This Document Contains Chapters 28 to 30 CHAPTER 28: VERTEBRATES WHERE DOES IT ALL FIT IN? Chapter 28 provides more detail about the diversity of animals highlighted in Chapter 27. It goes into more detail about modern animals. Students should be encouraged to recall the principles of animal classification covered in Chapter 27. The information in chapter 28 does not stand alone. Students should know that vertebrates are interrelated and originated from a common ancestor of all animals. SYNOPSIS The phylum Chordata includes the animals with which we are most familiar and most closely related. Their principal features are: a single, hollow, dorsal nerve cord; a flexible, dorsal notochord; pharyngeal slits; and a postanal tail. All chordates have these four characteristics at some time in their development. The most primitive nonvertebrate chordates (subphylum Urochordata) include tunicates and lancelets. Larval tunicates resemble primitive tadpoles and clearly possess all chordate characteristics. Adult tunicates are sessile, colonial organisms that secrete a cellulose tunic around themselves. They seemingly lack many of the expected characteristics. The lancelets are scaleless, fishlike marine organisms. They are filter feeders and create water currents via cilia on the anterior end of the gut. The subphylum Vertebrata is well-represented by marine, freshwater, and terrestrial organisms. They possess a vertebral column, distinct and well-differentiated head, neural crest cells that participate in the development of vertebrate structures, internal organs, and an endoskeleton made up of cartilage and bone. Their circulatory and excretory systems are markedly different from all other animals. Vertebrates are divided into nine classes; five contain the aquatic fishes and four are terrestrial tetrapods. Key characteristics of fishes include a vertebral column, jaws and paired appendages, gills, single-loop blood circulation and nutritional deficiencies. The class Cephalaspidomorphi is made up the jawless fishes, the lampreys, parasitic and nonparasitic types, and all breed in fresh water while the class Myxini contain the hagfishes, jawless fishes with no paired appendages, scavengers, mostly blind but having a well-developed sense of smell. Under the traditional classification scheme, both were labeled jawless fish and lumped into the superclass Agnatha. Both retain the notochord as adults and possess cartilaginous skeletons. Larval lampreys superficially resemble the lancelets, although they are more efficient feeders and create water currents via a muscular pharynx. Class Chondrichthyes included the sharks, skates, and rays. These are streamlined hunters, possess cartilaginous skeletons, have no swim bladders and undergo internal fertilization. They are jawed fishes. The horizontal fins of the sharks and rays improve their swimming ability, forcing the buoyant animals downward in the water as they swim forward. Their skin is covered by small denticles from which teeth are derived. Class Sarcopterygii include the lobe-finned fishes, a group of bony fishes that are ancestral to amphibians possessing paired lobed fins. Class Actinopterygil consist of the ray-finned fishes, which are the most diverse group of vertebrates. These fish possess a denser, less buoyant skeleton and have evolved a gas-filled swim bladder to help position themselves in the water. Their scales are composed of thin, bony plates and they possess a well-developed lateral line sensory system. Bony fish possess several unique characteristics including gills, a gill cover, and a single-loop circulation. Terrestrial vertebrates include the classes Amphibia (frogs and salamanders), Reptilia (lizards and snakes), Aves (birds), and Mammalia (mammals). They evolved from the lobe-finned fishes. As the first land-dwelling vertebrates, amphibians needed certain characteristics to ensure their survival. Among these are: legs and strong thoracic skeletons for support and locomotion, efficient air-breathing structures (lungs) as gills collapse out of water, a redesigned heart and circulatory system to deliver more oxygen to the walking muscles, water-bound reproduction to keep their eggs from desiccation and a means to keep their own bodies from drying out. The three orders of amphibians are Anura consist of frogs and toads, amphibians without tails; Urodela consist of salamanders and newts that have elongated bodies, long tails and smooth, moist skin; and, Apoda that includes the caecilians which are a group of tropical, legless, burrowing amphibians that resemble worms but have jaws with teeth. All are greatly dependent on maintaining a moist skin for respiration except for the dry-skinned toads. Reptiles are less dependent upon water having amniotic eggs in which the embryo is encased in a shell; dry, watertight skin made up of scales; and, pulmonary breathing by expanding and contracting the rib cage. Their legs are better positioned for mobility and speed, and their heart and circulatory systems are more efficient. Four major forms of reptiles took turns dominating the land. In order they are the pelycosaurs, the therapsids, the thecodonts, and the dinosaurs. Today’s reptile orders include Chelonia (turtles and tortoises), Squamata (snakes and lizards), Rhynchocephalia (tuataras), and Crocodilia (alligators and crocodiles). Fishes, amphibians, and reptiles are ectothermic animals; they regulate their body temperature by taking in heat from the environment. Birds and mammals are endothermic; they maintain their temperature by the expenditure of internal energy. There are 28 orders of bird, 166 families. The most ancient birds are the flightless birds such as the ostriches. Next are the waterfowl such as ducks and geese. Next are the woodpeckers, parrots, swifts, and owls. The songbirds, the largest order of birds, the Passeriformes evolved next. The more specialized orders such as shorebirds, birds of prey, flamingos, and penguins appeared later. Birds are clearly evolved from reptilian ancestors. Two primary characteristics distinguish birds from reptiles: feathers and flight skeleton. Their feathers are modified reptile scales. Feathers are obviously important for flight, but also insulate as birds are endotherms. They need to maintain a high body temperature so that metabolism in their flight muscles can proceed at a faster rate. Bird bones are thin and hollow to reduce weight. Many are fused to provide rigidity for flight. Birds are the only vertebrates that have a fused collarbone (wishbone) and a keeled breastbone. Birds have extremely efficient respiratory and circulatory systems to provide sufficient oxygen to sustain flight. Mammals evolved from therapsids reptiles over 220 million years ago. They were a minor group as long as the dinosaurs flourished. With their extinction, mammals rapidly diversified. There are about 4500 living species of mammals. The key characteristics of mammals are milk ¬producing glands and hair. Mammal hairs are not derived from reptile scales or bird feathers, though they serve a similar protective, insulating function. Other characteristics include endothermy, placenta (in some mammal species), and heterodont dentition (different forms of teeth), digestion of plants, hooves and horns, flight (different from birds). Monotremes are egg-laying mammals that retain many primitive, reptilian characteristics. The duck-billed platypus and two species of spiny anteater are the only living monotremes. Marsupials are the pouched mammals found almost exclusively in Australia. A major difference between marsupials and other mammals is their pattern of embryonic development – completing its development outside of the mother’s body in a pouch. Placental mammals produce a true placenta that nourishes their embryos through the course of development. Gestation is totally internal for an extended period of time. Both marsupials and placental mammals give birth to live young and nourish them with milk. Although not the most numerous vertebrates, because of their size, mammals are certainly among the most obvious. There are 19 orders of mammals, 17 are placental mammals. Primates are an order of mammals and have two distinct features: grasping fingers and toes and binocular vision. Primates further split into two groups: prosimians (before monkeys) and the anthropoids (monkeys, apes and humans). The hominoids include the apes such as the gibbon, orangutan, gorilla, and chimpanzee. Apes have larger brains than monkeys and lack tails. Hominids include humans and their direct ancestors. Hominids walked upright, their vertebral column is more curved, human spinal cord exists from the bottom of the skull, the pelvis has become broader, the big toe is no longer sideways, and the lower limbs are longer than the upper limbs. A hominid evolutionary tree is made up of six species of Australopithecus (A. anamenis, A. boisei, A. aethiopicus, A. africanus, A. robustus, and A. afarensis) and, seven Homo species (H. rudolfensis, H. habilis, H. ergaster, H. erectus, H. neanderthalensis, H. heidelbergensis and H. sapiens). LEARNING OUTCOMES 28.1 Nonvertebrate Chordates Do Not Form Bone 1. Describe the nonvertebrate chordates. 2. Distinguish between lancelets and tunicates. 28.2 Almost All Chordates Are Vertebrates 1. Distinguish vertebrates from other chordates. 28.3 Fishes Are the Earliest and Most Diverse Vertebrates 1. Describe the evolutionary innovations of fishes. 2. Describe the evolution of jaws in early fishes. 3. Explain how a lateral line system works. 4. Explain the importance of a swim bladder. 28.4 Amphibians Were the First Terrestrial Vertebrates 1. Describe the distinguishing characteristics of amphibians. 2. Contrast the three major orders of living amphibians. 28.5 Reptiles Fully Adapt to Terrestrial Living 1. Describe the significance of the evolution of the amniotic egg. 2. Distinguish between synapsids and diapsids. 3. Describe the characteristics of the major groups of living reptiles. 28.6 Birds Are Essentially Flying Reptiles 1. Describe the key characteristics of birds. 2. Explain why some consider birds to be one type of reptile. 3. Explain the adaptations birds have to cope with the energetic demands of flight. 28.7 Mammals Are the Least Diverse of Vertebrates 1. Describe the characteristics of mammals. 2. Compare the three groups of living mammals. 28.8 Primates Are the Mammals That Gave Rise to Humans 1. Distinguish among the major groups of primates. 2. Describe the role of bipedalism in the evolution of early hominids. 3. Contrast Australopithicenes and the genus Homo. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 28 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students are unsure of the evolutionary relationships between different vertebrate groups • Students think that all vertebrate groups evolved at about the same time • Students believe that all animals are mobile • Students believe that most animals are vertebrates • Students are unfamiliar with interrelations of the different organ systems • Students believe that all animals have identical organ system structures • Students believe that animals exclusively reproduce sexually • Students believe that the fins of modern fish evolved into limbs • Students do not equate wings to tetrapod front limbs • Students are unaware of molecular methods of animal classification • Students are resistant to the anthropoid lineage of humans • Students believe that vertebrate evolution is flawed because of the absense of “missing links” INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Discuss flight and the anatomy of wings in birds and mammals. Discuss endothermy versus ectothermy relative to insects, birds, and mammals. Discuss the developmental structure of the cardiovascular system in various classes of vertebrates. Discuss the differences between monotremes, marsupials, and placental birth/hatching. Discuss the theory of birds and mammals from reptiles with respect to the development of feathers and fur. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 28. Application • Ask students to explain why amphibians are more diverse in warmer climates. Analysis • Have students explain why some land living amphibians lack lungs while not known mammal has no lungs. • Have students explain the benefits and risks of flight in vertebrates. • Ask students to explain why terrestrial mammals do not achieve the tremendous size of aquatic mammals. Synthesis • Ask students to explain the discovery that reptiles are capable of producing a placenta. • Have students hypothesize why sharks are the top ocean predator instead of a bony fish. • Ask students to find a medical application that exploits the knowledge gained by research on limb formation in amphibians. Evaluation • Ask students to evaluate the claim that vertebrate evolution is restricted in diversity compared to arthropods. • Ask students to evaluate the consequences of people replacing meat and poultry with fish as a staple diet. • Ask students to evaluate the accuracy of using amphibians as an indicator of environmental disturbances. VISUAL RESOURCES Compare the larval stages of tunicates, lancelets, and lampreys. Obtain the jaw of a small shark and compare the teeth to scales found on shark skin to tactilely illustrate the denticles. Bring in skulls and skeletons for all vertebrate animals to show similarities in bone types but differences in structure. Show that differences in structure are related to differences in use as dictated by their environment and/or habitat. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Virtual Vertebrate. Introduction This demonstration permits the class to see a virtual frog dissection to supplement a discussion on vertebrate morphology and organ systems. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Virtual Frog Dissection at http://froggy.lbl.gov/cgi-bin/dissect Procedure & Inquiry 1. Explain to the class that you will be demonstrating the vertebrate characteristics using a virtual frog 2. Load up the website and click on the White Diamond icon to flip the frog around while describing various vertebrate characteristics 3. Then “check” the various buttons underneath the frog to add or remove organ systems. 4. Have the students explain the characteristics of the organ systems. 5. Ask the students briefly explain how the environment and lifestyle affect the morphology of the various organ systems in the different vertebrates. LABORATORY IDEAS A. Comparative Vertebrate Anatomy This activity asks students to investigate the similarities and variation in vertebrate body plans. a. Review the generalized characteristics of chordates to the class. b. Tell students that they will be forming research teams to investigate the similarities and differences of the vertebrate body plan compared to a purported vertebrate ancestor. c. Provide students with the following materials to be distributed into research teams who dissect one animal: a. Preserved perch b. Preserved lizard or salamander c. Preserved rat d. Preserved pigeon e. Dissecting materials f. Rulers d. First have the students design a “model” ancestral vertebrate body plan that can be drawn as a reference for comparison on the board. e. Instruct students to investigate and describe the body and organ system characteristics of their specimen. f. Then tell the students to explain the similarities and differences of their vertebrate to the hypothetical vertebrate ancestor model. g. Have students share their findings and explain the reasons for differences in the body plans. They should be encouraged to discuss the role of hox genes and embryological development in determining the adult body form. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students do a lesson do a program the importance of vertebrate biodiversity for a civic group. 2. Have students tutor high school students animal diversity. 3. Have students volunteer on environmental restoration projects with a local conservation group. 4. Have students volunteer at the educational center of a zoo or marine park. CHAPTER 29: PLANT FORM WHERE DOES IT ALL FIT IN? Chapter 29 builds upon the general information on plant diversity provided in Chapter 26. A quick summary of Chapter 26 is essential for success at covering Chapter 29. In addition, students should be encouraged to recall the principles of eukaryotic cell structure, photosynthesis, and evolution associated with the particular features of plant cells. SYNOPSIS • • Vascular plants have roots and shoots. The root system penetrates the soil and absorbs water and minerals. Roots also anchor the plant. The shoot consists of stems and leaves. The stem supports the leaves, which are the primary photosynthetic structures in plants. Flowers and other reproductive structures are also supported by the stem. Plants are composed of three types of tissues: dermal tissue, ground tissue, and vascular tissue. • • Plant meristems are undifferentiated cells that can divide indefinitely and give rise to many types of cells in the plant. Cell division in apical meristems results in elongation of the root and shoot. They give rise to three types of embryonic tissue: protoderm that becomes epidermis, procambium that becomes primary vascular tissue, and ground meristem that becomes ground tissue parenchyma cells. Division in lateral meristems produces an increase in girth of shrubs and most trees. Woody plants have two cylinders of lateral meristems: cork cambium produces the cork cells of the outer bark, and vascular cambium cells give rise to secondary vascular tissue. Cork cambium also replaces the epidermis, and produces the bark on stems and roots in plants that experience secondary growth. The basic plan of a plant includes root and shoot, the latter being composed of stems, leaves, flowers, and fruit. Although the development of the basic plant form and structure is rigidly controlled, some aspects of leaf, stem, and root development are flexible. Plants undergo continuous development that is greatly affected by external events. Plants must be highly responsive to their environment as they cannot generally pick up their roots and grow somewhere else. The three basic plant tissue types include dermal tissue (epidermis), ground tissue (parenchyma cells), and vascular tissue (xylem and phloem). • • Primary growth helps to establish the basic body-plan of plants, whereas secondary growth allows plants to increase in diameter. Secondary growth appears to have evolved independently in several groups of vascular plants, allowing the development of tree-like organisms with thick trunks. Early vascular plants lacked stems, leaves, and roots. These organs became useful with inhabitation of the land. The vascular tissues formed by the primary meristems functioned in conduction just as in modern plants. Sieve tube members conduct carbohydrates away from areas where they are manufactured or stored, typically roots and leaves, while vessel members and tracheids conduct water and minerals upward. These tissues are associated together in primary tissues. In secondary growth, phloem is located on the periphery, and xylem tissue develops more centrally in the stem. Conduction is continuous between root and shoot tissues. • Epidermal cells derived from dermal tissue cover all parts of the primary plant body. It may contain specialized cells. Guard cells are paired, chloroplast-containing cells located on either side of the stoma. They accommodate the passage of oxygen and carbon dioxide as well as the diffusion of water that results from transpiration. Trichomes are hair-like outgrowths that help regulate heat and water balance and can vary greatly in form. Root hairs are extensions of single cells on the outer surface of growing roots. They greatly increase a root’s surface area and are the entry points for water absorption. • • Plant ground tissue exhibits several characteristic kinds of cells including parenchyma, collenchyma, and sclerenchyma. Only parenchyma and collenchyma are capable of further cell division. Sclerenchyma fibers and sclereids are lignified, structural elements that possess tough, secondary walls. Xylem conducts water upward from the roots and is composed of tracheids, dead cells that taper at the ends and overlap one another, and vessel members, dead, hollow, cylindrical cells arranged end-to-end. Water is conducted in a continuous stream throughout the plant body, passing through pits in tracheid cell walls, eventually diffusing into the atmosphere in transpiration. Vessel members, found primarily in angiosperms, conduct water and dissolved minerals more efficiently than do tracheids. Primary xylem is derived from procambium, and secondary xylem forms from the vascular cambium. Xylem also consists of parenchyma cells that are produced by special ray initials of the vascular cambium, and they function in lateral conduction and food storage, and fibers that are major components of modern paper. Phloem, the principal food-conduction tissue in vascular plants, is composed of sieve cells or sieve-tube members. Seedless vascular plants and gymnosperms have only sieve cells while most angiosperms have only sieve tube members that are more advanced and efficient than sieve cells. They function with living companion cells that have plasmodesmata connecting the cytoplasm of associated sieve tube members. • Roots have a simpler anatomy than do stems, and they do not produce projections analogous to leaves or flowers. Developing roots have four distinctive regions: root cap, zone of cell division, zone of elongation, and zone of maturation. Primary growth in the root occurs at the root tip. Daughter cells on the root tip side become root cap cells, whereas the others pass through the other zones, whose boundaries are not clear, before they complete differentiating. Root caps are unique to plant roots, and are composed of inner columella cells and outer, lateral root cap cells, which are continuously replenished by apical meristems. Root cap cells produce a mucilaginous material that eases root tips through the soil, and provides a medium for growth of beneficial nitrogen-fixing bacteria in some plants. Root caps respond to gravity, due to amyloplasts in columella cells although the exact nature of the gravitational response is not known. Mitosis in the zone of cell division occurs toward the edges of the inverted dome-shaped apical meristems. Daughter cells then divide into the three primary tissues: protoderm, procambium, and ground meristems. Activity in the zone of elongation causes lengthening of roots as new cells finally elongate. No further increase in cell size occurs above the zone of elongation, and the mature parts of the root remain stationary throughout the plant’s life. Cell differentiation takes place in the zone of maturation. Epidermal cells with very thin cuticles form on the root surface; many develop into root hairs. Parenchyma cells, produced by the ground meristems immediately interior of the epidermis, form the cortex whose inner boundary cells differentiate into the endodermis. Its primary walls contain suberin, produced in bands called Casparian strips. This waxy layer determines what minerals and nutrients enter the root xylem. The pericycle lies just inside the endodermis and is the perpetual source of lateral roots, and part of the vascular cambium in eudicots. Tissues interior to the endodermis constitute the stele. Primary xylem cells differentiate in the center of eudicot roots forming vascular bundles around parenchyma cells called pith. Primary phloem cells also differentiate near the xylem. Secondary xylem subsequently forms toward the inside of the root vascular cambium, and secondary phloem forms to the outside. Cork cambium forms the bark; however, cork cambium is not present in either monocots or herbaceous eudicot species. There are two primary root morphologies: tap roots or fibrous root systems. Both function in anchorage and absorption. Adventitious roots arise primarily along young stems of some plant species. They include aerial roots, pneumatophores, contractile roots, parasitic roots, food and water storage roots, and buttress roots, and they carry out an interesting variety of functions. • • Stems form from initiatives in shoot apical meristems. Primordia tissues, located intermittently along stems, develop into other shoots, leaves, or flowers. The arrangement of leaves may optimize their exposure to the sun. Leaves are attached to stems at nodes, separated by regions called internodes. Leaf buds are terminal if attached to the tip of a twig, and axillary if formed along the length of it. Axillary buds form lateral branches. Woody stems may live for many years, and they develop distinctive markings that reflect prior events, such as bud scale scars the form when protective winter bud scales drop. Such markings are useful in wintertime identification of plants. Internally, apical meristems produce primary meristems that contribute to the length of stems and form the three primary meristems: protoderm, ground meristems, and procambium. In stems that exhibit primary growth, ground tissue divides into centrally located pith and an outer cortex. Also, vascular tissue is embedded in the ground tissue as scattered bundles in monocots, and as a cylindrical outer ring in eudicots. Vascular cambium produces xylem and phloem in the same manner as in roots. Cork is renewed constantly when the cork cambium produces cork to the outside and phelloderm cells to the inside. Cork inhibits water and gas exchange with the stem tissues except in unsuberized patches called lenticels. Bulbs, corms, rhizomes, runners and stolons, tubers, tendrils, and cladophylls are examples of stem modifications, and major modes of vegetative reproduction for some plants. They have all the features of stems: leaves at nodes, buds in leaf axils, and internodes. Commercial and private industry often uses segments of modified stems for species propagation. • • Leaves are the primary photosynthetic organs of plants, and consequently, they are vital to life on earth. Initiated as uncommitted primordial by apical meristems, they are extensions of shoot apical meristems and stem development. Microphylls are small, early evolutionary forms of leaves primarily associated with the order Lycophyta. Megaphylls, characterized by numerous veins, are found on most plants. Flattened blades and slender petioles of most leaves demonstrate a shift from radial symmetry to dorsal-ventral symmetry. Stipules may be present. The veins are vascular tissues that run through the leaf in parallel patterns in monocots, and in netted patterns in eudicots. Leaf blades exhibit various morphologies, classified as simple or compound. They are arranged in alternately, as opposite pairs, or in whorls. Leaf surfaces consist of epidermal cells that lack chloroplasts and are covered by a waxy cuticle, and may have various glands and trichomes, but generally lack stomata. These are typically located on the lower epidermis. Mesophyll tissues, interspersed with veins of various sizes, occupy the interior of leaves. In eudicots, it is composed of tightly packed, chloroplast-laden palisade cells, and loosely arranged, spongy parenchyma cells. Spongy mesophyll is interspersed with intercellular spaces that connect to the stomata, permitting gas exchange with the environment. Differentiation of mesophyll does not occur in monocots. Modified leaves evolved in different environments, and include bracts, spines, reproductive leaves, window leaves, shade leaves, and insectivorous leaves. • • LEARNING OUTCOMES • 29.1 Vascular Systems in Stems Connect Plant Roots with Leaves 1. Distinguish between the functions of roots and shoots. 2. Describe the three types of tissues in a vascular plant. 3. Compare primary and secondary growth. 29.2 Plants Contain Three Principal Tissues 1. Explain how dermal tissue provides adaptations for terrestrial lifestyle. 2. Compare and contrast the different kinds of ground tissue. 3. Distinguish between xylem and phloem. 29.3 Roots Have Four Growth Zones 1. Describe the four regions of a typical root. 2. Describe functions of modified root. 29.4 Stems Provide Support for Aboveground Organs 1. List the potential products of an axillary bud. 2. List three functions of modified stems. 29.5 Leaves Are a Plant’s Photosynthetic Organs 1. Distinguish between a simple and a compound leaf. 2. Compare the mesophyll of a monocot leaf with that of a eudicot leaf. 3. Describe the functions of modified leaves COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 29 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that plants lack tissues and organs. • Students are unaware of all of the functions of roots. • Students are unaware of all of the functions of stems. • Students believe that only leaves can carry out photosynthesis. • Students believe that the reproductive structure of all plants are flowers. INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE • This chapter epitomizes the complexity of plant form, resulting from plant growth. It is imperative that teachers think through and plan on how to present the information in exciting and understandable ways. Perhaps an explanation of cells to tissues to organs will be helpful. Or, consider initiating a discussion about the essential features needed for plant function: roots to anchor, stems to support, leaves for photosynthesis, tissues for conduction and storage and protection, etc. Have students understand the make-up of typical monocot and eudicot stems and roots, then “work backward” and examine the embryonic origins and subsequent differentiation of the respective cells and tissues. Once students understand the basic tissue types, they can work more expertly with this fascinating information. Hands-on sketching, however, interpretable to anyone except the artist, is a compelling way to encourage mastery, and it can be fun. • HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 29. Application • Have students describe how damage to apical meristems would affect plant growth. • Have students explain the evidence of organ structure in plants. • Ask students to explain how a plant lacking leaves and roots would be able to carry out photosynthesis. Analysis • Have students explain the advantages and disadvantages of an herbaceous stem over a woody stem. • Have students explain why a particular leaf has much fewer leaf hairs on its lower surface than on the upper surface. • Ask students to explain the benefits and risks up upright stem growth in plants. Synthesis • Ask students to explain the possible applications of the discovery of a mutation that increases the growth rate of vascular tissue formation. • Have students hypothesize why the agricultural value of a genetic engineering technique that can modify the role of ground tissue in a plant. • Ask the students to explain why trees in trees in construction areas exhibit a die-off of branches even if they are not damaged by people or machinery. Evaluation • Ask students evaluate any possible risks of using genetic engineering to increase the growth rate of root crops such as carrots. • Ask students to evaluate the consequences of people over-using herbicides that kill weeds by inhibiting meristem growth. • Ask students to evaluate the accuracy of using herbaceous eudicots as a model for all plants. VISUAL RESOURCES • Three-dimensional models are very helpful, although they are generally better suited to small lectures or laboratory use. In large classes, overheads of 3-D drawings are most appropriate. Take time to explain the plant parts and processes so that students do not experience “information overload” regarding these valuable organisms in which many are not interested. • • Secondary growth is difficult for beginning students. They especially don’t understand that when a cell divides one of the daughter cells moves inward and the other outward. One could illustrate this on an overhead using “cells” cut from colored pieces of acetate, with color differentiation being associated with cell type and cell position. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Cyber Plant. Introduction This demonstration shows students how computer modeling is used to study plant structure, growth, predation, and reproduction. Software developed by the University of Calgary, Canada provides an excellent example of plant modeling. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Virtual Plant Animations at http://www.biologie.uni-hamburg.de/b-online/virtualplants/ipimovies.html Procedure & Inquiry 1. Explain to the class that you will be demonstrating a new way botanists are studying plant structure and development 2. Load up the website and show students the different models available for investigation 3. Click on one of the animations and ask the students what they are observing. 4. Then ask the students to explain how the researchers obtained the data to produce the animations and models. 5. Ask the students to briefly explain the value of using the models that they observed. LABORATORY IDEAS A. Cell Wall Architecture This activity asks students to investigate the architecture of plant cell wall using a novel technique that highlights the cell wall. a. Review the generalized characteristics of plant cells and cell walls. b. Tell students that they will be using a special laboratory procedure for isolating cell walls from the rest of the cell structures. c. Instruct that you want them to look at differences in cell specialization and cell wall morphology in various plant specimens. d. Provide students with the following materials to be distributed into research teams who dissect one animal: a. Various fresh fruits and vegetables from grocery store b. Microscope c. Microscope slides d. Petri plates e. Forceps f. Sharp scalpel g. Distilled water in squeeze bottle h. Reagents i. 0.5% Nonidet P40 ii. Bleach diluted fivefold iii. 10 mM NiCl2 iv. 1% Na2S e. Instruct the students that will have to follow the steps below to successfully view the intricacies of cell wall structure in the materials they are comparing. a. Slice paper thin sections of the specimens i. In the Petri plate wash the plant sections in 0.5% Nonidet P40 for 15 minutes. ii. Drain Petri plate and wash plant section in bleach for 15 minutes. iii. Drain Petri plate and wash plant section in 0.5% Nonidet P40 for 15 minutes. iv. Drain Petri plate, rinse with distilled and wash plant section in 10 mM NiCl2 for 5 minutes. v. Drain Petri plate, rinse with distilled water and soak plant section in 1% Na2S. A dark color will form on the cell walls. vi. Specimens should be rinsed and viewed under the microscope. f. Instruct students to investigate and describe cell diversity and cell wall morphologies of the specimens. g. They should record the differences and hypothesize about the reasons for any similarities and differences. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students do a lesson do a program on plant structure to elementary students. 2. Have students tutor high school students learning plant structure. 3. Have students volunteer on environmental restoration projects with a local conservation group. 4. Have students volunteer at botanical garden or nature center. CHAPTER 30: PLANT REPRODUCTION WHERE DOES IT ALL FIT IN? Chapter 30 builds upon the general information on seed plants provided in Chapter 29. A quick summary of Chapter 29 is essential for success at covering Chapter 30. In addition, students should be encouraged to recall the principles of eukaryotic cell structure and evolution associated with the particular features of plants. SYNOPSIS • Flowering plants have been tremendously successful, evolutionarily, because they produce flowers and true fruit. Their success is an excellent example, perhaps the best-known example, of co-evolution among plants and animals. The consequence of co-evolution is greater genetic diversity due to a wider distribution of plant gametes. In stable environments, however, there may be less need for genetic diversity, and there, asexual reproduction (cloning) may be advantageous. • • Flowers form in response to highly regulated processes including light, temperature, and internal and external signals, a process analogous to reproductive development in animals. In angiosperms, internal development changes are called competence, that is, competence to respond. Competence is followed by phase change, the transition to morphological changes. These changes may be quite obvious or very subtle. Phase change requires both sufficient signal and the ability to perceive the signal. The signals determine which flower parts—sepals, petals, stamens, and carpels—form, and where they form. Environmental cues are important. Genetic manipulations are possible. • • There are three known genetically regulated pathways to flowering. One, the light-dependent pathway influences how plants respond to seasonal changes in the relative length of day and night. Plants are classified as short-day, long day, or day-neutral, accordingly. This classification correlates with the amount of uninterrupted darkness that induces flowering. This also is known as photoperiodism, or photoperiodic response. Short-day plants flower when daylight becomes shorter than a critical length. Long day plants flower when daylight becomes longer than a critical length. Day-neutral plants flower when mature regardless of day length. Several different forms of phytochrome and a blue-light sensitive molecule called cryptochrome perceive photoperiod. A conformational change in cryptochrome triggers a cascade of events that leads to the production of a flower. The temperature-dependent pathway supports the theory that cold temperatures can either accelerate or permit flowering in many species. Similarly to the effects of light, the outcomes of this pathway ensure that flowering occurs at optimal times for different species. Vernalization refers to the phenomenon whereby some plant species require a chilling period in order to flower. Vernalization may function with autonomous pathways in the promotion of flowering. The autonomous pathway may have evolved first. It functions independently of external cues except for basic nutrition. Day-neutral plants depend on this pathway as they appear to “count and remember” until, at some point, shoots, perhaps in conjunction with inhibitory signals from roots, are determined to flower. The three flowering pathways lead to an adult meristem becoming a floral meristem by either activating or repressing the inhibition of floral meristem-identity genes that turn on floral organ identity genes. All this activity only leads to the beginning of flower formation. Flowers contain the haploid generations that will produce gametes. Flowers also allow for an increase in pollination opportunities, likely allowing for an increase in genetic diversity. A great variety of floral phenotypes exist, explaining the great variety of angiosperm species. Two major evolutionary trends lead to this diversity: (1) Separate floral parts became grouped together, and (2) Floral parts were reduced or lost. Other evolutionary trends affect flower symmetry. Radial symmetry is believed to be more primitive than bilateral symmetry. Mutations in either flowers or pollinators may prevent fertilization from occurring. • • Fertilization is the union of gametes, that is, eggs and sperm, from either the same or different flowers of the same species. In angiosperms, the gametophyte generations are very small. The female gametophyte is the embryo sac. The male gametophytes are pollen grains whose shapes are specialized for specific flower species. A complex series of events called double fertilization occurs uniquely in the angiosperms. In this process, one sperm cell fertilizes the egg while a second one helps from the endosperm that nourishes the embryo. • • Pollination refers to the transfer of pollen that forms within pollen sacs from microspore mother cells to the stigmas of female flowers. This process may or may not lead to fertilization. • Pollination in early plants occurred passively, by such mechanisms as the wind, a random event. Subsequently, co-evolution of flowers and animals, especially insects (bees, moths, butterflies, birds, bats, and other animals) has enhanced diversity and success of both. Wind is still an important agent for pollination. Wind-pollinated plants are not dependant on live pollinators. • • While cross-fertilization or out-crossing contributes to genetic diversity, self-pollination is ecologically important, as pollinators are not required. Diversity is still present meiosis, and recombination still occurs in the development of both male and female gametophytes. Outcrossing is facilitated when stamens and pistils are separated. Monoecious plant species possess both male and female flowers while dioecious species have either male flowers or female flowers but not both. In monoecious species, male and female flowers may mature at different times, further enhancing opportunities for outcrossing. Such plants are referred to as dichogamous. • • Least genetic variability results from asexual reproduction in which only mitotic cell division occurs. One form, vegetative reproduction, provides for progeny cloned from parents. Examples of vegetative reproduction are runners, rhizomes, suckers, and adventitious plantlets. Apomixis is another form that occurs in some plants, for example, some citruses, grasses, and dandelions. In apomixes embryos are produced asexually from parent plants. Asexual reproduction tends to occur in marginal or harsh environments, and the progeny are genetically identical to the parent individual. Tissue culture, a technique that allows for regeneration of whole plants from individuals cells or tissues, is an artificial type of asexual reproduction. • • Flowers are characterized as complete and incomplete, depending on the number of whorls of parts: calyx (outermost whorl consisting of sepals), corolla (interior to calyx, consisting of petals), androecium (collective term for the stamens, the male structures), and gynoecium (collective term for the female parts: single or fused carpel/s or pistil/s that include stigma, style, and ovary) Ovules, contained in ovaries, develop into seeds. The embryo is contained within the seed coat along with the endosperm. • The basic body plan of a plant is established while it is still an embryo. Only a portion of it is formed when it first emerges from the soil, and differentiation and development continue throughout its life cycle. Shape and form come about through regulation of the amount and pattern of cell division. The first division results in two different cells types. Early on, cells can give rise to various cell and organ types, but as development proceeds, cells with multiple potentials are restricted to meristematic regions. Apical meristems are involved in growth and differentiation of root and shoot tips during embryogenesis, and help establish the three basic tissues: dermal, ground, and vascular. Concurrently, food supplies for the embryo are formed differently, in angiosperms and gymnosperms, and differentiation of ovule tissue forms protective coverings around the embryos, indicating the end of embryogenesis. Germination will occur when appropriate environmental and hormonal signals contribute to the breaking of seed dormancy, which can last for many years. The first embryonic cell division is asymmetric, producing one small cell that is destined to become the embryo while the other becomes the suspensor that connects the embryo to the food supply in the seed. Cells near the suspensor form the root while those at the other end form the shoot. Tissues differentiate when the embryo is in the globular stage, but shoot and root apical meristems are controlled independently. The outermost cell layer, the protoderm, becomes protective dermal tissue. The ground tissue forms the bulk of the embryo interior and functions in food and water storage. Procambium forms at the core of the embryo and forms the future vascular tissue. Knowledge of plant development has been advanced greatly with the examination of the small, mustard-related Arabidopsis thaliana. This plant has a short generation time and is able to produce thousands of offspring in only two months. Many gene mutations affecting pattern formation are known, helping elucidate the mechanisms of early plant development. A heart-shaped embryo forms from divisions in the globular stage. Embryonic cells, not meristematic cells, give rise to cotyledons (seed leaves), initiating morphogenesis during which rates and planes of cell division bring about the 3-D form of a plant body. Microtubules and actin, as well as hormones and other factors are involved. Food reserves especially starch, lipids, and proteins are produced during embryogenesis. In fact, these proteins are so abundant that molecular biologists used them during early gene-cloning research. Food reserves in seeds reflect the evolutionary trend toward enhancement of embryo survival. • Embryo development ceases, generally, following the differentiation of meristems and cotyledons, and resumes when environmental conditions are favorable for plant growth. Various adaptations provide for timely germination of different species. When environmental conditions signal germination, the seed absorbs water, enzymes and hormones including gibberellic acid become activated, and metabolism including protein synthesis in the embryo resumes. Environmental signals may involve certain intensities and wavelengths of light, and temperatures, sometimes for long periods of time. Using its food reserves, the seed resumes growth orienting itself so the root grows downward and the shoot grows upward. Grains possess a single cotyledon that forms a scutellum that conveys nutrients from the endosperm to the embryo. The emergence of root and shoot is quite variable. In peas and corn, the cotyledons remain underground. In beans, radishes, and onions, they emerge above ground and become photosynthetic. Most young seedlings are very susceptible to stress, especially pathogens and drought, during this period. • Plants live for variable periods of time. There is not a direct correlation between life span and mode of reproduction. Nonetheless, woody species that incur secondary growth tend to live longer than herbaceous species that do not form secondary growth. Herbaceous species, however, may be classified as annuals since they grow, flower, and set seed prior to dying during one growing period. Biennial species require two seasons during which to accomplish this, and perennial species continue to grow, indefinitely. Perennial plants include woodland, wetland and prairie species as well as woody species such as shrubs and trees. The latter are considered deciduous if their leaves abscise and fall each year, appearing bare during stressful times such as winter in most temperature areas. Evergreens, on the other hand, drop their leaves throughout the year, and never appear bare of foliage. Abscission is the process whereby senescent plant parts, as leaves, respond to hormonal changes and environmental cues, promoting death and drop of those parts. Fall season color displays of many deciduous species in temperature zones involve the abscission process. • LEARNING OUTCOMES 30.1 Angiosperm Reproduction Starts with Flowering 1. Describe the general life cycle of a flowering plant. 2. List the parts of a typical angiosperm flower. 3. Differentiate between microgametophytes and megagametophytes. 30.2 Flowers Exist to Attract Pollinators 1. Contrast the various ways pollen may reach a flower. 2. Compare the effectiveness of different animal pollinators. 3. Contrast animal and wind pollination. 4. Explain how self-pollination may be favored. 5. Describe three evolutionary strategies that promote outcrossing. 6. Describe the process of double fertilization. 30.3 Embryo Development Begins as Soon as the Egg Is Fertilized 1. Discuss the role of the suspensor in embryo development. 2. Describe how three tissue systems arise in the embryo. 30.4 Seeds Protect Angiosperm Embryos 1. Describe how food reserves develop in the embryo. 2. Explain how seeds help to ensure the survival of a plant’s offspring. 3. Discuss the role of environmental conditions in seed germination in some plants. 30.5 Fruits Ensure Widespread Seed Dispersal 1. Identify the structures that develop into fruit. 30.6 Germination Begins Seedling Growth 1. Describe how seed germination occurs. 2. Contrast the pattern of shoot emergence in bean (dicot) with that in maize (monocot). 30.7 Plant Life Spans Vary Widely 1. Distinguish between herbaceous and woody perennials. 30.8 Asexual Reproduction Is Common Among Flowering Plants 1. Define apomixis. 2. List examples of plant parts involved in vegetative reproduction. 3. Outline the steps involved in protoplast regeneration. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 30 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students are unaware that plants develop environmental adaptations. • Students believe that plants lack tissues and organs. • Students are unaware of all of the functions of leaves. • Students do not equate pollination with sexual reproduction • Students think pollen are one and the same as sperm • Students are unaware that plants produce eggs • Students are unaware that plants undergo embryological development • Students are unaware of the relationship of flowers to other plant parts. • Students are unfamiliar with the chemistry of plant defensive chemicals. • Students believe that all flowers are insect pollinated. • Students do not believe that plants produce eggs. • Students believe that all plants produce seeds. • Students are confused by the role of gametophytes and sporophytes. • Students are not sure of the role of meiosis in plant life cycles. INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE • Hints regarding flower terminology: staminate flowers have stamens, pistillate flowers have pistils. Monoecious means “one house”; therefore a monoecious plant has both staminate and pistillate flowers on a single plant. Dioecious means “two houses,” thus a dioecious plant has two different kinds of plants (male and female), each with its own type of flower. • • Pollination refers only to the transfer of pollen. This event may or may not be followed by fertilization. What factor/s can impede fertilization? • HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 30. Application • Have students describe petals are important in determining the pollination strategy of a plant. • Ask students to explain how flowering can be affected by chemicals that inhibit gibberellins. • Ask students to explain why temperature is a factor in flower induction in certain plants. Analysis • Have students describe how mutations to flower arrangement genes could affect a plant’s reproductive success. • Have students explain how pesticide use can affect the plant composition of an area. • Have students compare the relative effectiveness of insect versus wind pollination. Synthesis • Ask students design an experiment to test if UV light is a factor in insect pollination of flowers. • Have students design an experiment to test if self-pollination is increased under stable environmental conditions. • Ask the students develop an experiment to determine the role of stamen number in wind pollinated plants. Evaluation • Ask students evaluate the benefits and consequences of breeding self-pollinating fruit crops. • Ask students to evaluate the reasons for propagating agricultural plants by cloning instead of using self-fertilization. • Ask students to evaluate the effectiveness of improving flower and fruit production in agricultural plants by increasing fertilizer levels in the soil. VISUAL RESOURCES • Three-dimensional models or drawings of flowers are extremely helpful, especially in presenting the idea of whorls and flower specializations, and double fertilization. The best models are those that can be taken apart to show the interior of the pistil and anther. Of course, living specimens are ideal. • Also examine various types of fruit from the outside inward, and then let your students eat the fruit! Scanning electron micrographs of pollen are very impressive in showing some of the beautiful, unseen intricacies of nature. Those pollens that cause common allergies are very spiky while other pollen grains are globular. • Show examples of long-day, short-day, and day-neutral plants. This helps students realize that photoperiodism is not a remote concept. Discuss the methods used to initiate flowering at certain seasons. Easter lilies do not bloom in early March without being forced by altering light and temperature. Certain succulents are similarly forced and produce blooms at Easter, Thanksgiving, or Christmas. Many temperate plants will not bloom when grown in southern climates, including lilacs, forsythia, and gladiolus. These all require exposure too cold for a certain period. However, farther north than the Appalachians, gladiolus freezes if left in the ground over winter. Most varieties of apples do not flower or fruit when grown beyond certain latitudes. • IN-CLASS CONCEPTUAL DEMONSTRATIONS A. UV Vision Introduction This demonstration shows students flowers differ in appearance under visible light and ultraviolet light. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Ultraviolet Flowers website at http://www.naturfotograf.com/UV_flowers_list.html Procedure & Inquiry 1. Explain to the students that you want show flowers under two lighting conditions. 2. Tell the students to pay close attention to the flowers images. 3. Load up the website and click on various flowers. 4. First show the flower under visible light. 5. Then scroll down to the flower under UV light. 6. Ask the students to describe the differences between flowers under visible and UV light. 7. Also ask them to explain any variation in how flowers appear under UV light. 8. Then ask them to explain if there is a reason that the flowers appear differently under UV light. B. Name the Pollination Strategy Introduction This demonstration asks students to guess the pollinator and the pollination strategy by looking at images of flowers. Materials • Computer with Media Player and Internet access • LCD hooked up to computer • Web browser linked to Angiosperm Pollination Syndromes website at http://www.cas.vanderbilt.edu/bioimages/pages/pollination.htm • Printout of Angiosperm Pollination Syndromes website as a reference for the answers to the queries • Images from Angiosperm Pollination Syndromes website cut and pasted onto a work document so that each flower takes up one whole page when projected on a screen Procedure & Inquiry 9. Explain to the students that you want to guess the pollinator and pollination strategy of each plant. 10. Show a flower and ask a student in the class to make a guess and justify their answer. 11. Acknowledge the answer and provide the correct answer if the student was incorrect. 12. Continue until you feel the students understand how to recognize form and function in flowers. LABORATORY IDEAS A. Floral Morphology This activity encourages students to identify variations in floral morphology. a. Explain to students that they investigating the morphology of flower variation. b. Then explain that they will be using brine shrimp amoebocytes as a model system for looking at the effectiveness of cell-killing power. c. Tell students that they will be investigating the conditions needed for fungal spore germination in two types of fungi. d. Provide students with the following materials a. Dissection microscope b. Sharp scalpel c. Probes d. Flowers: i. Carnation ii. Lily iii. Gladiolus iv. Aster v. Delphinium vi. Orchid e. Computer with Internet access and the following links: i. http://www.ndsu.edu/instruct/mcclean/plsc731/flower/flower3.htm ii. http://www.cc.ndsu.nodak.edu/instruct/mcclean/plsc731/flower/flower2.htm iii. http://www-biology.ucsd.edu/labs/yanofsky/flower/intro_to_flower_dev.htm iv. http://biology.clc.uc.edu/fankhauser/Wildflowers/Plant_categories/Plant_Families.htm f. Book with flower parts diagram e. Instruct students to observe the differ flowers and record their observations about: a. Number and arrangement of petals b. Number and arrangement of sepals c. Number of whorls d. Makeup of whorls e. Number and arrangement of stamens f. Organization of the carpels g. Fusion of floral parts. f. Have the students use the information from the provided websites to hypothesis about the mutations that produced the genetic variety of the flowers they observed. g. Then tell the students to share their hypotheses with the class. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students tutor high school students learning plant reproduction. 2. Have students volunteer with a garden club on a community garden project. 3. Have students give a demonstration on the diversity of flowers elementary students. 4. Have students volunteer at botanical garden or nature center. Instructor Manual for Understanding Biology Kenneth Mason, George Johnson, Jonathan Losos, Susan Singer 9780073532295, 9781259592416
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