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Plant Anatomy and Nutrient Transport

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1 Plant Anatomy and Nutrient Transport
Chapter 43

2 In order to survive, plants have to…
The best ways to appreciate plants is to consider how they overcome the challenges encountered by life on Earth Obtain energy Obtain water and other nutrients Distribute water and nutrients through the body Exchange gases Support the body Grow and develop Reproduce Evolution has produced a variety of different types of plants

3 Plant body Organization
Two major parts The root system of a plant The shoot system

4 Root Systems Branched portions of the plant body Embedded in the soil
Six functions - Anchor the plant Absorb water and minerals from soil Store surplus food, carbohydrates manufactured in the shoot Transport water, minerals, sugars, hormones to and from shoot Produce hormones Interact with soil fungi and bacteria that help provide nutrients to the plant

5 The Shoot The shoot system is buds, leaves, flowers, fruits - all on parts of stems Buds give rise to leaves or flowers Leaves - sites of photosynthesis Flowers - reproductive organs, producing male and female gametes, then help them to reach one another Flowers produce seeds enclosed within fruits (protect and aid in dispersal) Stems - branched, elevate the leaves, flowers, fruit Elevating the fruit helps disperse the seeds Some parts are specialized to transport water, minerals, food molecules, others produce hormones

6 Two groups of flowering plants
Monocots - lilies, daffodils, tulips, palm trees, grasses— lawn grasses, and wheat, rice, corn, oats, bamboo Dicots - “broad-leafed” plants, including deciduous trees, bushes, vegetables, and flowers in fields and gardens There are differences between monocots and dicots, but the characteristic that gives these groups their name is the number of cotyledons The part of a plant embryo that absorbs and stores food reserves in the seed, then transfers the food to the rest to the embryo when the seed sprouts Monocots have a single cotyledon Dicots have two cotyledons

7 The Structures and Functions of a Flowering Plant
growth and development of plant structures leaf primordia apical meristem terminal bud lateral bud reproduction node flower body support; transport of water and nutrients stem fruit shoot system reproduction blade leaf energy acquisition by photosynthesis; gas exchange petiole branch root root system Acquisition of water and minerals branch roots root hairs root cap

8 Characteristics of Monocots and Dicots
Flowers Leaves Stems Roots Seeds embryo Monocots cotyledon Flower parts are in threes or multiples of three Vascular bundles are scattered throughout the stem Leaves have smooth edges, often narrow, with parallel veins Monocots have a fibrous root system The seed has one cotyledon (seed leaf) embryo Dicots cotyledons Flower parts are in fours or fives or multiples of four or five Vascular bundles are arranged in a ring around the stem The seed has two cotyledons (seed leaves) Leaves are palmate (handlike) or oval with netlike veins Dicots have a taproot system

9 Plant Development Dramatically different from animals
One difference - timing and distribution of growth In animals, the proportions of a newborn differs from an adult, parts of a newborn’s body grow until they reach adult size and structure, then growth stops Flowering plants grow throughout their lives, never reaching a stable adult body form Most plants grow longer or taller only at the tips of their branches and roots A swing tied to a tree branch or initials carved in tree bark do not move farther up from the ground as the tree grows

10 Plants are composed of two types of cells
During plant growth, meristem cells give rise to differentiated cells Meristem cells, like animal stem cells, are unspecialized and capable of mitotic cell division Some daughter cells lose the ability to divide and become differentiated cells, with specialized structures and functions Continued division of meristem cells keep the plant growing throughout its life Differentiated daughter cells form the non-growing parts of the plant, as leaves -

11 Where Growth Occurs Plants grow as a result of cell division and differentiation of meristem cells found in two general locations – Apical meristems - located at the tips of roots and shoots Growth produced by apical meristem cells is primary growth Increase in the height or length of a shoot or root, development of specialized parts of the plant - leaves and buds Lateral meristems (side meristems, cambium) - concentric cylinders of meristem cells

12 Animation: Primary Growth

13 Secondary Growth Many plants do not undergo secondary growth
Division of lateral meristem cells and differentiation of their daughter cells produce further concentric cylinders of secondary growth, an increase in the diameter and strength of roots and shoots Occurs in woody plants - deciduous trees, shrubs, conifers Some woody plants become very tall and thick and may live hundreds to thousands of years Many plants do not undergo secondary growth Plants that lack secondary growth are soft bodied, with flexible, fairly short stems These herbaceous, typically short-lived plants include lettuce, beans, lilies, and grasses

14 Tissues and Cell Types? As meristem cells differentiate, they produce a variety of cell types One or more specialized types of cells work together to perform a specific function, as conducting water and minerals = tissue Functional groups of more than one tissue = tissue systems Dermal tissue system covers the outer surface of the plant Ground tissue system makes up the body of young plants; its functions include photosynthesis, storage, and support Vascular tissue system transports fluids throughout the plant body

15 Tissues and Cell Types

16 Dermal Tissues Dermal tissue system covers the plant body
Two types of dermal tissues: epidermal tissue periderm

17 Epidermal Tissues Epidermal tissue forms the epidermis - outermost cell layer covering the leaves, stems, and roots of all young plants, also covers flowers, seeds, and fruit In herbaceous plants, it forms the outer covering of the entire plant body throughout its life Above ground - generally composed of tightly packed, thin-walled cells, covered with waterproof, waxy cuticle secreted by the epidermal cells The cuticle reduces the evaporation of water from the plant and helps protect it from the invasion of disease microorganisms Adjustable pores regulate the movement of water vapor, O2, and CO2 across the epidermis of leaves and young stems In contrast, the epidermal cells of roots are not covered with cuticle that would prevent them from absorbing water and minerals

18 Periderm Replaces epidermal tissue on the roots and stems of woody plants as they age Composed of multiple layers of cork cells on the outside of the root or stem and a layer of lateral meristem tissue - cork cambium - that generates the cells Cork cells produce thick, waterproof cell walls as they grow, then die as they reach maturity Because of multiple layers of waterproof cork cells on their surface, root segments that are covered with periderm help anchor the plant in the soil, but can not absorb water and minerals

19 Ground Tissue Compromises most of the young plant body
All of the tissue of the plant body except dermal and vascular tissues Three types of ground tissues are parenchyma, collenchyma, and sclerenchyma

20 Parenchyma Parenchyma - most abundant - makes up most of young plant body The cells - called parenchyma cells - have thin cell walls and are alive at maturity They carry out the plant’s metabolic activities, photosynthesis , secretion of hormones, food storage Potatoes, seeds, fruits, storage roots are packed with parenchyma cells that store sugars and starches Help to support the bodies of many plants, especially herbaceous plants Some cells can divide In addition to making up much of the ground tissue system, parenchyma cells are found in periderm and vascular tissues

21 Parenchyma stored starch thin cell wall
(a) Parenchyma cells in a white potato

22 Collenchyma Cells that are elongated, with thickened but flexible cell walls Alive at maturity, generally cannot divide Collenchyma tissue provides support for entire body of young and non-woody plants, the leaf stalks, or petioles, of all plants Celery stalks are thick petioles, are supported by “strings” composed of collenchyma cells

23 Collenenchyma thick cell wall (b) Collenchyma cells in a celery stalk

24 Sclerenchyma Composed of cells with thick, hardened cell walls Sclerenchyma cells support and strengthen the plant body; they die after they differentiate Their thick cell walls then remain as a source of support Sclerenchyma cells form nut shells and the outer covering of peach pits Scattered throughout the parenchyma cells in a pear, sclerenchyma cells give pears their gritty texture Sclerenchyma cells support vascular tissues and form an important component of wood

25 Sclerenenchyma thick cell wall (c) Sclerenchyma cells in a pear

26 The Vascular Tissue System
Transports water and nutrients Conducts water and dissolved substances throughout the body Consists of two conducting tissues: xylem and phloem

27 Xylem Transports water and dissolved minerals from the roots to the rest of the plant, only in one direction. In angiosperms, xylem contains supporting sclerenchyma fibers and two specialized conducting cell types: tracheids and vessel elements Both tracheids and vessel elements develop thick cell walls, then die as their final step of differentiation, leaving hollow tubes of nonliving cells wall

28 Xylem Tissues Tracheids - thin, elongated cells stacked atop one another Tapered, overlapping cells resemble the tips of hypodermic needles The ends and sides of tracheids contain pits - porous dimples in the walls that separate adjacent cells Because the cell wall in a pit is both thin and porous, water and minerals pass freely from one tracheid to another an adjacent vessel element Vessel elements - larger in diameter than tracheids, form pipelines called vessels Vessel elements are stacked end to end Their adjoining end walls may be connected by fairly large holes or the walls may disintegrate, leaving an open tube

29 Animation: Xylem Adaptations

30 Xylem tracheids pits end wall vessel element

31 Phloem Two cell types: sieve-tube elements and companion cells
Transports sugars and other organic molecules throughout the plant body Transports sugars, amino acids, and hormones—from structures that synthesize them to structures that need them Transports fluids up or down the plant, depending on the metabolic state of the parts of the plant at any given time Two cell types: sieve-tube elements and companion cells Sieve-tube elements - joined end to end to form pipes As sieve-tube elements mature, they lose their nuclei and other organelles, only a thin layer of cytoplasm lining the plasma membrane The junction between two sieve-tube elements is a sieve plate Membrane-lined pores connect the insides of two sieve-tube elements, allowing fluid to move from one cell to the next

32 Sieve-tube Cells Sieve-tube function requires an intact plasma membrane How, then, can sieve-tube elements maintain and repair their plasma membranes when they lack nuclei and most other organelles? Life support of sieve-tube elements is provided by smaller, adjacent companion cells, which are connected to sieve-tube elements by pores called plasmodesmata Companion cells help maintain the integrity of the sieve-tube elements by providing them with proteins and high-energy compounds such as ATP Like xylem, phloem also contains supporting sclerenchyma fibers

33 Phloem companion cell sieve plate companion cell sieve-tube element

34 Leaves Major photosynthetic structures of most plants
Their green color arises from chlorophyll molecules Shape and structure of leaves has evolved in response to environmental challenges that plants face in obtaining the essentials for photosynthesis: sunlight, carbon dioxide (CO2), and water Water is absorbed from the soil by the roots and transported to leaves by the xylem Assuming adequate water supply, maximum photosynthesis would occur in a porous leaf (allows CO2 to diffuse easily from air to the leaf) with a large surface area

35 Leaves are a compromise…
Land plants cannot always get enough water from soil On a hot, sunny day - large, porous leaf loses more water through evaporation than the plant could replace The leaves of flowering plants are an compromise between conflicting demands They have a large, waterproof surfaces with adjustable pores that can open and close to admit CO2 or restrict water evaporation

36 Angiosperm Leaves A broad, flat portion - the blade is connected to the stem by a stalk, or petiole The petiole positions the blade Inside, vascular tissues provide a conducting system between the leaf and the rest of the plant The epidermis regulates movement of gases in and out Leaf epidermis is a layer of nonphotosynthetic, transparent cells that secrete a waxy cuticle on the outer surfaces The cuticle is waterproof and reduces evaporation

37 Stomata (stoma) Adjustable pores in the cuticle and epidermis, they regulate the diffusion of CO2, O2, water vapor in and out Two sausage-shaped guard cells that enclose and adjust the size of the opening Unlike the other epidermal cells, guard cells contain chloroplasts and carry out photosynthesis

38 Functions of Leaves Photosynthesis occurs in mesophyll cells The transparent epidermal cells allow sunlight to reach the mesophyll (“middle of the leaf”), which consists of loosely packed cells containing chloroplasts Mesophyll cells carry out most of the photosynthesis of a leaf Air spaces between mesophyll cells allow CO2 from the atmosphere to diffuse to each cell and O2 produced during photosynthesis to diffuse away Many leaves possess two types of mesophyll cells—an upper layer of columnar palisade cells and a lower layer of irregularly shaped spongy cells

39 Vascular Bundles Veins transport water and nutrients throughout the leaf Vascular bundles (veins) contain xylem and phloem Conduct materials between leaf and the rest of the plant Veins send thin branches to each photosynthetic cell Xylem delivers water and minerals to the mesophyll cells of the leaf, and phloem carries away the sugar they produce during photosynthesis

40 A Typical Dicot Leaf petiole blade bundle-sheath cell cuticle upper
epidermis palisade layer mesophyll spongy layer lower epidermis xylem phloem cuticle stoma guard cell chloroplasts vascular bundle

41 Structures and Functions of Leaves
Temperature, availability of water and light have exerted selection pressure on leaves Dim light - the floor of a tropical rain forest - very large leaves, low light level and abundant water Desert-dwelling cacti have spines , no surface area for evaporation Plump leaves of succulents store water in the central vacuoles of their cells and are covered with a thick cuticle to reduces water evaporation Some plants have surprising structures and functions, including storing nutrients, capturing prey, or climbing Onions, Venus Flytraps, Pea plant tendrils

42 Specialized Leaves

43 Stems Support and separate the leaves, lifting them to the sunlight and air Stems transport water and dissolved minerals from the roots up to the leaves They also transport sugars produced in the photosynthetic parts of the shoot to the roots and other parts of the shoot, such as buds, flowers, and fruits

44 Adaptations of stems Potato eyes Strawberry runners
Grapes and ivies with grasping tendrils thorns

45 Cork

46 Functions of Roots Anchor plant Absorb water and mineral
Store water and food Dicots generally have taproots Monocots have fibrous root systems

47 Taproots and Fibrous Roots

48 Structures of Roots? 4 distinct regions Root cap Epidermis Cortex
Vascular cylinder

49 Primary Growth in Roots
epidermis root hair cortex endodermis of cortex pericycle xylem phloem vascular cylinder apical meristem root cap

50 Root Cap Primary growth in a root Protects apical meristem
Thick cell walls, lubricant Continuously replaced

51 Epidermis Permeable to water and minerals No cuticle
Epidermal cells grow root hairs to increase surface area

52 Root Hairs

53 Cortex Located between the epidermis and vascular cylinder
Large, loose packed parenchyma with porous cell walls Sugar is transported to these cells and stored as starch Innermost layer, endodermis circles vascular cylinder Caspian Strip (more later) – waxy on top bottom, sides but not inner/outer faces

54 Vascular Bundle - Pericycle
Pericycle – outermost layer Regulate movement of minerals and water into xylem Source of branching in roots Hormone release causes formation of branch root Punches out through epidermis, cortex by crushing and releasing enzymes Xylem and Phloem

55 Branch Roots

56 Specialized Roots

57 Secondary Growth Similar but not identical to secondary growth in stems Vascular cambium produces secondary xylem and phloem in the root interior Cork cambium produces cork cells on the outside of the root

58 Essential Nutrients Plants only need inorganic nutrients because they can make their own organic molecules Macronutrients – needed in large quantity Micronutrients - <1% total nutrients needed CO2 - O2 - H Minerals (K, Ca) Ionic compounds – nitrate, phosphate Water

59 Water is crucial Transport minerals, sugars, hormones and other organic molecules Plants require a large amount of water Source is soil

60 Roots Transport Minerals
Absorb mineral from soil and transport to xylem Minerals must be dissolved in soil water Transported from root to shoot in tracheids and vessel elements of xylem

61 Young Root Structure Living cells Extracellular space
Tracheids and vessel elements (dead) Cell walls are all very porous Caspian strip divides extracellular space into two compartments – inside (vascular bundle) and outside

62 Mineral and Water Uptake by Roots
vascular cylinder cortex epidermis air soil particles pericycle endodermis xylem 5 water 4 3 1 2 root hair plasmodesmata cell walls (a) Pathways of mineral and water uptake endodermal cells Casparian strip (b) Endodermal cells, showing the Casparian strip

63 Mineral and water uptake
Minerals dissolved in water fill space between cells (blue) Minerals are actively transported across plasma membrane of root hairs, epidermal, cortex, and outside face of endodermal cells; water follows by osmosis (black) Minerals diffuse from cell to cell through plasmodesmata (red) Minerals diffuse or are actively transported across plasma membanes of pericycle cells; water follows by osmosis Minerals and water enter tracheids and vessel elements of xylem (blue)

64 Importance of the caspian strip
Soil water in the outer root compartment has low concentration of mineral Inner compartment has higher concentration = diffusion gradient The caspian strip prevents movement of minerals from inner outer compartments

65 Author Animation: Xylem Transport

66 Root Pressure Water moves by osmosis from the soil, across plasma membranes and into the tracheids and vessel elements of the roots Sometimes this pressure is so strong it causes root pressure – water entering pushes minerals up the root into the shoot and the water droplets can be visible on the leaves This is influenced by transpiration –evaporation of water from the leaves

67 Root Pressure

68 Symbiotic Relationships
Mutually beneficial relationships Fungal mycorrhizae – fungi in a symbiotic relationship with plant roots. Fungal strands twine between roots, increasing area of root in contact with soil Some fungi can extract elements that plants cannot, ie. Phosphates Fungus receives sugars, amino acids, vitamins from plant Desert and high altitude locations In some forested areas the mycorrhizae interlink trees of different species, allowing nutrient exchange between them

69 Mycorrhizae: A Root–Fungus Symbiosis

70 Nitrogen-fixing bacteria
Plants can only use N in form of ammonia or nitrate Legumes – peas, alfalfa, soy beans Symbiotic relationship with bacteria that are able to fix nitrogen (N2 NH3) Bacteria enter cell and move to cortex where they form a nodule Use plant nutrients

71 Nodules House Nitrogen-Fixing Bacteria
nitrogen-fixing bacteria within cortex cells of nodules nodule epidermis

72 Transpiration 90% of water absorbed is lost through the stomata of the leaves, minerals are carried along with the water Cohesion – tension theory = water is pulled up the tree by transpiration Cohesion – attraction between water molecules, forms a chain-like column within the xylem Tension – chain of water is pulled up xylem by tension produced by evaporation from leaves Redwood trees that are 350 ft. tall

73 The Cohesion–Tension Theory
Water evaporates through the stomata of leaves 1 water molecules flow of water Cohesion of water molecules to one another by hydrogen bonds creates a “water chain” 2 Water enters the vascular cylinder of the root 3

74 Author Animation: Cohesion and Adhesion

75 Amazon Rain Forest Warm weather and abundant rainfall
Supports hundreds of trees per acre Humidity partially due to transpiration When clearcut, local climate is much drier and hotter Read page 858

76 Stomata Regulation Mechanically – how is the size changed?
Physiologically – how do they respond to stimuli? Two guard cells, slightly curved. Cellulose fibers encircle the cells K+ enters cells in response to light and CO2 conc., water follows by osmosis Cellulose belts prevent cells from getting fatter so they get longer, curve outward – open central pore Closes when it loses water

77 Stomata

78 How Guard Cells Open a Stoma
K+ enters the guard cells (red arrows) 1 K+ ions Water follows by osmosis (blue arrows) 2 cellulose “belts” The guard cells lengthen and bend outward 3 pore The pore opens 4 guard cells (a) Closed stoma (b) Opening a stoma

79 How is sugar transported?
Synthesized in leaves, carried by phloem Botanists use aphids to learn how phloem works Chemical analysis of phloem fluid = 12-20% sugar, +amino acids, protein and hormones

80 Aphids Feed on the Sugary Fluid in Phloem Sieve Tubes

81 Pressure-flow theory Differences in water pressure drive flow of fluid through sieve tubes Pressure differences are created by the production and use of sugars Sugar source – synthesizes more than uses Sugar sink – uses more than it synthesizes May be source or sink depending on season Roots, sink – summer (conv. sugar to starch) Roots, source – following spring (conv. starch to sugar)

82 How it works Sugar produce in source cell, transported to phloem
Water from xylem follows sugar into phloem, increasing pressure Water pressure drives fluid to regions of lower pressure Cells of sugar sink transport sugar out of phloem, water follows by osmosis = lower pressure

83 The Pressure-Flow Theory of Sugar Transport in Phloem
phloem sieve tube xylem vessel sunlight 1 sugar source 2 sugar source cell 3 sugar sink 4 sugar sink cell Fig

84 Author Animation: Phloem Transport

85 Why do leaves turn color in the fall?
Fall - temperatures cool, days are long and sun is bright Photosynthetic pathways are less efficient, leaf cannot use all light available Excess light harms chloroplasts Red pigmented leaves – anthocyanin – are better protected against intense light Why protect? Complex molecules in the leaves are broken down and stored in cells in the root and stem. Photosynthesis must continue to provide energy for this process

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