Effects on Particular Organs or Organ Systems

The discussion in this section concerns effects in organs or organ systems of vertebrate animals. Within that group the emphasis is, of course, on humans. As mentioned above, particular toxins will tend to target particular organs or organ systems. The liver and the kidney are common targets of toxic activity because of their role in detoxification and their large blood flow. The skin and eyes, lungs, and digestive tract are vulnerable to the more reactive toxicants, as they are the sites of...

Testing for Carcinogenicity and Teratogenicity

Carcinogenic potential can be detected by three types of tests long-term carcinogenicity studies, rapid screening tests, and biomarkers. Long-term tests are the most definitive. These generally use mice or rats and last the lifetime of the animals (18 and 24 months, respectively). Two or three dose levels are usually used, the highest being the maximum tolerated dose'' (MTD). The MTD is estimated from 90-day studies and is chosen so as not to produce severe noncarcinogenic toxicological effects...

Eukaryotic Cell Structure And Function

Membranes, penetrated by numerous protein pores. (In prokaryotes, the DNA is not isolated from the cytoplasm by a membrane, and the structure is called a nuclear region rather than a nucleus.) Each of the DNA molecules in the nucleus is contained in a chromosome. A chromosome is a complex of a DNA molecule and associated proteins. Chromosomal DNA forms a template for protein synthesis. Protein synthesis takes place outside the nucleus in the cytoplasm. The nucleus synthesizes RNA molecules,...

Chordates Including the Vertebrates

Finally, we come to the phylum that includes ourselves. The chordates incorporated evolutionary innovations that made it possible for them to grow to great size, forming the largest animals on land (dinosaurs and elephants) and in the water (whales). The four unique characteristics of the phylum Chordata are 1. They have the presence of a notocord at some point in their development. The notocord is a flexible skeletal rod that runs the length of the organism. It remains in adult lampreys and...

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ANot necessarily all strains can carry out the indicated reaction. aNot necessarily all strains can carry out the indicated reaction. Nitrifying bacteria are aerobic autotrophs that oxidize reduced nitrogen in two separate steps. Ammonium oxidizers such as Nitrosomonas, Nitrosospira, and Nitrosococcus convert ammonium to nitrite. (The first two are p-Proteobacteria, the third a g-Protoebac-teria.) Nitrite oxidizers convert nitrite to nitrate examples are Nitrobacter (a-Proteobac-teria) and...

Nervous System Organization

The nervous system may be the best example of the whole is more than the sum of its parts.'' Even accounting for the fact that the behavior of individual neurons is much more complex than described above, it is difficult to explain our higher behaviors, such as language, abstract reasoning, and self-consciousness, in terms of them. That is a far greater task than explaining the functioning of a computer in terms of the action of individual transistors. Those higher behaviors depend on neuronal...

Cloning and Recombinant DNA

A clone is a genetically identical copy of a DNA molecule, a cell, or an organism. Clones of DNA are produced in order to obtain sufficient genetic material for applications, such as DNA analysis or for producing recombinant DNA. Recombinant DNA is DNA formed by joining segments of DNA from different organisms. Recall that recombination occurs naturally between chromosomes in the same cell during meiosis and results in segments of DNA from one chromosome being included in another. Recombinant...

Water And Wastewater Disinfection Treatment

One of the most significant public health advances over the past century was that of developing, and then routinely applying, suitable engineering methods for disinfecting potable waters that could retard, and ideally obviate, the transmission of waterborne disease. Rudimental disinfection measures based on water filtration used by the ancient Egyptians and heat treatment have long been practiced, but the advent of commercially available chlorine during the late nineteenth and early twentieth...

Ebola

The index first noted case for the Ebola virus took place in Zaire in 1976, with more than 300 victims of this severe hemorrhagic bleeding fever. A second outbreak in Sudan killed another 150 people, and other, usually smaller outbreaks have since been reported, mainly in east, central, and southern areas of Africa. Ebola virus spreads through the body, with rapid necrosis death of cells in the infected organs, particularly those of the liver, lymph system, kidneys, ovaries, and testes....

Characterization of Prokaryotes

Before looking at the various groups of Bacteria and Archaea, it is useful to describe briefly some of the characteristics commonly used to differentiate among them. In many cases it is necessary first to isolate the organism and then to grow it in pure culture only one species present before testing. Shape Prokaryotic cells show a remarkable diversity of shapes Figure 10.2 showed a few . Most common are cylindrical rods Figure 10.8 , also called bacilli singular, Figure 10.8 Rod-shaped...

Arthropods

Arthropods jointed legs include the spiders, centipedes, millipedes, insects, and crustaceans. They represent an evolutionary advance that allowed them to form the greatest diversity and number of species of all the phyla, about 1 million species known. The advance was the development of a jointed exoskeleton made of chitin, a nitrogenous poly-saccharide, bound with protein. In crustaceans the exoskeleton also contains calcium salts for added strength. Other innovations with this phylum are...