Transcript cell types
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 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: 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 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 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 Systems • 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 - 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 – 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 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 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 Plant Organs: 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 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 Plant Organs: Roots – Vasculature Epidermis Dicot Monocot Cortex Endodermis Vascular cylinder 100 m (a) Root with xylem and phloem in the center Pericycle Core of parenchyma cells Xylem Phloem 100 m (b) Root with parenchyma in the center 50 m Endodermis Pericycle Xylem Phloem Key to labels Dermal Ground Vascular 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 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 – Many Plants Have Modified Stems Rhizomes Bulbs Storage leaves Stem Stolons Stolon Tubers Plant Organs: 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 - joins the leaf to node of the stem Leaves – Structure • Leaves are several layers thick – different cell types Key to labels Sclerenchyma fibers Cuticle Dermal Ground Vascular Stoma Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermis Xylem Phloem Vein Guard cells Cuticle Plant Organs: Leaves • Leaf epidermis contains stomata allow CO2 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 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 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 Secondary phloem First cork cambium Cork Produces inside stem: A) Secondary xylem - moves H2O, inward B) Secondary phloem - moves sugars, outward Vascular Cambium: Plant Growth Pith Primary xylem Vascular cambium Primary phloem Cortex Epidermis Vascular ray Secondary xylem Secondary phloem First cork cambium Cork 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?)