Monocots Dicots 6/4/2012 Plants Plant Form and Function Chapter 17 Herbaceous (nonwoody) In temperate climates, aerial parts die back Woody In temperate climates, aerial parts persist The Plant Body Functions of: Roots Stem Leaves Flowering plants can be divided into two groups: Monocots: grasses, lilies, palms, and orchids Dicots: deciduous trees, bushes, and many garden flowers Flowers Leaves Stems Roots Seeds Tissue Systems embryo cotyledon Integrated throughout the plant body provide continuity from organ to organ Flower parts are in threes or multiples of three Leaves have smooth edges, often narrow, with parallel veins bundles are scattered throughout the stem Monocots have a fibrous root system The seed has one cotyledon (seed leaf) embryo cotyledons Plant body has 3 tissue systems 1. ground 2. vascular 3. dermal Flower parts are in fours or fives or multiples of four or five Leaves are palmate (handlike) or oval with netlike veins bundles are arranged in a ring around the stem Dicots have a taproot system The seed has two cotyledons (seed leaves) Fig. 17-2 1
Ground Tissue System Consists of 3 tissues, many functions parenchyma tissue collenchyma tissue sclerenchyma tissue Ground Tissue: Parenchyma Tissue Composed of living parenchyma cells with thin primary cell walls Functions photosynthesis storage Secretion Ground Tissue: Collenchyma Tissue Consists of collenchyma cells with unevenly thickened primary cell walls Intercellular space Parenchyma cells Vacuole Nucleus Cytoplasm Cell wall Fig. 32-4a, p. 706 Provides flexible structural support Strings of celery Thickened corner of cell wall Ground Tissue: Sclerenchyma Tissue Composed of sclerenchyma cells sclereids or fibers Thick cell walls Sclerenchyma cells often dead at maturity provide structural support Collenchyma cells Nucleus Cytoplasm Vacuole Fig. 32-4b, p. 706 2
Tissue System Conducts materials throughout plant body Lumen Provides strength and support Sclerenchyma cells Cell wall Fig. 32-4c, p. 706 Tissue: Xylem Complex tissue, conducts water and dissolved minerals 2 types of cells of xylem tracheids vessel elements Xylem End wall with perforations Pits Cell wall Lumen (a) Tracheid. (b) Vessel element Fig. 32-5ab, p. 708 Tissue: Phloem Complex tissue, conducts sugar in solution 2 types of cells of 1. sieve tube elements 2. assisted by companion cells Phloem Sieve plate with pores Sieve tube element Phloem parenchyma cells Lateral sieve area Plasmodesma Companion cell (c) Sieve tube element. (d) Phloem tissue. Fig. 32-5cd, p. 708 3
Dermal Tissue System Outer protective covering of plant body Epidermis: complex tissue covers herbaceous plant body Periderm: complex tissue covers woody parts of plant body Dermal Tissue: Epidermis Waxy cuticle reduces water loss secreted by epidermis covering aerial parts Stomata permit gas exchange between shoot system and atmosphere outgrowths or hairs many sizes, shapes, and functions Growth in Plants Localized in specific regions (meristems) Involves 3 processes: - cell division - cell elongation - cell differentiation Primary Growth vs. Growth Primary Growth Increase in stem or root length occurs in all plants Apical meristems at tips of roots and shoots within buds of stems Responsible for primary growth Root hairs Area of cell maturation Herbaceous Stems Epidermis: protective layer covered by a waterconserving cuticle Xylem: conducts water and dissolved minerals Phloem: conducts dissolved sugar Cortex, pith, and ground tissue: function primarily for storage & support Root cap Area of cell elongation Apical meristem (Area of cell division) Fig. 32-7, p. 710 4
Basic Tissues in Herbaceous Stems Herbaceous Stems Herbaceous eudicot stems vascular bundles arranged in a circle (in cross section) distinct cortex and pith Monocot stems vascular bundles scattered in ground tissue Pith Cortex Ground tissue Herbaceous Dicot Stem Monocot Stem (meristematic) Ground tissue bundles Epidermis 500 µm Fig. 34-3a, p. 734 5
Cortex cells Monocot Root Endodermis cell Pericycle cell Phloem cell Xylem vessel elements dicot root 25 µm Fig. 35-3b, p. 751 Apical Primary Lateral meristems tissue meristems tissues Meristematic cells Primary xylem Primary Cortex Pith Epidermis Cork xylem (wood) (inner bark) Periderm Growth Increase in stem or root girth (thickness) Woody plants only! Mitosis of meristematic at leteral meristems (not apical meristems) throughout length of older stems and roots Two Lateral Meristems responsible for secondary growth 1. vascular 2. cork Cork : outer = cork cells; inner = cork parenchyma cork cells & parenchyma = PERIDERM Inner bark (secondary ) Growth Production of secondary tissues, wood, bark occurs in some flowering plants (woody dicots) and all cone-bearing trees divides in two directions secondary xylem (to the inside) secondary (to the outside) Bark Wood (secondary xylem) Fig. 32-9, p. 712 6
Time 6/4/2012 Cambium Primary xylem Epidermis Primary Pith Cortex Fig. 34-4a, p. 735 Remnant of primary primary xylem Remnant of cortex pith epidermis (inner bark) xylem (wood) Periderm (outer bark) xylem (wood) primary xylem pith Periderm (outer bark; remnants of primary, cortex and epidermis are gradually crushed or turn apart and sloughed off) (inner bark) Fig. 34-4b, p. 735 Fig. 34-4c, p. 735 1X2X3X4X 2P1P Cork Cambium 1X2X3X 2P1P Lateral meristem that produces bark cork parenchyma and cork cells 1X2X xylem 1X 2X 1X 1X 1P 2P1P 1P cell Second division of vascular forms a cell. Division of vascular forms two cells, one xylem cell and one vascular cell. cell when secondary growth begins. Fig. 34-5, p. 736 Cork cells (cork) to outside of cork Cork parenchyma to inside of cork primarily for storage in a woody stem 7
Primary Pith xylem Annual ring of secondary xylem xylem (wood) Periderm and remnants of primary, cortex, and epidermis Expanded ray Xylem ray Heartwood Sapwood 0.5 mm Fig. 34-6, p. 737 Fig. 34-8, p. 739 Cross section of 3-year-old Tilia stem Summerwood Palisade mesophyll Vein (vascular bundle) Spongy mesophyll Cuticle Upper epidermis Springwood Annual ring of xylem Stoma Bundle sheath Xylem Phloem Airspace 100 µm Summerwood of preceding year Fig. 34-9, p. 739 Stoma Guard cells Lower epidermis Fig. 33-3, p. 718 Open Closed Stoma Guard cells Subsidiary cells Fig. 33-7a, p. 722 8
Transport Most water that plant absorbs is transpired into atmosphere. Water Movement Water and dissolved minerals move from soil into root tissues (epidermis, cortex) Sugar molecules from photosynthesis are transported in throughout plant, including into roots. Once inside roots, water and minerals are transported upward in xylem to stems, leaves, flowers, fruits, and seeds. Roots obtain water and dissolved minerals from soil. Water and minerals move upward, from root xylem to stem xylem to leaf xylem Water entering leaf exits leaf veins and passes into atmosphere (Transpiration) Stepped Art Fig. 34-10, p. 740 Tension Cohesion Model Explains rise of water even in the tallest plants! Transpiration evaporative pull causes tension at top of plant Column of water pulled up through the plant remains unbroken due to cohesive (together) and adhesive (others) properties of water Sugar Translocation Dissolved sugar is moved upward or downward in from source area of excess sugar (usually a leaf) to a sink (area of storage or sugar use: roots, apical meristems, fruits, seeds) Sucrose is predominant sugar transported in Pressure Flow Hypothesis Explains movement of materials in Companion cells actively load sugar into sieve tubes at source requires ATP ATP energy pumps protons out of sieve tube elements Source Pressure-flow theory Sucrose loaded and unloaded requires ATP Water moves osmotically ATP Sink 9