Introductions Worksheet
  1. It has been suggested that lipid peroxides formed in the arterial wall are active in atherogenesis. The suggestion has been widely accepted as reasonable, since these compounds break down readily, initiating chain reactions as they do so and forming various products that are potentially toxic. Various experiments have been performed under a variety of conditions on both rats and humans to test the relative toxicity of these compounds.
  2. On September 19, 1985, an earthquake rattled the coast of Mexico in the state of Michoacan, about 400 kilometers west of Mexico City. Near the coast, the shaking of the ground was mild and caused little damage. As the seismic waves raced inland, the ground shook even less, and by the time the waves were 100 kilometers from Mexico City the shaking had nearly subsided. Nevertheless, the seismic waves induced severe shaking in the city, and some areas continued to shake for several minutes after the seismic waves had passed. Some 300 buildings collapsed and more than 20,000 people died. The Michoacan earthquake and others like it reveal a fundamental principle of seismology: seismic risk must be assessed from the ground up. In other words, the damage done by earthquakes depends not only on the seismic event itself, but also on the ground that underlies the buildings.
  3. The Canadian utility company Hydro-Quebec calls its massive James Bay hydroelectric project "La Grande Riviere: A Development in Accord with Its Environment." Is the project, in fact, "in accord"? It will dam twenty rivers, creating reservoirs with a total surface area exceeding that of Lake Ontario. According to Hydro-Quebec, all this damming can be accomplished without "unacceptable damage" to the wilderness. The company is mistaken. Any change in the natural flow of water in La Grande Riviere will disturb the delicate ecology at the river's mouth. In addition, the project will cause some tributaries to dry up, others to flood. Even now, dangerously high levels of mercury exist in reservoirs already created, threatening the health and livelihood of the local Cree Indians.
  4. Volcanic activity has long been suspected to cause significant short-term climate changes. Powerful volcanic eruptions typically inject huge quantities of gases and ash into the stratosphere where they produce optically significant aerosols that may remain for several years. Because of their small size, these aerosols are more effective at reflecting short-wave solar radiation that they are at attenuating the longer wavelength, Earth-emitted radiation. Thus, the aerosols alter the Earth's radiation balance by reflecting more of the sun's energy back to space and permitting the Earth to cool radiatively at about the same rate as before the eruption. The result is a net loss of energy for the Earth atmosphere system, or a cooling of the atmosphere and surface. Clouds generally produce a similar effect but for somewhat different reasons.

    5.  

     

  5. Why sexual reproduction evolved and how it is maintained in populations has been a pivotal question for evolutionists ever since Darwin. The capacity to reproduce sexually is nearly ubiquitous among species. Clearly it confers some advantage on the members of species that possess it. This advantage presumably consists of greater adaptability due to an increased rate of evolution. But how can a system evolve which is advantageous to the group and yet very costly to individuals as sex apparently is? This paper will elucidate some of the current thought on the costs and benefits of sexual reproduction.
  6. The enormous diversity of tropical trees is one of the great mysteries of biology. A plethora of possible explanations, some stressing bionic interactions, some not, have been suggested for this diversity. Each explanation seems to have evoked a plausible opposite (Leigh, 1990a). Resolving this confusion is essential. Our ignorance of what mechanisms preserve species diversity can render a reserve program utterly useless. Understanding what factors promote the coexistence of species is crucial for those seeking to maintain species diversity in small reserves.
  7. Since the mid-nineteenth century, when Darwin first proposed his seminal theory, evolution has ascended from a scientific hypothesis to virtual fact. Scientists and other educated persons have flocked around evolution in vigorous support of it, dismissing--sometimes in a most unscientific manner—criticism and contradictory evidence. Yet despite this concerted effort to defend evolution and its special, almost untouchable, status within the scientific community, some scholars have begun to seriously question the viability of evolution as a scientific theory. The problems with evolution are becoming increasingly difficult to ignore, and although alone each does not necessarily refute the theory, together these difficulties form a serious challenge to evolution. This paper examines two major areas in which evolution runs into trouble: the fossil record and natural selection.
  8. Many authors have been engaged in the study of the identification and detection of specific biologically active molecules by autographic methods. These procedures involve suspending nutritionally deficient mutant bacteria with specific nutrient requirements in an agar medium. After incubation with the required nutrilite, they show zones of growth. This technique offers many advantages over other methods of conducting bioassays. It is simpler, less subject to inhibitors, and it can be used with very small samples. The main disadvantage, namely that very concentrated samples are required, has been overcome in one laboratory by incorporating tetrazolium salts in the agar.