortex into the vascular cylinder, more water in the xylem is forced upward through the root into the stem. Root pressure pushes water through the vascular system of the entire plant.

23–3 Stems Photo Credit: Getty Images

Stem Structure and Function
Stem functions: they produce leaves, branches and flowers they hold leaves up to the sunlight they transport substances between roots and leaves Can do photosynthesis 23-3 Stems Stem Structure and Function

Stems make up an essential part of the water and mineral transport systems of the plant. Xylem and phloem form continuous tubes from the roots through the stems to the leaves. This allows water and nutrients to be carried throughout the plant.

Stems are surrounded by a layer of epidermal cells that have thick cell walls and a waxy protective coating.

Leaves attach to the stem at structures called nodes. The regions of stem between the nodes are internodes. Small buds are found where leaves attach to nodes. Bud Node Internode Node Stems produce leaves and branches and hold leaves up to the sunlight, where they carry out photosynthesis. Leaves are attached to a stem at structures called nodes. These nodes are separated by regions of the stem called internodes.

Buds contain undeveloped tissue that can produce new stems and leaves. In larger plants, stems develop woody tissue that helps support leaves and flowers. Bud

Monocot and Dicot Stems
Monocot Stems Monocot stems have a distinct epidermis, which encloses vascular bundles. Each vascular bundle contains xylem and phloem tissue. Epidermis Vascular bundles Ground tissue In a monocot, vascular bundles are scattered throughout the stem. Photo Credit: ©Ed Reschke/Peter Arnold, Inc. Monocot

Monocot Stems Vascular bundles are scattered throughout the ground tissue. Ground tissue consists mainly of parenchyma cells. Epidermis Vascular bundles Ground tissue In a monocot, vascular bundles are scattered throughout the stem. Photo Credit: ©Ed Reschke/Peter Arnold, Inc. Monocot

Dicot stems have vascular bundles arranged in a ringlike pattern. The parenchyma cells inside the vascular tissue are known as pith. Vascular bundles Epidermis In a dicot, vascular bundles are arranged in a ring. Photo Credit: ©Ed Reschke/Peter Arnold, Inc. Cortex Pith Dicot

The parenchyma cells outside of the vascular tissue form the cortex of the stem. Vascular bundles Epidermis Photo Credit: ©Ed Reschke/Peter Arnold, Inc. Cortex Pith Dicot

Primary Growth of Stems
All seed plants undergo primary growth, which is an increase in length. For the entire life of the plant, new cells are produced at the tips of roots and shoots. 23-3 Stems Primary Growth of Stems Primary growth Apical meristem Primary growth All seed plants undergo primary growth, which is an increase in length. Every year, apical meristems, shown in red, divide to produce new growth. The primary growth for one season consists of a stem and several leaves. Leaf scar Year 1 Year 2 Year 3

Primary Growth of Stems
Primary growth of stems is produced by cell divisions in the apical meristem. It takes place in all seed plants. 23-3 Stems Primary Growth of Stems Apical meristem All seed plants undergo primary growth, which is an increase in length. Every year, apical meristems, shown in red, divide to produce new growth. The primary growth for one season consists of a stem and several leaves.

Secondary Growth of Stems
Stems increase in width due to secondary growth. Secondary growth produces wood. Thin tree ring = slow growth, often due to drought.

Formation of the Vascular Cambium Once secondary growth begins, the vascular cambium appears as a thin layer between the xylem and phloem of each vascular bundle. Vascular cambium

The vascular cambium divides to produce xylem cells toward the center of the stem and phloem cells toward the outside. Secondary phloem Secondary xylem

Bark Wood Formation of Wood Wood is actually layers of xylem. These cells build up year after year. In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

As woody stems grow thicker, older xylem cells near the center of the stem no longer conduct water. This is called heartwood. Heartwood supports the tree. Xylem: Heartwood In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

Heartwood is surrounded by sapwood. Sapwood is active in water and mineral transport. Xylem: Sapwood In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

Formation of Bark On most trees, bark includes all of the tissues outside the vascular cambium — phloem, the cork cambium and cork. Bark In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

The vascular cambium produces new xylem and phloem, which increase the width of the stem. Vascular cambium In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

Phloem The phloem transports sugars produced by photosynthesis. In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside.

Cork cambium The cork cambium produces a protective layer of cork. In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

Cork The cork contains old, nonfunctioning phloem that protects the tree. In a mature tree that has undergone several years of secondary growth, the vascular cambium lies between layers of xylem to the inside, and layers of phloem to the outside. The youngest xylem, called sapwood, transports water and minerals.

23–4 Leaves Photo Credit: Getty Images

23-4 Leaves Leaf Structure The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

23-4 Leaves Leaf Structure To collect sunlight, most leaves have thin, flattened sections called blades. Blade Most of a leaf consists of a blade attached to the stem by a petiole. The blade of a simple leaf (left) can be different shapes. In a compound leaf (right), the blade is divided into many separate leaflets. Simple leaf Leaflet Petiole Bud Compound leaf Stem

The blade is attached to the stem by a thin stalk called a petiole.
23-4 Leaves Leaf Structure The blade is attached to the stem by a thin stalk called a petiole. Blade Most of a leaf consists of a blade attached to the stem by a petiole. The blade of a simple leaf (left) can be different shapes. In a compound leaf (right), the blade is divided into many separate leaflets. Simple leaf Leaflet Petiole Bud Compound leaf Stem

Simple leaves have only one blade and one petiole.
Leaf Structure Simple leaves have only one blade and one petiole. Blade Most of a leaf consists of a blade attached to the stem by a petiole. The blade of a simple leaf (left) can be different shapes. In a compound leaf (right), the blade is divided into many separate leaflets. Simple leaf Leaflet Petiole Bud Compound leaf Stem

23-4 Leaves Leaf Structure Compound leaves have several blades, or leaflets, that are joined together and to the stem by several petioles. Blade Most of a leaf consists of a blade attached to the stem by a petiole. The blade of a simple leaf (left) can be different shapes. In a compound leaf (right), the blade is divided into many separate leaflets. Simple leaf Leaflet Petiole Bud Compound leaf Stem

Leaves are covered on the top and bottom by epidermis.
Leaf Structure Leaves are covered on the top and bottom by epidermis. Epidermis Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates. Epidermis

The epidermis of many leaves is covered by the cuticle.
Leaf Structure The epidermis of many leaves is covered by the cuticle. Cuticle Epidermis Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates. Epidermis

23-4 Leaves Leaf Structure The cuticle and epidermal cells form a waterproof barrier that protects tissues inside the leaf and limits the loss of water through evaporation. The veins of leaves are connected directly to the vascular tissues of stems.

23-4 Leaves Leaf Structure In leaves, xylem and phloem tissues are gathered together into bundles that run from the stem into the petiole. In the leaf blade, the vascular bundles are surrounded by parenchyma and sclerenchyma cells.

All these tissues form the veins of a leaf.
23-4 Leaves Leaf Structure All these tissues form the veins of a leaf. Xylem Vein Phloem

Most leaves consist of a specialized ground tissue known as mesophyll.
Leaf Functions Palisade mesophyll Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates. Spongy mesophyll

23-4 Leaves Leaf Functions The layer of mesophyll cells found directly under the epidermis is called the palisade mesophyll. These closely-packed cells absorb light that enters the leaf. Palisade mesophyll Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates.

23-4 Leaves Leaf Functions Beneath the palisade mesophyll is the spongy mesophyll, a loose tissue with many air spaces between its cells. Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates. Spongy mesophyll

The air spaces connect with the exterior through stomata.
23-4 Leaves Leaf Functions The air spaces connect with the exterior through stomata. Stomata are openings in the underside of the leaf that allow carbon dioxide and oxygen to diffuse in and out. Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates. Stoma

23-4 Leaves Leaf Functions Each stoma consists of two guard cells that control the opening and closing of stomata by responding to changes in water pressure. Leaves absorb light and carry out most of the photosynthesis in a plant. Some of the most important manufacturing sites on Earth are found in the leaves of plants. The cells in plant leaves are able to use light energy to make carbohydrates. Guard cells

Transpiration is the loss of water through leaves.
Leaf Functions Transpiration is the loss of water through leaves. Transpiration pulls water from the roots through the vascular tissues and out the leaves.

Stoma are open in daytime, when photo -synthesis is active.
23-4 Leaves Leaf Functions When water pressure within guard cells is high, the stoma open. Stoma are open in daytime, when photo -synthesis is active. Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis. A stoma opens or closes in response to the changes in pressure within the guard cells that surround the opening. When the guard cells are swollen with water the stoma is open.

Stomata are closed at night, to prevent water loss.
23-4 Leaves Leaf Functions When water pressure within guard cells decreases, the stoma closes. Stomata are closed at night, to prevent water loss. Plants regulate the opening and closing of their stomata to balance water loss with rates of photosynthesis. A stoma opens or closes in response to the changes in pressure within the guard cells that surround the opening.

23–5 Transport in Plants

23-5 Transport in Plants Water Pressure Xylem tissue forms a continuous set of tubes that runs from the roots through stems and out into the spongy mesophyll of leaves. Active transport and root pressure cause water to move from soil into plant roots. Capillary action and transpiration also are needed to transport water and minerals.

Water Pressure The combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue of even the tallest plant. 23-5 Transport in Plants

Cohesion is the attraction of water molecules to each other.
23-5 Transport in Plants Water Pressure Cohesion is the attraction of water molecules to each other. Adhesion is the attraction between unlike molecules.

23-5 Transport in Plants Water Pressure The tendency of water to rise in a thin tube is called capillary action. Water is attracted to the walls of the tube, and water molecules are attracted to one another. Capillary action—the result of water molecules’ ability to stick to one another and to the walls of a tube—contributes to the movement of water up the cells of xylem tissue. As shown here, capillary action causes water to move much higher in a narrow tube than in a wide tube. Applying Concepts Which force—adhesion or cohesion—causes the water to stick to the walls of the glass tube?

23-5 Transport in Plants Water Pressure Capillary action causes water to move much higher in a narrow tube than in a wide tube. Capillary action—the result of water molecules’ ability to stick to one another and to the walls of a tube—contributes to the movement of water up the cells of xylem tissue. As shown here, capillary action causes water to move much higher in a narrow tube than in a wide tube. Applying Concepts Which force—adhesion or cohesion—causes the water to stick to the walls of the glass tube?

Tracheids and vessel elements form hollow connected tubes in a plant.
23-5 Transport in Plants Water Pressure Tracheids and vessel elements form hollow connected tubes in a plant. Capillary action in xylem causes water to rise well above the level of the ground.

When water is lost through transpiration, osmotic pressure moves water out of the vascular tissue of the leaf. 23-5 Transport in Plants Water Pressure Root pressure, capillary action, and transpiration contribute to the movement of water within a plant. Transpiration is the movement of water molecules out of leaves. The faster water evaporates from a plant, shown in A, the stronger the pull of water upward from the roots, shown in B.

This process is known as transpirational pull.
23-5 Transport in Plants Water Pressure The movement of water out of the leaf “pulls” water upward through the vascular system all the way from the roots. This process is known as transpirational pull. Root pressure, capillary action, and transpiration contribute to the movement of water within a plant. Transpiration is the movement of water molecules out of leaves. The faster water evaporates from a plant, shown in A, the stronger the pull of water upward from the roots, shown in B.

Controlling Transpiration
23-5 Transport in Plants Water Pressure Controlling Transpiration The water content of the leaf is kept relatively constant. When there is a lot of water, water pressure in the guard cells is increased and the stomata open. Excess water is lost through open stomata by transpiration.

Many plants pump sugars into their fruits.
23-5 Transport in Plants Nutrient Transport Many plants pump sugars into their fruits. In cold climates, plants pump food into their roots for winter storage. This stored food must be moved back into the trunk and branches of the plant before growth begins again in the spring.

Movement from Source to Sink
23-5 Transport in Plants Nutrient Transport Movement from Source to Sink A process of phloem transport moves sugars through a plant from a source to a sink. A source is any cell in which sugars are produced by photosynthesis. A sink is any cell where the sugars are used or stored.

23-5 Transport in Plants Nutrient Transport The pressure-flow hypothesis explains how phloem transport takes place.

Pressure-Flow Hypothesis
23-5 Transport in Plants Nutrient Transport Pressure-Flow Hypothesis Phloem Xylem Sugar molecules Sugars produced during photosynthesis are pumped into the phloem (source). Source cell The diagram shows the movement of sugars and water throughout the phloem and xylem as explained by the pressure-flow hypothesis. Materials move from a source cell, where photosynthesis produces a high concentration of sugars, to a sink cell, where sugars are lower in concentration. Movement of water Movement of sugar

23-5 Transport in Plants Nutrient Transport Phloem Xylem Pressure-Flow Hypothesis Sugar molecules As sugar concentrations increase in the phloem, water from the xylem moves in by osmosis. Source cell The diagram shows the movement of sugars and water throughout the phloem and xylem as explained by the pressure-flow hypothesis. Materials move from a source cell, where photosynthesis produces a high concentration of sugars, to a sink cell, where sugars are lower in concentration. Movement of water Movement of sugar

23-5 Transport in Plants Nutrient Transport Pressure-Flow Hypothesis Phloem Xylem Sugar molecules This movement causes an increase in pressure at that point, forcing nutrient-rich fluid to move through the phloem from nutrient- producing regions …. Source cell The diagram shows the movement of sugars and water throughout the phloem and xylem as explained by the pressure-flow hypothesis. Materials move from a source cell, where photosynthesis produces a high concentration of sugars, to a sink cell, where sugars are lower in concentration. Movement of water Movement of sugar

…. toward a region that uses these nutrients (sink).
23-5 Transport in Plants Nutrient Transport Pressure-Flow Hypothesis Movement of water …. toward a region that uses these nutrients (sink). Movement of sugar The diagram shows the movement of sugars and water throughout the phloem and xylem as explained by the pressure-flow hypothesis. Materials move from a source cell, where photosynthesis produces a high concentration of sugars, to a sink cell, where sugars are lower in concentration. Sink cell Phloem Xylem

23-5 Transport in Plants Nutrient Transport Pressure-Flow Hypothesis Movement of water If part of a plant actively absorbs nutrients from the phloem, osmosis causes water to follow. Movement of sugar This decreases pressure and causes a movement of fluid in the phloem toward the sink. The diagram shows the movement of sugars and water throughout the phloem and xylem as explained by the pressure-flow hypothesis. Materials move from a source cell, where photosynthesis produces a high concentration of sugars, to a sink cell, where sugars are lower in concentration. Sink cell Phloem Xylem

Chapter23 Roots, Stems and Leaves Photo Credit: Getty Images Page 578.

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