Lecture 5 Outline (Ch. 35) I. Overview Plant Systems II. Plant cell types III. Tissues 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 1
Setting the scene - animal bodies Cells Tissues Organs Systems 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: Parenchyma cells in Elodea leaf,(w/chloroplasts) Photosynthesis; hormone secretion; sugar storage thin wall permeable to gasses large central vacuole able to divide and differentiate 2
2) Collenchyma: Plant Cell Types Thick-walled (uneven); living Collenchyma cells sunflower Offers support (flexible & strong) Able to elongate Grouped in strands, lack secondary wall 3) Sclerenchyma: Thick, hard-walled; Dead Cell wall Plant Cell Types Sclereid cells in pear (LM) Offer support (e.g. hemp fibers; nut shells) Thick secondary walls with lignin Rigid (cannot elongate) Two types sclereids and fibers Fiber cells in ash tree 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 Plant Tissues 3
Plant bodies Plants, like multicellular animals, have organs composed of different tissues, which in turn are composed of cells Shoot system Leaf Three Basic Plant Organs: Stem Roots, Stems, and Leaves (also flowers, branches) Root system Each plant organ has dermal, vascular, and ground tissues Plant Systems Each of these three categories forms a system Roots Shoots Vascular Dermal tissue Ground tissue Vascular tissue 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 4
Plant Tissues - Dermis Special Dermal Cells Trichomes & Root hairs Trichomes Hair-like 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 a. c. Guard cells Epidermal cell 4 µm 200 µm b. Stoma Guard cells Epidermal cell 71 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 5
1) Xylem (dead at maturity): water and minerals roots to shoots A) Tracheids: Narrow, tube-like cells B) Vessel Elements: Wide, tube-like cells C) 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 Plant Tissues - Vascular 2) Phloem (living at maturity) cells: A) Sieve Tubes: Wide, tube-like cells B) Companion Cells: support and regulate sieve tubes 6
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 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 Plant Organs: 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 7
Taproots: Plant Organs: Roots - Comparisons Fibrous roots: Typical of dicots, primary root forms and small branch roots grow from it In monocots mostly, primary root dies, replaced by new roots from stem Plant Organs: 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 Plant Organs: Roots Structure and Development In maturation zone, Casparian strip forms waterproof barrier material surrounding vasculature 8
Dicot Plant Organs: Roots Vasculature 100 m (a) Root with xylem and phloem in the center 50 m Epidermis Cortex Endodermis Vascular cylinder Pericycle Core of parenchyma cells Xylem Phloem Endodermis Pericycle Xylem Phloem 100 m (b) Root with parenchyma in the center Key to labels Dermal Ground Vascular Monocot Prop roots Roots Many Plants Have Modified Roots Strangling aerial roots Storage roots Buttress roots Pneumatophores Water storage Plant Organs: Stems - Overview Stem: an organ made of Alternating nodes, points of leaf attachment Internodes, stem length between nodes Axillary bud - can form a lateral shoot/branch Apical(terminal) bud - near the shoot tip, lengthens a shoot Apical dominance maintains dormancy in most non-apical buds Apical bud Node Internode Apical bud Vegetative shoot Axillary bud Stem Shoot system 9
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 connecting pith to cortex Ground tissue Pith Epidermis Epidermis Cortex Vascular bundle 1 mm (a) Cross section of stem with vascular bundles forming a ring (typical of eudicots) Dicot Key to labels Vascular Dermal bundles Ground Vascular 1 mm (b) Cross section of stem with scattered vascular bundles (typical of monocots) Monocot Rhizomes Stems Many Plants Have Modified Stems Bulbs Storage leaves Stolons Stem Stolon Tubers Plant Organs: Leaves - Overview The leaf is the main photosynthetic organ of most vascular plants Leaves generally have a flattened blade Leaf Blade Petiole Shoot system and a stalk called the petiole - joins the leaf to node of the stem 10
Leaves Structure Leaves are several layers thick different cell types Key to labels Dermal Ground Vascular Cuticle Sclerenchyma fibers Stoma Upper epidermis Palisade mesophyll Spongy mesophyll Xylem Phloem Guard cells Vein Lower epidermis Cuticle Plant Organs: Leaves Leaf epidermis contains stomata - allow CO 2 exchange Stomata flanked by two guard cells, control open vs. closed Plant Organs: 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 11
Tendrils Leaves Plants have modified leaves for various functions 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 12
Plant Growth 1) Primary Growth: Apical Meristems: Mitotic cells at tips of roots / stems 1) Increased length 2) Specialized structures (e.g. fruits) length 2) Secondary Growth: Lateral Meristems: Mitotic cells hips of plant girth Responsible for increases in stem/root diameter Plant Growth in woody plants Two lateral meristems: vascular cambium and cork cambium Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis thicker, stronger stems Vascular Cambium: between primary xylem and phloem Plant Growth Stem Secondary Growth: Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular ray Secondary xylem Cork Secondary phloem First cork cambium Produces inside stem: A) Secondary xylem - moves H 2 O, inward B) Secondary phloem - moves sugars, outward 13
Vascular Cambium: Plant Growth Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular ray Secondary xylem Cork Secondary phloem First cork cambium Most recent cork cambium Cork Bark Layers of periderm 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 difference 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?) 14