Lecture 5 Outline (Ch. 35) I. Overview – Plant Systems II. Plant cell types & tissues Cell Types: Parenchyma, Collenchyma, Sclerenchyma A. Dermal B. Vascular C. Ground III. Plant organs A. Roots B. Stems C. Leaves IV. Plant Growth A. Meristems B. Primary vs. secondary V. Preparation for next lecture Plant Structure, Growth, Development Plants are notably different from animals: 1. SA:V ratio 2. Mobility 3. Growth 4. Response to environment 5. Cell structure Setting the scene - animal bodies Cells Tissues Organs Systems Plant “bodies” Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells Shoot system Leaf Stem Three Basic Plant Organs: Roots, Stems, and Leaves (also flowers, branches) Root system Plant Tissues • Each plant organ has dermal, vascular, and ground tissues • Each of these three categories forms a system – Roots – Shoots – Vascular Dermal tissue Ground tissue Vascular tissue Plant Tissues 1) Dermal Tissues • Outer covering • Protection 2) Vascular Tissues • “Vessels” throughout plant • Transport materials 3) Ground Tissues • “Body” of plant • Photosynthesis; storage; support Three basic cell types: Parenchyma Collenchyma Sclerenchyma What type of tissue transports fluids in plants? A. B. C. D. E. Dermal Roots Vascular Stems Ground Plant Cell Types Plant cell structure recap Cell wall, plasmodesmata Primary wall (some have secondary wall), middle lamella Plant Cell Types 1) Parenchyma (most abundant): Flexible, thin-walled cells; living • plant metabolism: Photosynthesis; hormone secretion; sugar storage Parenchyma cells in Elodea leaf,(w/chloroplasts) • thin wall permeable to gasses • large central vacuole • able to divide and differentiate Plant Cell Types 2) Collenchyma: Thick-walled (uneven); living • Offers support (flexible & strong) • Able to elongate • Grouped in strands, lack secondary wall Collenchyma cells sunflower Plant Cell Types 3) Sclerenchyma: Thick, hard-walled; Dead • Offer support (e.g. hemp Sclereid cells in pear (LM) Cell wall Fiber cells in ash tree fibers; nut shells) • Thick secondary walls with lignin • Rigid (cannot elongate) • Two types – sclereids and fibers Which is a plant cell type? A. B. C. D. E. secondary vascular ground collenchyma leaves Plant Tissues - Dermis Dermal Tissue System (Covering of Plant): 1) Epidermal Tissue (epidermis): Outer layer Cuticle: Waxy covering reduces evaporation/ predation Root Hairs: extended root surface - Increase absorption 2) Peridermal Tissue (periderm): • Only in woody plants (“bark = dead cells”) • Protection; support Plant Tissues - Dermis Special Dermal Cells – Trichomes & Root hairs • Trichomes – Hairlike outgrowths of epidermis – Keep leaf surfaces cool and reduce evaporation • Roots hairs – Tube extensions from epidermal cells – Greatly increase the root’s surface area for absorption Plant Tissues - Dermis Special Dermal Cells – Guard Cells Stomata Guard cells Epidermal cell a. 4 µm Stoma Epidermal cell Guard cells b. 71 µm c. 200 µm Paired sausage-shaped cells Flank a stoma – epidermal opening • Passageway for oxygen, carbon dioxide, and water vapor Plant Tissues - Vascular Vascular tissues made up of multiple cell types: Arranged in multiple bundles or central cylinder Xylem – water and nutrients Phloem – dissolved sugars and metabolites Plant Tissues - Vascular 1) Xylem (dead at maturity): water and minerals roots to shoots A) B) C) Tracheids: Narrow, tube-like cells Vessel Elements: Wide, tube-like cells Fibers Plant Tissues - Vascular 1) Xylem: Tracheids: - Most vascular plants - Long, thin, tapered ends, lignified secondary walls - Water moves cell to cell through pits Vessel elements: - Wider and shorter - Perforation plates ends of vessel elements - water flows freely though perforation plates Plant Tissues - Vascular 2) Phloem (living at maturity) cells: A) Sieve Tubes: Wide, tube-like cells B) Companion Cells: support and regulate sieve tubes Plant Tissues - Vascular 2) Phloem (living at maturity) - Moves water, sugar, amino acids & hormones Sieve tube elements/members • Living parenchyma • Long narrow cells stack end to end • Pores in end walls (sieve plates) • Lack most cellular structures including: • Distinct vacuole, Some cytoskeletal elements, Nucleus, Ribosomes Companion Cells: • Adjacent to every sieve tube element • Non-conducting. • Regulate both cells • Connected by numerous plasmodesmata Vasculature - Comparisons Monocots and dicots differ in the arrangement of vessels in the roots and stems Dicots Monocots Stem Root Plant Tissues – Ground Tissue • Tissues that are neither dermal nor vascular are ground tissue • Ground tissue internal to the vascular tissue is pith; ground tissue external to the vascular tissue is cortex • Ground tissue includes cells specialized for storage, photosynthesis, and support Roots - Overview • Roots need sugars from photosynthesis; • Shoots rely on water and minerals absorbed by the root system • Root Roles: - Anchoring the plant - Absorbing minerals and water - Storing organic nutrients Roots - Comparisons Taproots: Typical of dicots, primary root forms and small branch roots grow from it Fibrous roots: In monocots mostly, primary root dies, replaced by new roots from stem Roots – Structure and Development • Four regions: – Root cap Protection, gravity detection – Zone of cell division Mitotic divisions – Zone of elongation Cells lengthen, no division – Zone of maturation Cells differentiate, outer layer becomes dermis Roots – Structure and Development In maturation zone, Casparian strip forms – waterproof barrier material surrounding vasculature Roots – Structure and Development Epidermis Cortex Monocot Endodermis Location of Casparian strip Primary phloem Pericycle Primary xylem Pith 1250 µm 385 µm Endodermis Location of Casparian strip Endodermis Eudicot Primary xylem Cortex Primary phloem Epidermis Pericycle 48 µm 8 µm Prop roots Roots – Many Plants Have Modified Roots “Strangling” aerial roots Storage roots Buttress roots Pneumatophores Water storage Stems - Overview Stem: an organ made of – An alternating system of nodes, points at which leaves attach – Internodes, stem length between nodes • Axillary bud - structure that can form a lateral shoot, or branch • Apical/terminal bud located near the shoot tip, lengthens a shoot • Apical dominance maintains dormancy in most nonapical buds Apical bud Node Internode Apical bud Vegetative shoot Axillary bud Stem Shoot system Vasculature - Stems • In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring Phloem Xylem Sclerenchyma (fiber cells) Ground tissue Ground tissue connecting pith to cortex Pith Epidermis Key to labels Cortex Epidermis Vascular bundle Dermal Vascular bundles Ground 1 mm (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots) Dicot Vascular 1 mm (b) Cross section of stem with scattered vascular bundles (typical of monocots) Monocot Stems – Structure and Development • Stems have all three types of plant tissue • Grow by division at meristems – Develop into leaves, other shoots, and even flowers • Leaves may be arranged in one of three ways Stems – Many Plants Have Modified Stems Rhizomes Bulbs Storage leaves Stem Stolons Stolon Tubers Leaves - Overview The leaf is the main photosynthetic organ of most vascular plants Shoot system Leaves generally have Leaf Blade Petiole a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem Leaves – Structure and Development • Leaves are several layers thick – each with different cell types Leaves – Structure and Development • Most dicots have 2 types of mesophyll – Palisade mesophyll high photosynthesis – Spongy mesophyll air spaces for gas & water exchange • Monocot leaves have 1 type of mesophyll Leaves • Leaf epidermis contains stomata - allow CO2 exchange • Stomata flanked by two guard cells, control open vs. closed Guard cells Key to labels Dermal Ground Cuticle Vascular 50 µm Stomatal pore Epidermal cell Sclerenchyma fibers Stoma (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Palisade mesophyll 100 µm Spongy mesophyll Bundlesheath cell Lower epidermis Cuticle Xylem Vein Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Air spaces Guard cells (c) Cross section of a lilac (Syringa)) leaf (LM) Leaves - Comparisons Monocots and dicots differ in the arrangement of veins, the vascular tissue of leaves Most dicots have branch-like veins and palmate leaf shape Monocots have parallel leaf veins and longer, slender blades Leaves – Plants have modified leaves for various functions Tendrils Spines Storage leaves Reproductive leaves Bracts Plant Classification – Monocots vs. Dicots Basic categories of plants based on structure and function Plant Growth Plant Growth: 1) Indeterminate: Grow throughout life 2) Growth at “tips” (length) and at “hips” (girth) Growth patterns in plant: 1) Meristem Cells: Dividing Cells 2) Differentiated Cells: Cells specialized in structure & role • Form stable, permanent part of plant Plant Growth 1) Primary Growth: • Apical Meristems: Mitotic cells at “tips” of roots / stems length 1) Increased length 2) Specialized structures (e.g. fruits) 2) Secondary Growth: girth • Lateral Meristems: Mitotic cells “hips” of plant Responsible for increases in stem/root diameter Plant Growth Shoot apical meristem Leaf primordia Young leaf Developing vascular strand Axillary bud meristems Plant Growth Two lateral meristems: vascular cambium and cork cambium Primary growth in stems Epidermis Cortex Shoot tip (shoot apical meristem and young leaves) Primary phloem Primary xylem Pith Lateral meristems: Vascular cambium Cork cambium Secondary growth in stems Periderm Axillary bud meristem Cork cambium Cortex Root apical meristems Pith Primary xylem Secondary xylem Vascular cambium Primary phloem Secondary phloem Plant Growth Stem – Secondary Growth: • thicker, stronger stems Vascular Cambium: between primary xylem and phloem primary phloem vascular cambium primary xylem epidermis Produces inside stem: A) Secondary xylem - moves H2O, inward B) Secondary phloem - moves sugars, outward pith cortex primary xylem dividing vascular cambium primary phloem Vascular Cambium: Plant Growth Secondary growth secondary phloem primary phloem primary xylem secondary xylem primary xylem new secondary xylem new secondary phloem vascular cambium dividing vascular cambium primary phloem pith cortex Vascular cambium Growth X X C P P X X C P Vascular cambium Secondary xylem Secondary phloem X C P C X C C C After one year of growth After two years of growth A cross section of what tissue is pictured? A. B. C. D. Monocot root Dicot root Monocot stem Dicot stem Things To Do After Lecture 5… Reading and Preparation: 1. Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. 2. Ch. 35 Self-Quiz: #1, 3, 6, 7 (correct answers in back of book) 3. Read chapter 35, focus on material covered in lecture (terms, concepts, and figures!) 4. Skim next lecture. “HOMEWORK” (NOT COLLECTED – but things to think about for studying): 1. Compare and contrast monocots and dicots. 2. List the different types of plant cells and describe which tissues and organs they make up, including roles for each organ. 3. Explain the different between apical and lateral meristems and how growth occurs. 4. Discuss the composition of bark and it’s function for plants (do all plants have this tissue?)