Principles of Biology: Exploring the Animal Kingdom - Fall 2008, Study notes of Biology

Download Principles of Biology: Exploring the Animal Kingdom - Fall 2008 and more Study notes Biology in PDF only on Docsity! BIOL 101L: Principles of Biology Fall 2008 Invertebrates More than a million species of animals have been described. They occur in virtually every habitat, from the deepest recesses of the oceans to the driest deserts of the world. While these animals vary greatly in form and function, they all can be characterized as multicellular organisms that obtain their food by ingesting other organisms or their by-products (i.e., they are heterotrophic organisms). The fossil record indicates that the first animals arose in the Precambrian seas (> 600 mya), most likely from colonial protists that underwent a specialization of cells and a division of labor. Once established, this new way of life led to an explosive diversification of body forms. During the first 10-20 million years of the Cambrian period, representative of nearly every phylum of Kingdom Animalia emerged. The evolutionary history of animals has not been completely resolved, but a fairly comprehensive picture has emerged in recent years. Traditionally, biologists have generated hypotheses about evolutionary relationships by noting the phenotypic similarities and differences among species. More recently, comparisons of the DNA of both living and extinct species have been used to further clarify the relationships among animals. Currently, the animal kingdom is divided into several major groups, based on their evolutionary history (Fig. 1). Today, we will focus on the Invertebrata, a group that includes all animals that lack a vertebra (or back-bone). In Fig. 1, you can see that invertebrates belong to a paraphyletic group, which encompasses all animals except those with the Phylum Chordata. Invertebrates, both living and extinct, vastly outweigh chordates in terms of diversity and biomass; for example, The Invertebrata includes about 95% of the known species of animals. The phylogenetic tree depicts some of the evolutionary changes that define each group of animals. The sponges (Phylum Porifera) belong to a lineage that most closely resembles the first animals. These marine animals possess simple, asymmetrical bodies comprised of loosely aggregated cells. These animals lack true tissues and organs. A second evolutionary lineage includes the cnidarians (Phylum Cnidaria). Cnidarians are characterized by radial symmetry and the presence of true tissues that are organized into two layers (the diploblastic condition). Cnidarians also possess stinging cells called cnidocytes. The third major animal line contains most of the known phyla of animals. Members of this lineage possess three layers of tissue (i.e, they are triploblastic) and bilateral symmetry. Despite these two synapomorphies, this lineage contains a great diversity of body plans. Biologists further divide this lineage based on the presence of a body cavity (coelom) and the development of the digestive tract. Some of these animals have bodies with just one outer opening that serves as both a mouth and an anus. Others have two openings and the digestive tract forms a tube. Those animals with a mouth and an anus referred to as protostomes or deuterstomes, depending how the mouth and anus develop. In protostomes, the first embryonic opening, or blastopore develops into a mouth. In deuterostomes, the blastopore develops into the anus. In this and the following laboratory exercise, you will investigate body form and function in representatives of five major phyla: Porifera, Cindaria, Platyhelminthes, Annelida, and Arthropoda. The specific animals that you will study are the sponge, hydra, flatworm, earthworm, and crayfish. You will examine or dissect these organisms and relate their structures to their functions, lifestyles, and evolutionary history. Some structures will appear repeatedly among these organisms, while other structures will occur in only one or a few species. Thus, as you study each animal, keep in mind the relationship between form and function, the relationship between environment and lifestyle, and the evolutionary history of the organism. OBJECTIVES: • Compare and contrast the anatomy of representative animals, describing similarities and differences in organs and body form that allow the animal to carry out particular functions. • Relate the morphology of the animals to function in their environment. • Discuss how similarities and differences in morphology may indicate phylogenetic relationships. • Identify characteristics that are indicative of major phylogenetic branching points. • Know the bold structures listed for each organism as well as the Kingdom and Phylum. Use your Photographic Atlas for the Biology Lab (phot atlas) to identify structures. WHAT YOU WILL DO IN LAB: To guide your investigation of form, function, and relationships among five phyla. You will record your findings for each organism in the appropriate columns of Summary Table 1 near the back of this handout. This information will be used to answer questions in the Applying Your Knowledge section. Any information from these sections is fair game for next week’s quiz and the lab practical. If you want to read more material about each phylum, look at chapters 31 and 32 of your text, Life. 7.36). These carnivorous animals use tentacles arranged in a ring around the mouth to capture and ingest prey. The tentacles possess a unique feeding cell type called cnidocytes, which contain a stinging thread capsule called a nematocyst . When stimulated, the nematocyst turns inside out of the cnidocyte with explosive force, releasing a long thread that entangles prey. Most cnidarians are marine; however, a few live in freshwater. Included among the freshwater species is the microscopic, solitary organism, Hydra, the specimen you will examine today. Examination of Hydra: 1. Using a dissecting microscope, observe the Hydra’s structure and compare with Fig. 7.10- 11. Note the symmetry of the Hydra body plan. • Tap the edges of your Petri dish. Observe and compare the rate of elongation and the rate of contraction of this organism. • Find the mouth with its surrounding tentacles. Watch to see if a hydra catches any prey. In addition to their function in acquiring food, the tentacles are used in a type of locomotion that resembles a hand-spring. The hydra can attach its tentacles to the substrate and flip its body completely over, reattaching the base to a new position. 2. Study the prepared slides of hydra using the light microscope. Compare the sections with Fig. 7.12-14. Find the bud, basal disk, gastrodermis, and epidermis. Observe the tissue organization of the hydra body. Can you see two distinct tissue layers? What are these layers? Although you will not be able to see it, hydra do have a simple nervous system. The slow movements of Hydra are coordinated by a microscopic nerve net present in the body wall. Cnidarians lack a brain and nerve cord. 3. Think about how the body of the hydra is supported. How might the gastrovascular cavity provide support? Complete the characteristics of hydra in Table 1. Examination of sea anemone: Metridium senile is a common anemone in the northeastern United States and in northern Europe. It inhabits shallow, subtidal water and lives attached to rocks. 1. Find the tentacles, mouth, pharynx, gastrovacular cavity, and pedal disk (Fig. 7.36). Phylum Platyhelminthes—Flatworms, Flukes, and Tapeworms: Platyhelminths have bilaterally symmetrical bodies that are dorsoventrally flattened. These so-called “flatworms” have several evolutionary developments compared to cnidarians. Along with the evolution of bilateral symmetry came moderate cephalization and the ability for unidirectional movement. Flatworms also are triploblastic, a condition that has contributed to the development of true muscle and several other organs that are not present in the radiata. There are about 20,000 species of flatworms, grouped into three classes. Flatworms are free-living carnivores found under rocks, leaves, and debris in freshwater ponds and creeks. They move over these surfaces using a combination of muscles in their body wall and cilia on their ventral side. 1. Using a dissecting microscope, observe a live flatworm and compare to Fig 7.45-46.Note the mode of locomotion through the water. What does it do if you touch it with the tip of a probe? What does this indicate? Shine light from a pen light or flashlight onto the planarian, and describe its response. Find the head, eyespot, and gastrovacular cavity. Response to Touch: Response to Light: Examine a whole mount of Planaria using a light microscope and compare it with Fig 7.46. Examine the body for possible digestive tract openings. How many openings to the digestive tract can you see? The mouth is at the end of a muscular, protrusible pharynx that extends from the middle of the ventral side of the planarian. Find the pharynx and mouth. The proximal end of the pharynx opens into a branched gastrovascular cavity. The blunt end of the animal is the anterior or head region. Look for the pair of pigmented eyespots on the dorsal side of the head. These sensory organs are sensitive to light intensities and the direction of a light source, but cannot form images. Lateral to the eyespots are flaps called auricles that function for smell. Beneath the eyespots are two cerebral ganglia that serve as a simple brain. Two ventral nerve cords extend posteriorly from the ganglia, running the entire length of the body. The two cords are connected by transverse nerves to form a ladder-like nervous system. 2. Examine the prepared slide of a whole mount and cross-section of Planaria (Fig. 7.45). The evolution of three well-defined embryonic tissue layers has enabled flatworms to have a variety of tissues and organs, including reproductive organs and excretory organs. The mesodermally-derived excretory system consists of two lateral excretory canals and flame cells that move fluid through the canals. Respiratory, circulatory, and skeletal systems are lacking in the flatworm. How do you think the body of the worm is supported? How and where do you think gas exchange takes place? 3. Fill in the characteristics of the flatworm in Table 1. Examination of tapeworms (Taenia): Cestodes, or tapeworms, are highly specialized internal parasites and with few exceptions the adults inhabit the intestine of a vertebrate such as dogs. The tapeworm body consists of an anterior, head-like scolex and the trunk, or strobila, consisting of a linear series of segments, or proglottids. The scolex attaches the worm to the gut wall of the host. 1. Using Fig. 7.58-62, find the scolex, suckers, and proglottids. Where is the mouth? Phylum Annelida: Earthworms, Tubeworms, and Leeches: Annelids are a diverse group of animals that live in marine, freshwater, and moist terrestrial habitats. One group, the leeches, comprises blood-sucking parasites. Annelids range in size from microscopic to several meters in length. These animals share a number of features with nematodes (e.g, bilateral symmetry, three distinct tissue layers, a complete digestive tract), but have several new adaptations. EARTHWORM DISSECTION (pp. XXX-XXX of your photo atlas): 1. Examine the live earthworm (Lumbricus terrestris) and compare it with Fig 7.85. Earthworms burrow through rich organic soils. As you observe these animals, note features that are adaptations to the burrowing, terrestrial lifestyle. Identify the anterior end of the worm by locating the mouth. The mouth is overhung by a fleshy dorsal protuberance called the prostomium. The anus at the posterior end lacks his protuberance. A swollen glandular band, the clitellum, is located closer to the mouth than to the anus and also can be used to identify the anterior end. Note the segmented appearance of the earthworm. The posterior segments of the earthworm have four pairs of setae. Rub your fingers along the outer surface of the worm to feel the setae. What function might the setae have? Think of how the earthworm moves. 2. Your lab instructor will show you how to anesthetize you earthworm. Afterward, place your worm on a dissecting tray and pin the head and anus. Carefully cut open the body wall moving from the head to the anus. As you cut, pin back the body wall to expose the internal organs. Examine the dissected earthworm and compare to Fig. 7.86-91. Locate the digestive tract and its many specialized regions: the pharynx, esophagus, crop, gizzard, and intestine. Using the dissecting microscope, locate the longitudinal and circular muscle layers that line the body cavity. What advantage will these two muscle layers provide for locomotion? Look for the large blood vessel on the dorsal wall of the digestive tract. You may be able to see the five pairs of enlarged lateral blood vessels (hearts) around the anterior portion of the digestive tract. These lateral vessels connect the dorsal vessel to another large ventral vessel and also pump blood through the circulatory system. A pair of small, white coiled tubes called metanephridia are located in body cavity of each segment of the worm’s body. These organs remove wastes from the blood and from fluid within the body cavity. Look for the small brain just behind the prostomium on the surface of the digestive tract. Locate the two nerves that pass from the brain around the pharynx. These nerve tracts fuse ventrally and continue posteriorly as a ventral nerve cord with segmented ganglia. 3. Using a microscope, observe a prepared slide of a cross-section of an earthworm (Fig. 9.72). Locate the thin cuticle lying outside the epidermis. Speculate about its function in a terrestrial habitat. Locate the ventral nerve cord, usually lying embedded in muscle. 4. Fill in the characteristics of the earthworm in Table 1. APPLYING YOUR KNOWLEDGE 1. One of the major differences between cnidaria and the various worms examined in this exercise is radial versus bilateral symmetry. What is the advantage of radial symmetry for sessile (attached) animals and bilateral symmetry for mobile animals? What major evolutionary trend accompanies bilateral symmetry? 2. What is the adaptive significance of an animal having two separate openings to the digestive tract, as seen in annelids and arthropods? 3. What anatomical features are adaptations to a parasitic lifestyle? Which are adaptations to an aquatic lifestyle? To a terrestrial lifestyle? 4. A major new feature observed in the phylums Annelida and Arthropoda is a segmented body. Speculate about the advantages provided by segmentation. Table 1. Summary of 12 characteristics for comparative study of Kingdom Animalia Organism Symmetry Tissue Organization (No. of layers) Digestive Openings Circulatory System Habitat Locomotion Sponge Hydra Flatworm Earthworm Crayfish Organism Excretory System Respiratory System Support System Segmentation Nervous System Organization Appendages Sponge Hydra Flatworm Earthworm Crayfish