Abstract This paper examines how amphibians have not been exploited by humans like other animals have, they are kept as household pets and in some countries their flesh is seen as quite a delicacy. It therefore attempts to understand why are so many amphibian populations are in decline around the world. It shows how in some areas of the globe the decline is evidently due to loss of habitat but how in other areas, the reasons could be attributed to factors such as the depletion of the ozone layer or pollution. It looks at the advantages of amphibians to humans such as their use as environmental indicators and the use of their toxins as pain killers and covers methods of conservation.
From the Paper "Habitat loss seems to be a significant cause of the diminishing amphibian populations over much of the world. Human population growth has led to many of the wetlands that are essential for amphibians to be drained for agriculture, filled in or paved. In Britain alone, many years of draining wetlands in order to improve crop yields has resulted in the destruction of 82% of marshland. Now, only isolated patches remain. Deforestation is an added strain on amphibians as the dense canopy provides shelter and protection for not only the adult amphibians but also their developing young, from predators and ultraviolet light."
Abstract This paper provides an explanation of the evolutionary development of the circulatory, respiratory, digestive, sensory, and integumentary systems of phylum chordata. Comparisons between the systems various classes of phylum chordata are made, and the evolutionary advantages of the higher classes are highlighted. The paper is also accompanied with relevant diagrams and figures.
Outline:
Circulatory System
Evolution of the Heart
Piscine Heart
Amphibian and Reptilian Hearts
Avian and Mammalian Hearts
Respiratory System
Respiration in Agnatha and Chondrichthyes (Gills)
Respiration in Osteichthyes (Gills)
Respiration in Amphibians (Gills, Skin, Lungs)
Respiration in Reptiles, Birds, and Mammals (Lungs)
Digestive System
General Trends in Evolution of the Digestive System
Ruminant Stomach
Avian Gizzard
Sensory System
Usage of Olfactory System and Usage of Visual System
Prevertebrates: An Introduction
Anamniotes
Amniotes
Integumentary System
Anamniotes
Amniotes
From the Paper "One of the most fascinating developments made by the vertebrates was the heart. The complex and efficient four-chambered pumping mechanism possessed by mammals and birds evolved from what was only a muscular artery in protochordates. The heart itself is a specialized muscle responsible for circulating blood through the blood-vascular network. Marine protochordates possessed little more than a muscular region near the base of the aorta because, virtually anywhere on their bodies, they were capable of exchanging O2 and CO2 through their relatively thin skin. When scales and thicker skin emerged, however, this capability was lost, and respiration was localized in the pharyngeal region. An effective pumping device was required, and thus, the heart evolved."
Abstract This paper takes a look at the Permian and Cretaceous-Tertiary periods of life on Earth - pre-historic forms of life from sea creatures to land and air creatures. During both of these periods, mass extinction occurred and a comparison of these two extinctions is documented in this paper.
From the paper:
"From the perspective of daily human life, we often think of tragedy on the level of individual death and destruction, and the concept of mass extinction as being confined to a species or at worst, an ecosystem. However, over the course of the existence of the earth, the planet has weathered many greater catastrophes. Geologists must take a much longer-term perspective of catastrophe when studying extinction. This paper will compare and contrast the Permian and Cretaceous-Tertiary mass extinctions."
Abstract The following paper discusses the issue of genetic cloning by looking at its origins and scientific advances.The paper examines the research on genetic engineering and cloning that was used to clone plants, unicellular organisms, amphibians and simple mammals. It looks at significant advances in agriculture, industry and medicine. Although there are many potential benefits to this technology, the prospect of cloning humans has raised many practical, ethical and religious dilemmas that are discussed in this paper.
From the Paper "Genetic engineering is the changing of an organism's DNA, genetic material to eliminate unwanted traits or to produce desirable traits. The earliest form of genetic engineering dates back to the scientist Gregor Mendel who did experiments with peas. He bred only the peas with the most desirable traits in order to achieve a healthier and stronger pea (McCuen 8). This method, called selective breeding, is still used today with plants and animals in order to increase food production. Corn plants are selectively bred in order to produce a larger tastier kernel. Another type of genetic engineering called hybridization or crossbreeding involves breeding animals of different species in order to obtain the most desirable traits of both. Male donkeys are crossbred with female horses to produce mules, which are good work animals (Levine 1). Genes are made of DNA, deoxyribonucleic acid. The discovery of DNA in 1953 by Drs. Watson and Crick led to a much better understanding of the structure and function of genes. Since that scientific discovery many scientists have developed techniques to manipulate the DNA in genes in order to control different genetic processes. In the 1970s, scientists discovered restriction enzymes, which are enzymes that are able to cut and splice DNA. This led to the scientific technique known as recombinant DNA, which has paved the way for more sophisticated types of genetic engineering (McCuen 8)."
Abstract The paper begins by listing the frog's external characteristics and order of taxonomy. It continues to describe its physiology. It studies the behavior of the frog, dividing this topic up into behavior (including a look at its biological clock), learned behavior and social behavior. The paper includes a picture of the frog.
From the Paper "Rana boylii sierrae Camp. or foothill yellow-legged frog is found mostly in rivers and riverbanks, hiding around the rocks or emerges for sunlight. Ashton et al. writes that the species is morphologically identified in about 37.2 - 82.0 mm adult size, with dark and light gray dorsal color with some brown or red spots, much vague in the juvenile appearance. It is described that Rana boylii has ?rough skin, inconspicuous tympanum, horizontal pupils, fully webbed hind feet, poorly developed dorsal lateral folds, lack of dorsal stripe, and lack of black eye mask.?
Tags: external, characteristics, appearence, taxonomy, physiology, behavior, innate, learned, social
From the Paper "The Decline of the Amphibians
During the last 20 years, scientists worldwide have begun to notice some disturbing trends among amphibian populations. Moreover, the most troubling changes have occurred within the last decade. It seems that certain of the globe's 5,130 amphibian species have rapidly declined in number. Several species, in fact, may have already become extinct. To date, researchers do not know the reasons for this occurrence. However, some believe that atmospheric ozone depletion is responsible for the animals' decline. It could be that different amphibian species are highly vulnerable to ultraviolet radiation. Regardless of the underlying mechanisms though, the amphibians' plight may have serious implications. As "indicator" species, their decline could foretell major future environmental problems."
Abstract This paper will discuss the nature of the poison arrow frog, and seek to understand why it is now becoming endangered. By looking into the habitat of this amphibian, we can learn why this animal is in endangered from extinction.
Abstract This paper examines the group of arboreal anurans known as tree frogs, which possess the characteristic, expanded, terminal digital pads that assist in adhesion to the steep surfaces present in their natural environment. It looks at how the unique morphology and physical mechanisms of these structures have been studied for over a century and how it is only recently with the advances in transmission and scanning electron microscopy that it has become possible to study the pads in detail. It discusses how, even with this new insight into the ultrastructure of the pads, debate continues among zoologists over the nature and roles played by the various adhesive mechanisms of the toe pad and how the distribution of digital pads over five families suggests that the feature evolved independently many times in an interesting example of convergent evolution.
From the Paper "Wet or capillary adhesion was first proposed by Nachtigall as "a mechanism of direct adhesion through surface tension of a liquid intermediary fluid and whole pad suction" (1974), whereby toe pads adhere to a surface using the surface tension of the watery mucus exude. A modified version of this system was suggested by Hannah and Barnes in 1991 after conducting research on attachment and detachment mechanisms of the pads. The forces induced when toe pads were detached were measured with a force platform, and the results supported wet adhesion attachment, which was demonstrated through the existence of a concave meniscus at the interface between the pad and surface, showing connection via a fluid filled joint, and a velocity dependent resistance to shear forces of the pads, which is typical of systems using fluid as an adhesive."
Abstract This paper studies the Great Basin Spadefoot species and looks at where they can be found in the world. The writer discusses conditions and habitat for the Great Basin Spadefoot and describes their eating and living habits. The writer describes features of the species, including hibernation, reproduction, danger of extinction and various aspects of the spadefoot life. In this article, the writer discusses research and studies that have taken place regarding the Great Basin Spadefoot including mention of a large-scale collapse of an entire community of frog species and growth experiments. The writer makes use of the writings and studies of biologists and other experts to provide this insight into the spadefoot world.
From the Paper "Within the United States, the Great Basin Spadefoot lacks special state or federal status. They occur throughout the Columbia Basin and are locally common in many areas and within Washington state, there have been no declines documented. Spadefoots apparently can tolerate some habitat alteration, which often persists in irrigated agricultural lands. Moreover, it is believed that they may have actually increased in abundance due to the prevalence of breeding sites provided in some areas by irrigation water, however no systematic surveys have been conducted to document such patterns."
