lecture

lecture CH 35 Plant Structure and Growth Some goals for this lecture: 1) List the Characteristics of an angiosperm. 2) Explain the differences between monocots and dicots. 3) Describe how plant cells divide and grow. 4) Explain the types and importance of Sclerenchyma, tracheids and vessel elements. 5) What is the difference between simple and complex tissues. 6) Be able to describe the difference between annual, biennial and perennial plants. 7) Explain how wood forms. 8) Be able to draw a diagram describing the basic structure of a root, stem and leaf. 1.Outline: The first humans in their everyday activity learned to identify eatable and poisonous plants. Some historians say that we had a very active role in applying the selective pressure that created our crop plants. Currently we are looking for new plants that may contain the gene to produce a drug which is a cure for Cancer, Aids or the common flue. Wouldn’t it be sad if this plant existed in a tropical rain forest that was cut down. You have heard it before, but we will emphasize it again, that our genetic resources are not a renewable resource. Once a plant species is dead, it is extinct forever. 2. Plant biology reflects the major themes in the study of life A. By studying a simple plant (Arabidopsis) on a molecular level we gain an understanding of all plants. B. The structure and function of plants is the result of interactions with the environment over long and short term time scales. C. While plants and animals faced many of the same problems in adapting to the terrestrial environment (support, internal transport) they solved these problems in different ways. 1) these different ways are a good indication that we originated from different ancestors. Lets now look at what the plants have done in their journy from the protists. 3. A plants root and shoot systems are evolutionary adaptations to living on land 1. Their exist two levels of plant architecture: a. Morphology = The study of the external structure of plants (e.g. arrangement of a flower) b. Anatomy = the study of the internal structure of plants (e.g. arrangement of the cells and tissues in a leaf) 2. Angiosperms are the most abundant and widespread of plants a. Have flower (adaptations for reproduction and seed dispersal) b. Two taxonomic divisions (1) Monocots= one seed leaves (2) Dicots= two seed ;eaves 3. Terrestrial plants have a divided habitat and divided structures that enter the habitat a. Air is a source of CO2 and sunlight b. soil is a source of water and minerals. A. The root system of plants: 1. Are adapted to a. anchor plant b. absorb and conduct water and nutrients c. store food 2. Types of root systems a. Taproot system (in many dicots) (1) one large vertical root produces many smaller secondary roots (2) provides anchorage and food storage b. fibrous root system (monocots, palms, bamboo, grasses) (1) mat of threadlike roots spread below soil surface (2) lots of surface area for exposure to soil water and minerals (3) fibers are concentrated in upper reaches of soil, where they help prevent erosion c. Root hairs - increase the surface area of the root (1) most numerous near root tips, are extensions of a single cell. (2) water and mineral absorption is enhanced by mycorrhizae d. Adventitious roots = roots arising from above ground stem or leaves (1) May help prop up plant, and helps extract extra nutrients B. The shoot system 1. Stems a. Nodes = Points where leaves are attached to stems b. Internodes = stem segments between the nodes c. Axillary bud = An embryonic side shoot found in the angle formed by each leaf and stem: usually dormant d. Terminal Bud = Bud on a shoot tip, usually has developing leaves and a compact series of nodes and internodes e. Apical dominance growth of shoot is concentrated at the apex of the shoot. Is an evolutionary adaptation to increase exposure of plants to light  Axillary buds will grow under certatin conditions and after damage or removeal of the apical bud. f. Stem modifications (1) Stolons = horizontal stems growing along surface of the ground (strawberries) (2) Rhizomes = stems growing underground (potato tubers) (3) Bulbs= vertical underground shoots with leaf bases modified for food storage (onions) 2. Leaves: Modifications include bud scales, bulb scales spines, tendrils bracts, sepals and petals. (Megaphyll) a. Main photosynthetic organ of the plant (1) shaped as a flattened blade joined to the node of stem by a petiole (2) Monocot have parallel major veins running the length of the blade (3) Dicots have a network of major veins (4) all leaves have numerous minor cross veins b. Classification of leaf arrangement on stem (1) Opposite - 2 leaves at each node 180' apart (2) alternate - each node has one leaf at adjacent nodes on opposite sides (3) Whorled - each node has 3 or more leaves attached c. other classifications (1) simple leaf - one undivided blade (2) compound leaf - divided into several leaflets (3) by shape (a) lanceolate (b)oval (c)cordate (hear shaped) (d) triangular (4) leaf margin (a) entire (smooth) (b) undulate (c) serrate (d) lobed d. Leaves adapted for non photosynthetic functions (1) Tendrils modified leaflets that cling to supports (2) spines of cacti function in protection (3) succulent leaves modified for storing water (4) brightly colored leaves to attract pollinators 4. The types of plant cells and their sepecialized functions A. The types of plant cells  Protoplast = contents of a plant cell exclusive of the cell wall; 1. Parenchyma cells are the least specialized a walls (1) primary are thin and flexible (2) secondary are absent b. protoplast has a large central vacuole c. function of these types of cells (1) synthesizing and storing organic products (a) stems and roots with/ colorless plastids store starch (2) photosynthesis occurs in the chloroplasts of mesophyll cells d. Most mature cells do not divide (1) Immature cells will retain ability to divide and differentiate 1. Collenchyma Cells a. walls (1) primary is thicker and is uneven thickness (2) also lacks secondary cell wall b. usually grouped in strands or cylinders to support young parts of plants c. living cells elongate as the stems and leaves they support grow 2. Sclerenchyma Cells a. function in support b. walls (1) thick secondary walls strengthened by lignin c. lack protoplast at functional maturity, do not grow once made d. major forms (1) fibers= long slender tapered cells occurring in bundles (2) Schlerids= shorter irregularly shaped cells 3. Tracheids and Vessel elements: Water-Conducting Cells a. Xylem consists of two cell types (a) Both are deposited in a spiral or ring pattern, allowing stretching in parts of the plant that is still growing (b) are often still functional when the cell itself is no longer living. (c) Make up most of the structures we call wood. (1) Tracheids- long thin tapered cells having lignin hardened secondary walls with pits (a) water flow from cell to cell through pits, (b) also functions in support (2) Vessel elements (a) wider, shorter thinner walled, are less tapered than trachids i) are aligned end to end, for easy flow of liquid ii) end of walls are perforated allowing free flow of water through long chains of vessel elements 4. Sieve-Tube Members: Food-Conducting Cells a. Chains of phloem cells that transport sucrose and other organic compounds b. are alive and functioning at maturity, an intact plasma membrane is required for function c. protoplasts lack a nucleus, ribosome and a distinct vacuole d. Angiosperm Sieve Tube members (1) ends have pores and are called sieve tube plates (2) pores facilitate movement of fluid between cells (3) have companion cells (a) support the cells that lack some organelles (b) help load sugar into these tubes B. The tree Tissue Systems of a plant 1. Dermal Tissue System (Epidermis)= single layer of tightly packed cells covering and protecting the young parts of the plant a. functions in protection b. in roots, root hairs are extensions of epidermal cells near root tips c. in leaves and stems produce a waxy cuticle that prevents water loss 2. Vascular Tissue system = xylem and phloem functions in transport, 3. Ground Tissue System = predominantly parenchyma, with some collenchyma and schlerenchyma. Fills upspace between dermal- vascular tissue, functions in photosynth, storage, and support 5. An overview of Plant growth A. Plants grow from the germination of the seed throughout their lifetime 1. Indeterminate growth = plants will grow as long as the plant lives a. most animals are determinate (stop growing after a certain size) b. certain plant organs such as flowers have determinate growth 2. Plants have finite lifespans a. Lifespan is genetically determined b. environmentally determined c. typical plant life cycles (1) Annuals - complete their life cycles in one year or growth season (2) Biennials - typically have life span of two years or growth seasons (3) Perennials - such as trees and some grasses may live many years B. Indeterminate growth is made possible by meristems (perpetually embryonic tissues) 1. Meristematic cells are unspecialized and provide growing cells 2. Dividing meristematic cells may remain in region (initials) or be displaced and placed into specialized tissues (derivatives) 3. Apical meristems- in root and bud tips allow plant to grow long (primary growth) 4. secondary growth or thickening of roots and shoots occurs in lateral meristems = cylinders of dividing cells extending along the lengths of roots and shoots 6. Primary growth ( apical meristems)(main body plan, long growth) A. Primary growth of Roots 1. growth is concentrate near tip and results in roots extending through the soil( protected by root cap) a. Zone of Cell Division (1) primary meristem (a) quiescent center- is meristematic reserve (b) three concentric cylinders( produce tissue of roots) i) protoderm (outermost layer, cuticle root hairs ii) procambium (develop phloem and xylem iii) ground meristem( filler, storage and regulates passage of material from outside the cell into the transport system b. Zone of Cell Elongation (1) cells elongate to 10 x original length (2) pushes root tip through soil (3)growth is sustained by the addition of new cells to the youngest end of the elongation zone. c. Zone of Maturation (1) Farthest form the root tip (2) new cells become specialized and complete their differentiation 2.Lateral roots (sprout form the outermost layer of the stele of a root) a. Pericycle, just inside endodermis may become meristematic and form lateral root b. forms a clump of cells and elongates and pushes through the cortex c. maintains its vascular connection to the stele of the main root. B. Primary Growth of Shoots 1. Shoot apical meristem is at the tip of the terminal bud a. differentiates into the 3 tissue systems b. flanks of the Apical meristem form the leaf primordia c. auxiliary buds form at the base of leaf primordia 2. shoot elongation occurs due to growth of older internodes below the shoot apex a. result of growth and division in the internode b. Intercalary meristems of grasses at the base of each internode allow elongation along the length of the shoot 3. Axillary buds may form branches later in the life of the plant a. differs from lateral roots b. originate at the surface of the shot and are connected to the vascular system which lies near the surface C.Primary Tissues of Stems 1. organized into strands of vascular bundles run the length of the stem a. converge at the transition zone (shoot->root) to join root stele 2. In dicots bundles are arranged in a ring with pith inside and cortex outside a. xylem faces the pith, phloem faces the cortex b. pith and cortex are connected by pith rays 3. In monocots vascular bundles are scattered throughout the ground tissue of the stem a. stem ground tissue is mostly parenchyma b. strengthened by collenchyma beneath the epidermis D. Tissue Organization of Leaves 1. cloaked by epidermis of tightly interlocked cells a. protects against physical damage and pathogens b. waxy cuticle prevents water loss c. stomata are pores flanked by guard cells which regulate gas exchange. d. Stomata allow transpiration (water loss by evaporation e. Stomata are more numerous on bottom side of the leaf 2. The ground tissue of the leaf is mesophyll a. mainly parenchyma cells equipped with chloroplasts b. Dicots have two distinct regions of mesophyll: (1) Palisade parenchyma = One or more layers of columnar cells of the upper half of a leaf (2) Spongy mesophyll = Irregularly shaped cells surrounded by air spaces through which oxygen and carbon dioxide circulate. Located in lower half of the leaf 3. leaf vascular tissue is continuous with stem through leaf traces a. continue in petiole as a vein, braces repeatedly throughout the mesophyll of leaf blade b. connects photosynthetic tissue with xylem and phloem c. skeleton for leaf support E. Modular shoot construction and phase changes during development 1. Shoots are constructed of a series of modules 2. each module consists of a stem, one or more leaves and an auxiliary bud associated with a leaf 3. elongation of internode gives plant its growth 7. secondary growth A. Basically produces another plant body. Resulting in growth in diameter B. results from growth from two lateral meristems: 1. Vascular cambium a. secondary xylem and phloem 2. cork cambium a. produces a covering that replaces the epidermis 3. Secondary growth is rare in monocots C. Secondary growth of stems 1.Vascular cambium meristematic parenchyma cells develop between the primary xylem and primary phloem of each vascular bundle and in rays of ground tissue between the bundles 2. fasicular cambium= cambium within the vascular bundle 3. Interfasicular cambium= Cambium in the rays between vascular bundles 4. TOGETHER FORM A CONTINUOUS CYLINDER DIVIDING CELLS AROUND THE XYLEM AND PITH OF THE STEM a. RAY INITIALS (MERSITEMATIC CELLS OF INTERFASCICULAR CAMBIUM) PERMIT LATERAL TRANSPORT AND STORAGE OF RESERVES b. Fusiform initials xylem on the inside of the vascular cambium and secondary phloem to the outside 5. Accumulated layers of secondary xylem produces wood. made mostly of tracheids, vessel elements and fiber a. deposited in annual rings b. secondary phloem becomes bark 6. Cork cambium cylinder of meristematic tissue forms protective layers of the secondary plant body a. as cork develops produces suberin in their cell walls and dye b. Bark is all tissues external to the vascular cambium (phloem, phelloderm, cork cambium and cork c. is a cylinder of fixed diameter. Will split as it goes D. Secondary growth of roots 1. Vascular cambium produces secondary xylem to its inside and secondary phloem to its outside 2. Cork cambium forms form the pericycle of the stele and produces the periderm, which becomes secondary dermal tissue a. periderm is impermeable to water, these roots function to anchor the plant and to transport water and solutes between the younger roots and the shoot system. b. will develop growth rings. Old roots and old stems tend to look similar. 1) Which of the following are true for Angiosperms A. Have flowers adapted for asexual reproduction and to survive in water B. Have two taxonomic divisions including Monocots and Dicots C. Use air as a source of carbon dioxide and sunlight D. Have roots adapted for anchorage, absorption of minerals and conduct water and nutrients E. The dicot form has only fibrous root system 1) Which of the following contain undifferentiated tissue, and are usually sites where plant growth will occur. a) Nodes b) internodes c) Axillary bud d) Terminal bud e) lateral meristem 2) The cells of a plant that are least specialized, tend to be thin and flexible, have a large central vacuole, and act in food storage a) Parenchyma cells, b) Collenchyma Cells c) Sclerenchyma Cells d) Tracheid cells e) phyllid cells 3) Both xylem and phloem move liquids, which of the following correctly compares the two: a) xylem is living and phloem is not b) phloem is living and xylem is not c) xylem uses the surface tension physical properties of water to move the water. d) Phloem uses surface tension to move water and sugar e) Phloem uses the plasma membrane to produce high and low concentrations that provide the energy to move the sugar containing water. 1) Which of the following statement is correct a) secondary roots are formed from auxiliary meristematic tissue (a bud) that grows perpendicular to the root. b) Branches form from the pericycle just inside the endodermis of the shoot. c) Soot apical meristem tissue may only develop into parenchyma tissue d) All stems grow from the bottom because of the present of Intercalary meristem e) In dicots the order of tissues is pith, xylem, phloem cortex, the pith and cortex are connected by pith rays. 1) B,C,D 2) C,D,E 3) A 4)b,c,e 5) E top Plant anatomy and Growth. Why study plants?? 1. They are our food 2. They have many medicinal properties 3. They are poisonous 4. They provide things for us. Morphology- study of the external structure Anatomy- study of the internal structure The Angiosperms! Kingdom Phylum Class Two major classes of angiosperms Monocot- one seed leaf Dicots- 2 seed leaves Link one two The major structures of a plant: root and shoot work together to form a whole. link Root provides water and minerals Shot provides CO2 and sunlight. Types of Plant Cells The following major types of cells make up the tissue and the structure of your plants. Parenchyma Cells  Are the least specialized - they can still divide and differentiate  Have only a thin primary cell wall, are thin and flexible  Protoplast has a large central vacuole  Function  Synthesize and store organic products  Photosynthesis in mesophyll cells  link Collenchyma cells  lack a secondary cell wall, primary wall is very thick and ridged  grouped in strands or cylinders, give support to young plants  living cells elongate as stems and leaves grow  link Sclerenchyma cells  function to support  thick secondary walls with lignin  once made they do not grow  2 major forms o fibers- long slender in bundles o schlerids- short and irregularly shaped  link These three types of cells make up the various tissues of a plant Dermal (epidermis, cork, bark)  a single layer that protects young plants  has root hairs  secretes waxy cuticle  in the adult may have various layers of thickness   link Vascular tissue  used for mass movement of liquid and solutes through the plant  link ground tissues (parenchyma)  is everything else that is not dermal or vascular  typically is just taking up space  link Plant Anatomy Stem  photos  labeled drawing simple, complex , more Root  photos  labeled drawing simple, complex Leaf  photos  labeled drawing simple , complex, more complex  leaf anatomical parts and description Indeterminate- plants grow as long as they live Plant life spans  annuals - Live 1 year (one season)  biennials - live for 2 years 1st year to grow 2nd to produce offspring  Perennials - live many years from a few seasons to thousands of years Meristems: are the perpetually embryonic tissue of the plant, allow for plant tissue culture. link The growth of the root (see fig 35.15)  Root apical meristem provides 3 structures on the plant side o Protoderm becomes epidermis o Ground meristem becomes cortex o Procambium becomes the stele  On the soil side the meristem becomes the root cap.  The root tip is pushed forward by the elongation of cells in the zone of elongation Primary growth in the stem is similar to the root. Secondary growth see figure 35.24 Plant Growth  Is due to the vascular cambium. Phloem is made on the outside and xylem is produced on the inside.  Periderm or cork cambium produces the cork. o This structure splits and gives bark its rough structure.