LESSON-2 (1).pdf

ZOOLOGY: THE SCIENCE OF ANIMALS  At the end of this chapter, the students should be able to; define and give examples of, herbivore, carnivore, omnivore, insectivore, saprophyte, detrivore and parasitic animal; give a representative animal, enumerate its adaptive characteristics;...

ZOOLOGY: THE SCIENCE OF ANIMALS  At the end of this chapter, the students should be able to; define and give examples of, herbivore, carnivore, omnivore, insectivore, saprophyte, detrivore and parasitic animal; give a representative animal, enumerate its adaptive characteristics; present to the class the concept of division of labor inside an animal cell; and  group representative organisms as to their inherited body plan that can be described in terms of symmetry, body cavities, partitioning of body fluids, body segmentation and cephalization.  Modern animals are considered as the most adaptable organisms when it comes to displaying the effects of various evolutionary processes. Some of the general characteristics of animas are as follow: 1. Cellular Level: Animals do not have tough cell wall and plastid but they have smaller vacuoles and centrioles. 2. Animals have a great variety of specialized tissues, organs and systems. 3. Animals are heterotrophic organisms – herbivore, carnivore, omnivore, insectivore – saprophyte, detritus feeder or decomposer (gets nourishment from dead organisms or decaying organic material) – and parasitic. 4. Animal movement is mostly due to muscular contraction coordinated by nerves. Animals are generally active. 5. Most animals have skeletal system which supports and protects the body organs. 6. Animals have sense organs that aid in locating prey and to escape from predators. 7. Animals can reproduce sexually or asexually. Some give birth alive and some are hatch from eggs.  The metazoan or multicellular animals, have cells differentiated into tissues and organs that are specialized for specific functions. The metazoan cell is only a specialized part of the whole organism and is incapable of independent existence. There are four levels of organization. Each level is more complex than the one before. 1. Cellular Level of Organization Cellular organization is an aggregate (collection) of cells that are functionally differentiated.  A division of labor is evident, so that some cells are concerned with, for example, reproduction and others with nutrition. Protoplasmic Structures 1. NUCLEUS a. Nuclear membrane b. Nucleoplasm c. Nuclear pore d. Nucleolus e. Genetic materials Protoplasmic Structures 2. CYTOPLASM a. Endoplasmic (Rough & Smooth) b. Golgi body/apparatus c. Lysosome d. Vacuole e. Mitochondrion Protoplasmic Structures 2. CYTOPLASM f. Ribosome (Free and attached) g. Cytoskeleton h. Centriole Protoplasmic Structures 3. CELL MEMBRANE a. Phospholipid bilayer b. Structural proteins b.1 Peripheral protein b.2 Integral protein or transmembrane protein 2. Tissue Level of Organization A step beyond the preceding is the aggregate of similar cells into definite pattern or layers, thus becoming a tissue.  An excellent example of a tissue in cnidarians is the nerve net, in which the nerve cells and their process form a definite tissue structure, with the function of coordination. 3. Organ Level of Organization The aggregation of tissues into organs is a further step in advancement. Organs are usually made up of more than one kind of tissue and have a more specialized function than tissue. Ex. Eyespots, proboscis and reproductive organs of flatworm are well- defined organs. 4. Organ System Level of Organization When organs work together to perform some function, it is the highest level of organization – the organ system. Typical of all the higher forms, this level of organization such as complete Digestive System and Circulatory System, is first seen in nemertean worms.  Animals become more complex. They tend to become larger. Caused by the increasing complexity as a result of specialization and division of labor within body tissues. Large body size offers advantages. A. It is obvious in the predator-prey contest. Predators are almost always larger than their prey. Exceptions are few and usually are related to an aggressive behavior that compensates for small size. B. Larger animals can move about at much less energy cost than small animals. C. Large size improved homeostasis. It accompanies greater internal stability that is the capacity to regulate the internal environment of the body. The ability to maintain internal stability despite changes in the environment allows organisms to invade hostile habitats.  The body of a multicellular animal consists of three elements – cells, body fluids, and extracellular structural elements.  The functionally specialized cells of metazoan develop into various tissues made up of similar cells performing common function. The basic tissue types are nervous, connective, epithelial, and muscular. These tissues are organized into larger functional units called organs and organs are associated to form systems.  The body fluids of animals permeate all tissues and spaces in the body. They are naturally separated into fluid compartments. The two major fluid compartments are the intracellular space, that is within the cells and the extracellular space, outside the cell. Intracellular space (within the cells) ▪ -70% water, smaller molecules, ions, and proteins - where the organelles are suspended Extracellular space (outside the cells) ▪ - fluid part of the blood outside the blood cells, 90% water, 10% ions, proteins, dissolved gases, nutrient molecules, and wastes. Extracellular space (outside the cells) ▪ - tissue fluid occupies the spaces surrounding the cells, found between the vessels and the cells, composed of sugar, hormones, O2, CO2, water, fatty acids, salt.  Sugar O2 Fatty acids CO2 Salt Hormones Water  The third element of the metazoan body is the extracellular structural elements. This is supportive material of the organism such as connective tissue, cartilage, and bone. It provides mechanical stability, protection, and a depot of materials for exchange and serves as a medium for extracellular reactions. Extracellular structural elements (supportive material of the organism) ▪ – for protection, responsible for maintaining a framework and support for organs and the body as a whole, connection and binding (ex. ligament, tendon), can store fat, calcium, phosphorus, transport substances, and repair tissue damage. Extracellular structural elements (supportive material of the organism) ▪ – reduce friction, provide support in bony areas where flexibility is needed. Extracellular structural elements (supportive material of the organism) ▪ - give shape and support for the body, protection of internal organs, storage for minerals, and formation and storage of new blood cells.  Every organism has an inherited body plan. Four of the most important determinants of multicellular body plans are symmetry, presence or absence of body cavity, presence or absence of segmentation and cephalization. ANIMAL SYMMETRY Symmetry refers to balanced proportions or the correspondence in size and shape of parts on opposite sided of a median plane. Planes and Directional Terms (front end) (back end)  (top end) (bottom end) ANIMAL SYMMETRY Asymmetrical animals are those with no pattern or symmetry ANIMAL SYMMETRY Bilateral symmetry only a sagittal plane can divide the animal into two mirrored portions – right and left halves. ANIMAL SYMMETRY Bilateral animals make up all of the higher phyla and are collectively called the Bilateria. They are better fitted for forward directional movement than radially symmetrical animals. ANIMAL SYMMETRY Radial symmetry is the symmetry around a central axis. (more than two planes produce mirror halves) ANIMAL SYMMETRY A variant form is biradial symmetry in which, only two planes passing through the central axis produce mirrored halves.  Radial and biradial animals are primarily sessile, freely floating, or weakly swimming. The two phyla that are primarily radial, Cnidaria and Ctenophora, are called the Radiata.  Animal Symmetry Radial Symmetry Bilateral Asymmetry Biradial Symmetry Symmetry sponge Radiata Bilateria cnidarian flatworm ctenophoran nematode echinoderm annelid arthropod molluscs chordate BODY CAVITIES In higher forms of animal, the main body cavity is the coelom, a fluid-filled space that surrounds the gut which usually forms during the early stage of animal development. It provides the following: (1) increased body flexibility (2) increased space for visceral organs and; (3) permits increase in size and complexity. (4) The coelom allows for compartmentalization of the body parts, so that different organ systems can evolve and nutrient transport is possible.  The coelom provides coelomic animals with a “tube-within-a-tube” arrangement. The true coelom develops within or inside the mesoderm and is thus lined with mesodermal epithelium or mesoderm germ layer called the peritoneum. 1. Acoelomate Bilateria 1. Acoelomate Bilateria The more primitive bilateral animals do not have true coelom. In fact, the flatworms and a few others have no body cavity surrounding the gut. The region between the ectodermal epidermis and the endodermal digestive tract is completely filled with mesoderm in the form of parenchyma. 1. Acoelomate Bilateria 2. Pseudocoelomate Bilateria 2. Pseudocoelomate Bilateria Nematodes and several other phyla have a cavity surrounding the gut, but it is not completely lined with mesodermal peritoneum. This type of body cavity is called a pseudocoel and its possessors also have a “tube-within-a-tube” arrangement. 2. Pseudocoelomate Bilateria A pseudocoelomate is an organism with body cavity that is not derived from the mesoderm. A true coelom is lined with a peritoneum which serves to separate the fluid from the body cavity. In a pseudocoelomate, the body fluids bathes the organs, and receive their nutrients and oxygen from the fluid in the cavity. 3. Eucoelomate / Coelomate Bilateria 3. Eucoelomate / Coelomate Bilateria The bilateral animal possesses a true coelom that in lined with mesodermal peritoneum.  Body Cavity Acoelomate Pseudocoelomate Eucoelomate Bilateria Bilateria Bilateria flatworm nematode annelid arthropod molluscs echinoderm chordate METAMERISM (SEGMENTATION) Metamerism is the serial repetition of similar body segments along the longitudinal axis of the animal body. Each segment is called metamere or somite.  In earthworm and other annelids, metamerism is most clearly represented. The segmental arrangement includes both external and internal structures of several systems. There is repetition of muscles, blood vessels, nerves and the setae of locomotion. True metamerism is found in three phyla: Annelida, Arthropoda, and Chordata.  Superficial segmentation of the ectoderm and the body wall may be found among many diverse groups of animals.  In segmented body plan of a shrimp, each segment has at least one pair of appendages. Appendages can be legs, antennae, flippers, claws, etc. Some somites can be fused together as the cephalothorax of the shrimp. While other are not fuse like the abdomen of the shrimp. CEPHALIZATION The differentiation of a head end is called cephalization and found chiefly in bilaterally symmetrical animals. The concentration of nervous tissue and sense organs in the head bestows obvious advantages to an animal moving through is environment head first.  This is the most efficient positioning of instruments for sensing the environment and responding to it. Usually, the mouth of the animals is located on the head as well, since so much of an animal’s activity is concerned with procuring food.  Cephalization is always accompanied by differentiation along an antero-posterior axis, polarity. In simple animals, polarity differentiates the oral end from the aboral end.