Answer to Question 1
In investigating a suspected chemical, a toxicologist would conduct animal tests, investigate human involvement with the chemical, and present the information linking the dose (the level of exposure multiplied by the length of time of which exposure occurs) with the response (some acute or chronic effect or the development of tumors). Toxicologists may also use cell cultures to study mutagenicity, carcinogenicity, or endocrine activity. Data from epidemiological studies will also be utilized if available. The overall goal is to link the quantity of exposure to the degree of response to a specified outcome. The outcome can be a measure of morbidity (nausea, edema, headache, tremor) or mortality (immediate or delayed).
Answer to Question 2
Salinization is the accumulation of salts in and on the soil to the point where plant growth is suppressed. Salinization occurs because even the freshest irrigation water contains at least 200 to 500 ppm (0.02 to 0.05) of dissolved salts. Adding water to dryland soils also dissolves the high concentrations of soluble minerals that are often present in those soils. As the applied water leaves by evaporation or transpiration, the salts remain behind and gradually accumulate as a precipitate. Because it happens in drylands, salinization is considered a form of desertification, since it renders the land less productive or even useless. Salt is a limiting factor for plants: when salt levels are too high the plants die, leaving the land bare and vulnerable to erosion.
Mechanisms that convey positional information during embryonic development.
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